[v6] drm/mcde: Some fixes to handling video mode

Message ID 20191217150959.17215-1-linus.walleij@linaro.org
State Accepted
Commit c8d4a56082eebabbf96ddb86238808c30124f06b
Headers show
Series
  • [v6] drm/mcde: Some fixes to handling video mode
Related show

Commit Message

Linus Walleij Dec. 17, 2019, 3:09 p.m.
The video DSI mode had not really been tested. These fixes makes
it more likely to work on real hardware:
- Put the active width (x width) in the right bits and the VSA
  (vertical sync active) in the right bits (those were swapped).
- Calculate the packet sizes in bytes as in the vendor driver,
  rather than in bits. Test the calculations agains a
  spreadsheet and confirmed by debug prints to be reasonable.
- Also verified the register values with relative confidence
  to register dumps from the Samsung GT-I8190 boot loader
  graphics. We are not identical but not off by far either.
- Error out if the current mode and refresh frequency doesn't
  work out. (In the future we may simply want to scale down
  the vrefresh.)
- Handle negative result in front/back/sync packages and fall
  back to zero like in the vendor driver.
- Put in lots of clarifying comments and references to the
  documentation where the code is hard to understand.
- Set the DSI_VID_VCA_SETTING2 field
  DSI_VID_VCA_SETTING2_MAX_LINE_LIMIT to blkline_pck - 6 as in
  the vendor driver and mask the field properly.
- Set the DSI_VID_VCA_SETTING1 field
  DSI_VID_VCA_SETTING1_MAX_BURST_LIMIT to blkeol_pck - 6 to
  blkeol_duration - 6 as in the vendor driver.

Cc: Stephan Gerhold <stephan@gerhold.net>
Fixes: 5fc537bfd000 ("drm/mcde: Add new driver for ST-Ericsson MCDE")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

---
ChangeLog v5->v6:
- DSI_VID_VCA_SETTING1_MAX_BURST_LIMIT should be blkeol_pck - 6
  not blkeol_duration - 6.
- Parenthesize some calculations.
ChangeLog v4->v5:
- Restore log order, last verstion of the changelog inadvertedly
  merged v3 and v4 into v3 since I thought I didn't send out v3...
- Parens in blkeol_pck = bpl - (mode->htotal * cpp) - 6 for
  explicit priority.
- Use mask-and-set for DSI_VID_PCK_TIME and DSI_VID_VCA_SETTING1
- Restore DSI_VID_VCA_SETTING2 field
  DSI_VID_VCA_SETTING2_MAX_LINE_LIMIT to blkline_pck - 6 as in
  the vendor driver and mask the field properly.
ChangeLog v3->v4:
- Calculate toward actual HS rate of the clock rather than the
  idealized rate provided by the panel resolution, this is what
  the vendor driver does.
- Add much comments and elaborate with references to the manual
  so the code can be understood as far as possible.
- Compared register dumps to that on the Samsung GT-I8190 (Golden)
  boot loader settings. We are now reasonably close to these,
  it may be that the boot loader driver is using slightly different
  settings for porches and syncs etc. But all figures makes sense.
- Duplicated the vendor code in a spread sheet and compared to
  what this code gives and we have an identical match with one
  small exception that the vendor code adds a small padding of 2
  lines to the vertical blanking area. This looks weird and might
  be some hackishly specified porch.
ChangeLog v2->v3:
- Rename the "bpp" variable to "cpp" since it is "chars per pixel"
  this was confusingly named in the vendor driver and it got
  carried over.
- Assign the SETTING2_EXACT_BURST_LIMIT by first shifting
  then masking.
- Also mask with the inverse of DSI_VID_BLKSIZE1_BLKEOL_PCK_MASK
  before writing blkeol into DSI_VID_BLKSIZE1, so we make sure
  to zero these bits first.
- Also mask with DSI_VID_BLKSIZE1_BLKLINE_EVENT_PCK_MASK
  when writing event package length.
- Comb through the code and compare it to vendor code and try
  to get closer to doing what the vendor driver is doing.
ChangeLog v1->v2:
- Fix some more comments so we understand what is going on.
- Set up the maximum line limit size in the right register
  instead of setting it in the burst size register portion.
- Set some default wakeup time other than zero (still need
  fixing more).
---
 drivers/gpu/drm/mcde/mcde_dsi.c      | 239 +++++++++++++++++++++------
 drivers/gpu/drm/mcde/mcde_dsi_regs.h |   1 +
 2 files changed, 192 insertions(+), 48 deletions(-)

-- 
2.21.0

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Comments

Stephan Gerhold Dec. 17, 2019, 5:48 p.m. | #1
On Tue, Dec 17, 2019 at 04:09:59PM +0100, Linus Walleij wrote:
> The video DSI mode had not really been tested. These fixes makes

> it more likely to work on real hardware:

> - Put the active width (x width) in the right bits and the VSA

>   (vertical sync active) in the right bits (those were swapped).

> - Calculate the packet sizes in bytes as in the vendor driver,

>   rather than in bits. Test the calculations agains a

>   spreadsheet and confirmed by debug prints to be reasonable.

> - Also verified the register values with relative confidence

>   to register dumps from the Samsung GT-I8190 boot loader

>   graphics. We are not identical but not off by far either.

> - Error out if the current mode and refresh frequency doesn't

>   work out. (In the future we may simply want to scale down

>   the vrefresh.)

> - Handle negative result in front/back/sync packages and fall

>   back to zero like in the vendor driver.

> - Put in lots of clarifying comments and references to the

>   documentation where the code is hard to understand.

> - Set the DSI_VID_VCA_SETTING2 field

>   DSI_VID_VCA_SETTING2_MAX_LINE_LIMIT to blkline_pck - 6 as in

>   the vendor driver and mask the field properly.

> - Set the DSI_VID_VCA_SETTING1 field

>   DSI_VID_VCA_SETTING1_MAX_BURST_LIMIT to blkeol_pck - 6 to

>   blkeol_duration - 6 as in the vendor driver.

