[3/3] drm/pl111: Use max memory bandwidth for resolution

Message ID 20180206121854.4407-4-linus.walleij@linaro.org
State Superseded
Headers show
Series
  • Bandwidth limitation on PL111, take 2
Related show

Commit Message

Linus Walleij Feb. 6, 2018, 12:18 p.m.
We were previously selecting 1024x768 and 32BPP as the default
set-up for the PL111 consumers.

This does not work on elder systems: the device tree bindings
support a property "max-memory-bandwidth" in bytes/second that
states that if you exceed this the memory bus will saturate.
The result is flickering and unstable images.

Parse the "max-memory-bandwidth" and respect it when
intializing the driver. On the RealView PB11MP, Versatile and
Integrator/CP we get a nice console as default with this code.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
ChangeLog v1->v2:
- Exploit the new .mode_valid() callback we added to the
  simple KMS helper.
- Use the hardcoded bits per pixel per variant instead of
  trying to be heuristic about this setting for now.
---
 drivers/gpu/drm/pl111/pl111_display.c | 30 ++++++++++++++++++++++++++++++
 drivers/gpu/drm/pl111/pl111_drm.h     |  1 +
 drivers/gpu/drm/pl111/pl111_drv.c     |  6 ++++++
 3 files changed, 37 insertions(+)

Comments

Eric Anholt Feb. 10, 2018, 5:14 p.m. | #1
Linus Walleij <linus.walleij@linaro.org> writes:

> We were previously selecting 1024x768 and 32BPP as the default

> set-up for the PL111 consumers.

>

> This does not work on elder systems: the device tree bindings

> support a property "max-memory-bandwidth" in bytes/second that

> states that if you exceed this the memory bus will saturate.

> The result is flickering and unstable images.

>

> Parse the "max-memory-bandwidth" and respect it when

> intializing the driver. On the RealView PB11MP, Versatile and

> Integrator/CP we get a nice console as default with this code.

>

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

> ---

> ChangeLog v1->v2:

> - Exploit the new .mode_valid() callback we added to the

>   simple KMS helper.

> - Use the hardcoded bits per pixel per variant instead of

>   trying to be heuristic about this setting for now.

> ---

>  drivers/gpu/drm/pl111/pl111_display.c | 30 ++++++++++++++++++++++++++++++

>  drivers/gpu/drm/pl111/pl111_drm.h     |  1 +

>  drivers/gpu/drm/pl111/pl111_drv.c     |  6 ++++++

>  3 files changed, 37 insertions(+)

>

> diff --git a/drivers/gpu/drm/pl111/pl111_display.c b/drivers/gpu/drm/pl111/pl111_display.c

> index d75923896609..a1ca9e1ffe15 100644

> --- a/drivers/gpu/drm/pl111/pl111_display.c

> +++ b/drivers/gpu/drm/pl111/pl111_display.c

> @@ -50,6 +50,35 @@ irqreturn_t pl111_irq(int irq, void *data)

>  	return status;

>  }

>  

> +static enum drm_mode_status

> +pl111_mode_valid(struct drm_crtc *crtc,

> +		 const struct drm_display_mode *mode)

> +{

> +	struct drm_device *drm = crtc->dev;

> +	struct pl111_drm_dev_private *priv = drm->dev_private;

> +	u32 cpp = priv->variant->fb_bpp / 8;

> +	u64 bw;


Using the variant->fb_bpp for mode_valid checks here feels wrong to me
-- it means a larger mode wouldn't be considered valid on a
32bpp-preferred platform when 16bpp would make it work, and a 16bpp
platform will