> 

> Cc: Stephan Gerhold <stephan@gerhold.net>

> Fixes: 5fc537bfd000 ("drm/mcde: Add new driver for ST-Ericsson MCDE")

> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>


Thanks for making all the changes!

I don't fully understand most of the calculations,
but it seems to match the code in the vendor kernel now. Therefore:

Reviewed-by: Stephan Gerhold <stephan@gerhold.net>


> ---

> ChangeLog v5->v6:

> - DSI_VID_VCA_SETTING1_MAX_BURST_LIMIT should be blkeol_pck - 6

>   not blkeol_duration - 6.

> - Parenthesize some calculations.

> ChangeLog v4->v5:

> - Restore log order, last verstion of the changelog inadvertedly

>   merged v3 and v4 into v3 since I thought I didn't send out v3...

> - Parens in blkeol_pck = bpl - (mode->htotal * cpp) - 6 for

>   explicit priority.

> - Use mask-and-set for DSI_VID_PCK_TIME and DSI_VID_VCA_SETTING1

> - Restore DSI_VID_VCA_SETTING2 field

>   DSI_VID_VCA_SETTING2_MAX_LINE_LIMIT to blkline_pck - 6 as in

>   the vendor driver and mask the field properly.

> ChangeLog v3->v4:

> - Calculate toward actual HS rate of the clock rather than the

>   idealized rate provided by the panel resolution, this is what

>   the vendor driver does.

> - Add much comments and elaborate with references to the manual

>   so the code can be understood as far as possible.

> - Compared register dumps to that on the Samsung GT-I8190 (Golden)

>   boot loader settings. We are now reasonably close to these,

>   it may be that the boot loader driver is using slightly different

>   settings for porches and syncs etc. But all figures makes sense.

> - Duplicated the vendor code in a spread sheet and compared to

>   what this code gives and we have an identical match with one

>   small exception that the vendor code adds a small padding of 2

>   lines to the vertical blanking area. This looks weird and might

>   be some hackishly specified porch.

> ChangeLog v2->v3:

> - Rename the "bpp" variable to "cpp" since it is "chars per pixel"

>   this was confusingly named in the vendor driver and it got

>   carried over.

> - Assign the SETTING2_EXACT_BURST_LIMIT by first shifting

>   then masking.

> - Also mask with the inverse of DSI_VID_BLKSIZE1_BLKEOL_PCK_MASK

>   before writing blkeol into DSI_VID_BLKSIZE1, so we make sure

>   to zero these bits first.

> - Also mask with DSI_VID_BLKSIZE1_BLKLINE_EVENT_PCK_MASK

>   when writing event package length.

> - Comb through the code and compare it to vendor code and try

>   to get closer to doing what the vendor driver is doing.

> ChangeLog v1->v2:

> - Fix some more comments so we understand what is going on.

> - Set up the maximum line limit size in the right register

>   instead of setting it in the burst size register portion.

> - Set some default wakeup time other than zero (still need

>   fixing more).

> ---

>  drivers/gpu/drm/mcde/mcde_dsi.c      | 239 +++++++++++++++++++++------

>  drivers/gpu/drm/mcde/mcde_dsi_regs.h |   1 +

>  2 files changed, 192 insertions(+), 48 deletions(-)

> 

> diff --git a/drivers/gpu/drm/mcde/mcde_dsi.c b/drivers/gpu/drm/mcde/mcde_dsi.c

> index 21cee4d9d2fd..6613c68c0633 100644

> --- a/drivers/gpu/drm/mcde/mcde_dsi.c

> +++ b/drivers/gpu/drm/mcde/mcde_dsi.c

> @@ -379,13 +379,14 @@ void mcde_dsi_te_request(struct mipi_dsi_device *mdsi)

>  static void mcde_dsi_setup_video_mode(struct mcde_dsi *d,

>  				      const struct drm_display_mode *mode)

>  {

> -	u8 bpp = mipi_dsi_pixel_format_to_bpp(d->mdsi->format);

> +	/* cpp, characters per pixel, number of bytes per pixel */

> +	u8 cpp = mipi_dsi_pixel_format_to_bpp(d->mdsi->format) / 8;

> +	u64 pclk;

>  	u64 bpl;

> -	u32 hfp;

> -	u32 hbp;

> -	u32 hsa;

> +	int hfp;

> +	int hbp;

> +	int hsa;

>  	u32 blkline_pck, line_duration;

> -	u32 blkeol_pck, blkeol_duration;

>  	u32 val;

>  

>  	val = 0;

> @@ -422,11 +423,21 @@ static void mcde_dsi_setup_video_mode(struct mcde_dsi *d,

>  		return;

>  	}

>  

> -	/* TODO: TVG could be enabled here */

> +	/* TODO: TVG (test video generator) could be enabled here */

>  

> -	/* Send blanking packet */

> +	/*

> +	 * During vertical blanking: go to LP mode

> +	 * Like with the EOL setting, if this is not set, the EOL area will be

> +	 * filled with NULL or blanking packets in the vblank area.

> +	 * FIXME: some Samsung phones and display panels such as s6e63m0 use

> +	 * DSI_VID_MAIN_CTL_REG_BLKLINE_MODE_BLANKING here instead,

> +	 * figure out how to properly configure that from the panel.

> +	 */

>  	val |= DSI_VID_MAIN_CTL_REG_BLKLINE_MODE_LP_0;

> -	/* Send EOL packet */

> +	/*

> +	 * During EOL: go to LP mode. If this is not set, the EOL area will be

> +	 * filled with NULL or blanking packets.

> +	 */

>  	val |= DSI_VID_MAIN_CTL_REG_BLKEOL_MODE_LP_0;

>  	/* Recovery mode 1 */

>  	val |= 1 << DSI_VID_MAIN_CTL_RECOVERY_MODE_SHIFT;

> @@ -434,13 +445,13 @@ static void mcde_dsi_setup_video_mode(struct mcde_dsi *d,

>  	writel(val, d->regs + DSI_VID_MAIN_CTL);

>  

>  	/* Vertical frame parameters are pretty straight-forward */

> -	val = mode->vdisplay << DSI_VID_VSIZE_VSA_LENGTH_SHIFT;

> +	val = mode->vdisplay << DSI_VID_VSIZE_VACT_LENGTH_SHIFT;

>  	/* vertical front porch */

>  	val |= (mode->vsync_start - mode->vdisplay)

>  		<< DSI_VID_VSIZE_VFP_LENGTH_SHIFT;

>  	/* vertical sync active */

>  	val |= (mode->vsync_end - mode->vsync_start)

> -		<< DSI_VID_VSIZE_VACT_LENGTH_SHIFT;

> +		<< DSI_VID_VSIZE_VSA_LENGTH_SHIFT;

>  	/* vertical back porch */

>  	val |= (mode->vtotal - mode->vsync_end)

>  		<< DSI_VID_VSIZE_VBP_LENGTH_SHIFT;

> @@ -448,36 +459,54 @@ static void mcde_dsi_setup_video_mode(struct mcde_dsi *d,

>  

>  	/*

>  	 * Horizontal frame parameters:

> -	 * horizontal resolution is given in pixels and must be re-calculated

> -	 * into bytes since this is what the hardware expects.

> +	 * horizontal resolution is given in pixels but must be re-calculated

> +	 * into bytes since this is what the hardware expects, these registers

> +	 * define the payload size of the packet.

> +	 *

> +	 * hfp = horizontal front porch in bytes

> +	 * hbp = horizontal back porch in bytes

> +	 * hsa = horizontal sync active in bytes

>  	 *

>  	 * 6 + 2 is HFP header + checksum

>  	 */

> -	hfp = (mode->hsync_start - mode->hdisplay) * bpp - 6 - 2;

> +	hfp = (mode->hsync_start - mode->hdisplay) * cpp - 6 - 2;

>  	if (d->mdsi->mode_flags & MIPI_DSI_MODE_VIDEO_SYNC_PULSE) {

>  		/*

> +		 * Use sync pulse for sync: explicit HSA time

>  		 * 6 is HBP header + checksum

>  		 * 4 is RGB header + checksum

>  		 */

> -		hbp = (mode->htotal - mode->hsync_end) * bpp - 4 - 6;

> +		hbp = (mode->htotal - mode->hsync_end) * cpp - 4 - 6;

>  		/*

>  		 * 6 is HBP header + checksum

>  		 * 4 is HSW packet bytes

>  		 * 4 is RGB header + checksum

>  		 */

> -		hsa = (mode->hsync_end - mode->hsync_start) * bpp - 4 - 4 - 6;

> +		hsa = (mode->hsync_end - mode->hsync_start) * cpp - 4 - 4 - 6;

>  	} else {

>  		/*

> -		 * HBP includes both back porch and sync

> +		 * Use event for sync: HBP includes both back porch and sync

>  		 * 6 is HBP header + checksum

>  		 * 4 is HSW packet bytes

>  		 * 4 is RGB header + checksum

>  		 */

> -		hbp = (mode->htotal - mode->hsync_start) * bpp - 4 - 4 - 6;

> -		/* HSA is not considered in this mode and set to 0 */

> +		hbp = (mode->htotal - mode->hsync_start) * cpp - 4 - 4 - 6;

> +		/* HSA is not present in this mode and set to 0 */

> +		hsa = 0;

> +	}

> +	if (hfp < 0) {

> +		dev_info(d->dev, "hfp negative, set to 0\n");

> +		hfp = 0;

> +	}

> +	if (hbp < 0) {

> +		dev_info(d->dev, "hbp negative, set to 0\n");

> +		hbp = 0;

> +	}

> +	if (hsa < 0) {

> +		dev_info(d->dev, "hsa negative, set to 0\n");

>  		hsa = 0;

>  	}

> -	dev_dbg(d->dev, "hfp: %u, hbp: %u, hsa: %u\n",

> +	dev_dbg(d->dev, "hfp: %u, hbp: %u, hsa: %u bytes\n",

>  		hfp, hbp, hsa);

>  

>  	/* Frame parameters: horizontal sync active */

> @@ -488,71 +517,185 @@ static void mcde_dsi_setup_video_mode(struct mcde_dsi *d,

>  	val |= hfp << DSI_VID_HSIZE1_HFP_LENGTH_SHIFT;

>  	writel(val, d->regs + DSI_VID_HSIZE1);

>  

> -	/* RGB data length (bytes on one scanline) */

> -	val = mode->hdisplay * (bpp / 8);

> +	/* RGB data length (visible bytes on one scanline) */

> +	val = mode->hdisplay * cpp;

>  	writel(val, d->regs + DSI_VID_HSIZE2);

> +	dev_dbg(d->dev, "RGB length, visible area on a line: %u bytes\n", val);

>  

> -	/* TODO: further adjustments for TVG mode here */

> +	/*

> +	 * Calculate the time between two pixels in picoseconds using

> +	 * the supplied refresh rate and total resolution including

> +	 * porches and sync.

> +	 */

> +	/* (ps/s) / (pixels/s) = ps/pixels */

> +	pclk = DIV_ROUND_UP_ULL(1000000000000,

> +				(mode->vrefresh * mode->htotal * mode->vtotal));

> +	dev_dbg(d->dev, "picoseconds between two pixels: %llu\n",

> +		pclk);

>  

>  	/*

> -	 * EOL packet length from bits per line calculations: pixel clock

> -	 * is given in kHz, calculate the time between two pixels in

> -	 * picoseconds.

> +	 * How many bytes per line will this update frequency yield?

> +	 *

> +	 * Calculate the number of picoseconds for one scanline (1), then

> +	 * divide by 1000000000000 (2) to get in pixels per second we

> +	 * want to output.

> +	 *

> +	 * Multiply with number of bytes per second at this video display

> +	 * frequency (3) to get number of bytes transferred during this

> +	 * time. Notice that we use the frequency the display wants,

> +	 * not what we actually get from the DSI PLL, which is hs_freq.

> +	 *

> +	 * These arithmetics are done in a different order to avoid

> +	 * overflow.

>  	 */

> -	bpl = mode->clock * mode->htotal;

> -	bpl *= (d->hs_freq / 8);

> -	do_div(bpl, 1000000); /* microseconds */

> -	do_div(bpl, 1000000); /* seconds */

> +	bpl = pclk * mode->htotal; /* (1) picoseconds per line */

> +	dev_dbg(d->dev, "picoseconds per line: %llu\n", bpl);

> +	/* Multiply with bytes per second (3) */

> +	bpl *= (d->mdsi->hs_rate / 8);

> +	/* Pixels per second (2) */

> +	bpl = DIV_ROUND_DOWN_ULL(bpl, 1000000); /* microseconds */

> +	bpl = DIV_ROUND_DOWN_ULL(bpl, 1000000); /* seconds */

> +	/* parallel transactions in all lanes */

>  	bpl *= d->mdsi->lanes;

> -	dev_dbg(d->dev, "calculated bytes per line: %llu\n", bpl);

> +	dev_dbg(d->dev,

> +		"calculated bytes per line: %llu @ %d Hz with HS %lu Hz\n",

> +		bpl, mode->vrefresh, d->mdsi->hs_rate);

> +

>  	/*

>  	 * 6 is header + checksum, header = 4 bytes, checksum = 2 bytes

>  	 * 4 is short packet for vsync/hsync

>  	 */

>  	if (d->mdsi->mode_flags & MIPI_DSI_MODE_VIDEO_SYNC_PULSE) {

> -		/* Fixme: isn't the hsync width in pixels? */

> +		/* Set the event packet size to 0 (not used) */

> +		writel(0, d->regs + DSI_VID_BLKSIZE1);

> +		/*

> +		 * FIXME: isn't the hsync width in pixels? The porch and

> +		 * sync area size is in pixels here, but this -6

> +		 * seems to be for bytes. It looks like this in the vendor

> +		 * code though. Is it completely untested?

> +		 */

>  		blkline_pck = bpl - (mode->hsync_end - mode->hsync_start) - 6;

>  		val = blkline_pck << DSI_VID_BLKSIZE2_BLKLINE_PULSE_PCK_SHIFT;

>  		writel(val, d->regs + DSI_VID_BLKSIZE2);

>  	} else {

> +		/* Set the sync pulse packet size to 0 (not used) */

> +		writel(0, d->regs + DSI_VID_BLKSIZE2);

> +		/* Specifying payload size in bytes (-4-6 from manual) */

>  		blkline_pck = bpl - 4 - 6;

> +		if (blkline_pck > 0x1FFF)

> +			dev_err(d->dev, "blkline_pck too big %d bytes\n",

> +				blkline_pck);

>  		val = blkline_pck << DSI_VID_BLKSIZE1_BLKLINE_EVENT_PCK_SHIFT;

> +		val &= DSI_VID_BLKSIZE1_BLKLINE_EVENT_PCK_MASK;

>  		writel(val, d->regs + DSI_VID_BLKSIZE1);

>  	}

>  

> -	line_duration = (blkline_pck + 6) / d->mdsi->lanes;

> -	dev_dbg(d->dev, "line duration %u\n", line_duration);

> +	/*

> +	 * The line duration is used to scale back the frequency from

> +	 * the max frequency supported by the HS clock to the desired

> +	 * update frequency in vrefresh.

> +	 */

> +	line_duration = blkline_pck + 6;

> +	/*

> +	 * The datasheet contains this complex condition to decreasing

> +	 * the line duration by 1 under very specific circumstances.

> +	 * Here we also imply that LP is used during burst EOL.

> +	 */

> +	if (d->mdsi->lanes == 2 && (hsa & 0x01) && (hfp & 0x01)

> +	    && (d->mdsi->mode_flags & MIPI_DSI_MODE_VIDEO_BURST))

> +		line_duration--;

> +	line_duration = DIV_ROUND_CLOSEST(line_duration, d->mdsi->lanes);

> +	dev_dbg(d->dev, "line duration %u bytes\n", line_duration);

>  	val = line_duration << DSI_VID_DPHY_TIME_REG_LINE_DURATION_SHIFT;

>  	/*

>  	 * This is the time to perform LP->HS on D-PHY

>  	 * FIXME: nowhere to get this from: DT property on the DSI?

> +	 * The manual says this is "system dependent".

> +	 * values like 48 and 72 seen in the vendor code.

>  	 */

> -	val |= 0 << DSI_VID_DPHY_TIME_REG_WAKEUP_TIME_SHIFT;

> +	val |= 48 << DSI_VID_DPHY_TIME_REG_WAKEUP_TIME_SHIFT;

>  	writel(val, d->regs + DSI_VID_DPHY_TIME);

>  

> -	/* Calculate block end of line */

> -	blkeol_pck = bpl - mode->hdisplay * bpp - 6;

> -	blkeol_duration = (blkeol_pck + 6) / d->mdsi->lanes;

> -	dev_dbg(d->dev, "blkeol pck: %u, duration: %u\n",

> -		 blkeol_pck, blkeol_duration);

> -

> +	/*

> +	 * See the manual figure 657 page 2203 for understanding the impact

> +	 * of the different burst mode settings.

> +	 */

>  	if (d->mdsi->mode_flags & MIPI_DSI_MODE_VIDEO_BURST) {

> -		/* Set up EOL clock for burst mode */

> +		int blkeol_pck, blkeol_duration;

> +		/*

> +		 * Packet size at EOL for burst mode, this is only used

> +		 * if DSI_VID_MAIN_CTL_REG_BLKEOL_MODE_LP_0 is NOT set,

> +		 * but we instead send NULL or blanking packets at EOL.

> +		 * This is given in number of bytes.

> +		 *

> +		 * See the manual page 2198 for the 13 reg_blkeol_pck bits.

> +		 */

> +		blkeol_pck = bpl - (mode->htotal * cpp) - 6;

> +		if (blkeol_pck < 0) {

> +			dev_err(d->dev, "video block does not fit on line!\n");

> +			dev_err(d->dev,

> +				"calculated bytes per line: %llu @ %d Hz\n",

> +				bpl, mode->vrefresh);

> +			dev_err(d->dev,

> +				"bytes per line (blkline_pck) %u bytes\n",

> +				blkline_pck);

> +			dev_err(d->dev,

> +				"blkeol_pck becomes %d bytes\n", blkeol_pck);

> +			return;

> +		}

> +		dev_dbg(d->dev, "BLKEOL packet: %d bytes\n", blkeol_pck);

> +

>  		val = readl(d->regs + DSI_VID_BLKSIZE1);

> +		val &= ~DSI_VID_BLKSIZE1_BLKEOL_PCK_MASK;

>  		val |= blkeol_pck << DSI_VID_BLKSIZE1_BLKEOL_PCK_SHIFT;

>  		writel(val, d->regs + DSI_VID_BLKSIZE1);

> -		writel(blkeol_pck, d->regs + DSI_VID_VCA_SETTING2);

> -

> -		writel(blkeol_duration, d->regs + DSI_VID_PCK_TIME);

> -		writel(blkeol_duration - 6, d->regs + DSI_VID_VCA_SETTING1);

> +		/* Use the same value for exact burst limit */

> +		val = blkeol_pck <<

> +			DSI_VID_VCA_SETTING2_EXACT_BURST_LIMIT_SHIFT;

> +		val &= DSI_VID_VCA_SETTING2_EXACT_BURST_LIMIT_MASK;

> +		writel(val, d->regs + DSI_VID_VCA_SETTING2);

> +		/*

> +		 * This BLKEOL duration is claimed to be the duration in clock

> +		 * cycles of the BLLP end-of-line (EOL) period for each line if

> +		 * DSI_VID_MAIN_CTL_REG_BLKEOL_MODE_LP_0 is set.

> +		 *

> +		 * It is hard to trust the manuals' claim that this is in clock

> +		 * cycles as we mimic the behaviour of the vendor code, which

> +		 * appears to write a number of bytes that would have been

> +		 * transferred on a single lane.

> +		 *

> +		 * See the manual figure 657 page 2203 and page 2198 for the 13

> +		 * reg_blkeol_duration bits.

> +		 *

> +		 * FIXME: should this also be set up also for non-burst mode

> +		 * according to figure 565 page 2202?

> +		 */

> +		blkeol_duration = DIV_ROUND_CLOSEST(blkeol_pck + 6,

> +						    d->mdsi->lanes);

> +		dev_dbg(d->dev, "BLKEOL duration: %d clock cycles\n",

> +			blkeol_duration);

> +

> +		val = readl(d->regs + DSI_VID_PCK_TIME);

> +		val &= ~DSI_VID_PCK_TIME_BLKEOL_DURATION_MASK;

> +		val |= blkeol_duration <<

> +			DSI_VID_PCK_TIME_BLKEOL_DURATION_SHIFT;

> +		writel(val, d->regs + DSI_VID_PCK_TIME);

> +

> +		/* Max burst limit, this is given in bytes */

> +		val = readl(d->regs + DSI_VID_VCA_SETTING1);

> +		val &= ~DSI_VID_VCA_SETTING1_MAX_BURST_LIMIT_MASK;

> +		val |= (blkeol_pck - 6) <<

> +			DSI_VID_VCA_SETTING1_MAX_BURST_LIMIT_SHIFT;

> +		writel(val, d->regs + DSI_VID_VCA_SETTING1);

>  	}

>  

>  	/* Maximum line limit */

>  	val = readl(d->regs + DSI_VID_VCA_SETTING2);

> -	val |= blkline_pck <<

> -		DSI_VID_VCA_SETTING2_EXACT_BURST_LIMIT_SHIFT;

> +	val &= ~DSI_VID_VCA_SETTING2_MAX_LINE_LIMIT_MASK;

> +	val |= (blkline_pck - 6) <<

> +		DSI_VID_VCA_SETTING2_MAX_LINE_LIMIT_SHIFT;

>  	writel(val, d->regs + DSI_VID_VCA_SETTING2);

> -

> +	dev_dbg(d->dev, "blkline pck: %d bytes\n", blkline_pck - 6);

>  }

>  

>  static void mcde_dsi_start(struct mcde_dsi *d)

> diff --git a/drivers/gpu/drm/mcde/mcde_dsi_regs.h b/drivers/gpu/drm/mcde/mcde_dsi_regs.h

> index 8089db805c57..16551af1089e 100644

> --- a/drivers/gpu/drm/mcde/mcde_dsi_regs.h

> +++ b/drivers/gpu/drm/mcde/mcde_dsi_regs.h

> @@ -228,6 +228,7 @@

>  

>  #define DSI_VID_PCK_TIME 0x000000A8

>  #define DSI_VID_PCK_TIME_BLKEOL_DURATION_SHIFT 0

> +#define DSI_VID_PCK_TIME_BLKEOL_DURATION_MASK 0x00000FFF

>  

>  #define DSI_VID_DPHY_TIME 0x000000AC

>  #define DSI_VID_DPHY_TIME_REG_LINE_DURATION_SHIFT 0

> -- 

> 2.21.0

> 

_______________________________________________
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Patch

diff --git a/drivers/gpu/drm/mcde/mcde_dsi.c b/drivers/gpu/drm/mcde/mcde_dsi.c
index 21cee4d9d2fd..6613c68c0633 100644
--- a/drivers/gpu/drm/mcde/mcde_dsi.c
+++ b/drivers/gpu/drm/mcde/mcde_dsi.c
@@ -379,13 +379,14 @@  void mcde_dsi_te_request(struct mipi_dsi_device *mdsi)
 static void mcde_dsi_setup_video_mode(struct mcde_dsi *d,
 				      const struct drm_display_mode *mode)
 {
-	u8 bpp = mipi_dsi_pixel_format_to_bpp(d->mdsi->format);
+	/* cpp, characters per pixel, number of bytes per pixel */
+	u8 cpp = mipi_dsi_pixel_format_to_bpp(d->mdsi->format) / 8;
+	u64 pclk;
 	u64 bpl;
-	u32 hfp;
-	u32 hbp;
-	u32 hsa;
+	int hfp;
+	int hbp;
+	int hsa;
 	u32 blkline_pck, line_duration;
-	u32 blkeol_pck, blkeol_duration;
 	u32 val;
 
 	val = 0;
@@ -422,11 +423,21 @@  static void mcde_dsi_setup_video_mode(struct mcde_dsi *d,
 		return;
 	}
 
-	/* TODO: TVG could be enabled here */
+	/* TODO: TVG (test video generator) could be enabled here */
 
-	/* Send blanking packet */
+	/*
+	 * During vertical blanking: go to LP mode
+	 * Like with the EOL setting, if this is not set, the EOL area will be
+	 * filled with NULL or blanking packets in the vblank area.
+	 * FIXME: some Samsung phones and display panels such as s6e63m0 use
+	 * DSI_VID_MAIN_CTL_REG_BLKLINE_MODE_BLANKING here instead,
+	 * figure out how to properly configure that from the panel.
+	 */
 	val |= DSI_VID_MAIN_CTL_REG_BLKLINE_MODE_LP_0;
-	/* Send EOL packet */
+	/*
+	 * During EOL: go to LP mode. If this is not set, the EOL area will be
+	 * filled with NULL or blanking packets.
+	 */
 	val |= DSI_VID_MAIN_CTL_REG_BLKEOL_MODE_LP_0;
 	/* Recovery mode 1 */
 	val |= 1 << DSI_VID_MAIN_CTL_RECOVERY_MODE_SHIFT;
@@ -434,13 +445,13 @@  static void mcde_dsi_setup_video_mode(struct mcde_dsi *d,
 	writel(val, d->regs + DSI_VID_MAIN_CTL);
 
 	/* Vertical frame parameters are pretty straight-forward */
-	val = mode->vdisplay << DSI_VID_VSIZE_VSA_LENGTH_SHIFT;
+	val = mode->vdisplay << DSI_VID_VSIZE_VACT_LENGTH_SHIFT;
 	/* vertical front porch */
 	val |= (mode->vsync_start - mode->vdisplay)
 		<< DSI_VID_VSIZE_VFP_LENGTH_SHIFT;
 	/* vertical sync active */
 	val |= (mode->vsync_end - mode->vsync_start)
-		<< DSI_VID_VSIZE_VACT_LENGTH_SHIFT;
+		<< DSI_VID_VSIZE_VSA_LENGTH_SHIFT;
 	/* vertical back porch */
 	val |= (mode->vtotal - mode->vsync_end)
 		<< DSI_VID_VSIZE_VBP_LENGTH_SHIFT;
@@ -448,36 +459,54 @@  static void mcde_dsi_setup_video_mode(struct mcde_dsi *d,
 
 	/*
 	 * Horizontal frame parameters:
-	 * horizontal resolution is given in pixels and must be re-calculated
-	 * into bytes since this is what the hardware expects.
+	 * horizontal resolution is given in pixels but must be re-calculated
+	 * into bytes since this is what the hardware expects, these registers
+	 * define the payload size of the packet.
+	 *
+	 * hfp = horizontal front porch in bytes
+	 * hbp = horizontal back porch in bytes
+	 * hsa = horizontal sync active in bytes
 	 *
 	 * 6 + 2 is HFP header + checksum
 	 */
-	hfp = (mode->hsync_start - mode->hdisplay) * bpp - 6 - 2;
+	hfp = (mode->hsync_start - mode->hdisplay) * cpp - 6 - 2;
 	if (d->mdsi->mode_flags & MIPI_DSI_MODE_VIDEO_SYNC_PULSE) {
 		/*
+		 * Use sync pulse for sync: explicit HSA time
 		 * 6 is HBP header + checksum
 		 * 4 is RGB header + checksum
 		 */
-		hbp = (mode->htotal - mode->hsync_end) * bpp - 4 - 6;
+		hbp = (mode->htotal - mode->hsync_end) * cpp - 4 - 6;
 		/*
 		 * 6 is HBP header + checksum
 		 * 4 is HSW packet bytes
 		 * 4 is RGB header + checksum
 		 */
-		hsa = (mode->hsync_end - mode->hsync_start) * bpp - 4 - 4 - 6;
+		hsa = (mode->hsync_end - mode->hsync_start) * cpp - 4 - 4 - 6;
 	} else {
 		/*
-		 * HBP includes both back porch and sync
+		 * Use event for sync: HBP includes both back porch and sync
 		 * 6 is HBP header + checksum
 		 * 4 is HSW packet bytes
 		 * 4 is RGB header + checksum
 		 */
-		hbp = (mode->htotal - mode->hsync_start) * bpp - 4 - 4 - 6;
-		/* HSA is not considered in this mode and set to 0 */
+		hbp = (mode->htotal - mode->hsync_start) * cpp - 4 - 4 - 6;
+		/* HSA is not present in this mode and set to 0 */
+		hsa = 0;
+	}
+	if (hfp < 0) {
+		dev_info(d->dev, "hfp negative, set to 0\n");
+		hfp = 0;
+	}
+	if (hbp < 0) {
+		dev_info(d->dev, "hbp negative, set to 0\n");
+		hbp = 0;
+	}
+	if (hsa < 0) {
+		dev_info(d->dev, "hsa negative, set to 0\n");
 		hsa = 0;
 	}
-	dev_dbg(d->dev, "hfp: %u, hbp: %u, hsa: %u\n",
+	dev_dbg(d->dev, "hfp: %u, hbp: %u, hsa: %u bytes\n",
 		hfp, hbp, hsa);
 
 	/* Frame parameters: horizontal sync active */
@@ -488,71 +517,185 @@  static void mcde_dsi_setup_video_mode(struct mcde_dsi *d,
 	val |= hfp << DSI_VID_HSIZE1_HFP_LENGTH_SHIFT;
 	writel(val, d->regs + DSI_VID_HSIZE1);
 
-	/* RGB data length (bytes on one scanline) */
-	val = mode->hdisplay * (bpp / 8);
+	/* RGB data length (visible bytes on one scanline) */
+	val = mode->hdisplay * cpp;
 	writel(val, d->regs + DSI_VID_HSIZE2);
+	dev_dbg(d->dev, "RGB length, visible area on a line: %u bytes\n", val);
 
-	/* TODO: further adjustments for TVG mode here */
+	/*
+	 * Calculate the time between two pixels in picoseconds using
+	 * the supplied refresh rate and total resolution including
+	 * porches and sync.
+	 */
+	/* (ps/s) / (pixels/s) = ps/pixels */
+	pclk = DIV_ROUND_UP_ULL(1000000000000,
+				(mode->vrefresh * mode->htotal * mode->vtotal));
+	dev_dbg(d->dev, "picoseconds between two pixels: %llu\n",
+		pclk);
 
 	/*
-	 * EOL packet length from bits per line calculations: pixel clock
-	 * is given in kHz, calculate the time between two pixels in
-	 * picoseconds.
+	 * How many bytes per line will this update frequency yield?
+	 *
+	 * Calculate the number of picoseconds for one scanline (1), then
+	 * divide by 1000000000000 (2) to get in pixels per second we
+	 * want to output.
+	 *
+	 * Multiply with number of bytes per second at this video display
+	 * frequency (3) to get number of bytes transferred during this
+	 * time. Notice that we use the frequency the display wants,
+	 * not what we actually get from the DSI PLL, which is hs_freq.
+	 *
+	 * These arithmetics are done in a different order to avoid
+	 * overflow.
 	 */
-	bpl = mode->clock * mode->htotal;
-	bpl *= (d->hs_freq / 8);
-	do_div(bpl, 1000000); /* microseconds */
-	do_div(bpl, 1000000); /* seconds */
+	bpl = pclk * mode->htotal; /* (1) picoseconds per line */
+	dev_dbg(d->dev, "picoseconds per line: %llu\n", bpl);
+	/* Multiply with bytes per second (3) */
+	bpl *= (d->mdsi->hs_rate / 8);
+	/* Pixels per second (2) */
+	bpl = DIV_ROUND_DOWN_ULL(bpl, 1000000); /* microseconds */
+	bpl = DIV_ROUND_DOWN_ULL(bpl, 1000000); /* seconds */
+	/* parallel transactions in all lanes */
 	bpl *= d->mdsi->lanes;
-	dev_dbg(d->dev, "calculated bytes per line: %llu\n", bpl);
+	dev_dbg(d->dev,
+		"calculated bytes per line: %llu @ %d Hz with HS %lu Hz\n",
+		bpl, mode->vrefresh, d->mdsi->hs_rate);
+
 	/*
 	 * 6 is header + checksum, header = 4 bytes, checksum = 2 bytes
 	 * 4 is short packet for vsync/hsync
 	 */
 	if (d->mdsi->mode_flags & MIPI_DSI_MODE_VIDEO_SYNC_PULSE) {
-		/* Fixme: isn't the hsync width in pixels? */
+		/* Set the event packet size to 0 (not used) */
+		writel(0, d->regs + DSI_VID_BLKSIZE1);
+		/*
+		 * FIXME: isn't the hsync width in pixels? The porch and
+		 * sync area size is in pixels here, but this -6
+		 * seems to be for bytes. It looks like this in the vendor
+		 * code though. Is it completely untested?
+		 */
 		blkline_pck = bpl - (mode->hsync_end - mode->hsync_start) - 6;
 		val = blkline_pck << DSI_VID_BLKSIZE2_BLKLINE_PULSE_PCK_SHIFT;
 		writel(val, d->regs + DSI_VID_BLKSIZE2);
 	} else {
+		/* Set the sync pulse packet size to 0 (not used) */
+		writel(0, d->regs + DSI_VID_BLKSIZE2);
+		/* Specifying payload size in bytes (-4-6 from manual) */
 		blkline_pck = bpl - 4 - 6;
+		if (blkline_pck > 0x1FFF)
+			dev_err(d->dev, "blkline_pck too big %d bytes\n",
+				blkline_pck);
 		val = blkline_pck << DSI_VID_BLKSIZE1_BLKLINE_EVENT_PCK_SHIFT;
+		val &= DSI_VID_BLKSIZE1_BLKLINE_EVENT_PCK_MASK;
 		writel(val, d->regs + DSI_VID_BLKSIZE1);
 	}
 
-	line_duration = (blkline_pck + 6) / d->mdsi->lanes;
-	dev_dbg(d->dev, "line duration %u\n", line_duration);
+	/*
+	 * The line duration is used to scale back the frequency from
+	 * the max frequency supported by the HS clock to the desired
+	 * update frequency in vrefresh.
+	 */
+	line_duration = blkline_pck + 6;
+	/*
+	 * The datasheet contains this complex condition to decreasing
+	 * the line duration by 1 under very specific circumstances.
+	 * Here we also imply that LP is used during burst EOL.
+	 */
+	if (d->mdsi->lanes == 2 && (hsa & 0x01) && (hfp & 0x01)
+	    && (d->mdsi->mode_flags & MIPI_DSI_MODE_VIDEO_BURST))
+		line_duration--;
+	line_duration = DIV_ROUND_CLOSEST(line_duration, d->mdsi->lanes);
+	dev_dbg(d->dev, "line duration %u bytes\n", line_duration);
 	val = line_duration << DSI_VID_DPHY_TIME_REG_LINE_DURATION_SHIFT;
 	/*
 	 * This is the time to perform LP->HS on D-PHY
 	 * FIXME: nowhere to get this from: DT property on the DSI?
+	 * The manual says this is "system dependent".
+	 * values like 48 and 72 seen in the vendor code.
 	 */
-	val |= 0 << DSI_VID_DPHY_TIME_REG_WAKEUP_TIME_SHIFT;
+	val |= 48 << DSI_VID_DPHY_TIME_REG_WAKEUP_TIME_SHIFT;
 	writel(val, d->regs + DSI_VID_DPHY_TIME);
 
-	/* Calculate block end of line */
-	blkeol_pck = bpl - mode->hdisplay * bpp - 6;
-	blkeol_duration = (blkeol_pck + 6) / d->mdsi->lanes;
-	dev_dbg(d->dev, "blkeol pck: %u, duration: %u\n",
-		 blkeol_pck, blkeol_duration);
-
+	/*
+	 * See the manual figure 657 page 2203 for understanding the impact
+	 * of the different burst mode settings.
+	 */
 	if (d->mdsi->mode_flags & MIPI_DSI_MODE_VIDEO_BURST) {
-		/* Set up EOL clock for burst mode */
+		int blkeol_pck, blkeol_duration;
+		/*
+		 * Packet size at EOL for burst mode, this is only used
+		 * if DSI_VID_MAIN_CTL_REG_BLKEOL_MODE_LP_0 is NOT set,
+		 * but we instead send NULL or blanking packets at EOL.
+		 * This is given in number of bytes.
+		 *
+		 * See the manual page 2198 for the 13 reg_blkeol_pck bits.
+		 */
+		blkeol_pck = bpl - (mode->htotal * cpp) - 6;
+		if (blkeol_pck < 0) {
+			dev_err(d->dev, "video block does not fit on line!\n");
+			dev_err(d->dev,
+				"calculated bytes per line: %llu @ %d Hz\n",
+				bpl, mode->vrefresh);
+			dev_err(d->dev,
+				"bytes per line (blkline_pck) %u bytes\n",
+				blkline_pck);
+			dev_err(d->dev,
+				"blkeol_pck becomes %d bytes\n", blkeol_pck);
+			return;
+		}
+		dev_dbg(d->dev, "BLKEOL packet: %d bytes\n", blkeol_pck);
+
 		val = readl(d->regs + DSI_VID_BLKSIZE1);
+		val &= ~DSI_VID_BLKSIZE1_BLKEOL_PCK_MASK;
 		val |= blkeol_pck << DSI_VID_BLKSIZE1_BLKEOL_PCK_SHIFT;
 		writel(val, d->regs + DSI_VID_BLKSIZE1);
-		writel(blkeol_pck, d->regs + DSI_VID_VCA_SETTING2);
-
-		writel(blkeol_duration, d->regs + DSI_VID_PCK_TIME);
-		writel(blkeol_duration - 6, d->regs + DSI_VID_VCA_SETTING1);
+		/* Use the same value for exact burst limit */
+		val = blkeol_pck <<
+			DSI_VID_VCA_SETTING2_EXACT_BURST_LIMIT_SHIFT;
+		val &= DSI_VID_VCA_SETTING2_EXACT_BURST_LIMIT_MASK;
+		writel(val, d->regs + DSI_VID_VCA_SETTING2);
+		/*
+		 * This BLKEOL duration is claimed to be the duration in clock
+		 * cycles of the BLLP end-of-line (EOL) period for each line if
+		 * DSI_VID_MAIN_CTL_REG_BLKEOL_MODE_LP_0 is set.
+		 *
+		 * It is hard to trust the manuals' claim that this is in clock
+		 * cycles as we mimic the behaviour of the vendor code, which
+		 * appears to write a number of bytes that would have been
+		 * transferred on a single lane.
+		 *
+		 * See the manual figure 657 page 2203 and page 2198 for the 13
+		 * reg_blkeol_duration bits.
+		 *
+		 * FIXME: should this also be set up also for non-burst mode
+		 * according to figure 565 page 2202?
+		 */
+		blkeol_duration = DIV_ROUND_CLOSEST(blkeol_pck + 6,
+						    d->mdsi->lanes);
+		dev_dbg(d->dev, "BLKEOL duration: %d clock cycles\n",
+			blkeol_duration);
+
+		val = readl(d->regs + DSI_VID_PCK_TIME);
+		val &= ~DSI_VID_PCK_TIME_BLKEOL_DURATION_MASK;
+		val |= blkeol_duration <<
+			DSI_VID_PCK_TIME_BLKEOL_DURATION_SHIFT;
+		writel(val, d->regs + DSI_VID_PCK_TIME);
+
+		/* Max burst limit, this is given in bytes */
+		val = readl(d->regs + DSI_VID_VCA_SETTING1);
+		val &= ~DSI_VID_VCA_SETTING1_MAX_BURST_LIMIT_MASK;
+		val |= (blkeol_pck - 6) <<
+			DSI_VID_VCA_SETTING1_MAX_BURST_LIMIT_SHIFT;
+		writel(val, d->regs + DSI_VID_VCA_SETTING1);
 	}
 
 	/* Maximum line limit */
 	val = readl(d->regs + DSI_VID_VCA_SETTING2);
-	val |= blkline_pck <<
-		DSI_VID_VCA_SETTING2_EXACT_BURST_LIMIT_SHIFT;
+	val &= ~DSI_VID_VCA_SETTING2_MAX_LINE_LIMIT_MASK;
+	val |= (blkline_pck - 6) <<
+		DSI_VID_VCA_SETTING2_MAX_LINE_LIMIT_SHIFT;
 	writel(val, d->regs + DSI_VID_VCA_SETTING2);
-
+	dev_dbg(d->dev, "blkline pck: %d bytes\n", blkline_pck - 6);
 }
 
 static void mcde_dsi_start(struct mcde_dsi *d)
diff --git a/drivers/gpu/drm/mcde/mcde_dsi_regs.h b/drivers/gpu/drm/mcde/mcde_dsi_regs.h
index 8089db805c57..16551af1089e 100644
--- a/drivers/gpu/drm/mcde/mcde_dsi_regs.h
+++ b/drivers/gpu/drm/mcde/mcde_dsi_regs.h
@@ -228,6 +228,7 @@ 
 
 #define DSI_VID_PCK_TIME 0x000000A8
 #define DSI_VID_PCK_TIME_BLKEOL_DURATION_SHIFT 0
+#define DSI_VID_PCK_TIME_BLKEOL_DURATION_MASK 0x00000FFF
 
 #define DSI_VID_DPHY_TIME 0x000000AC
 #define DSI_VID_DPHY_TIME_REG_LINE_DURATION_SHIFT 0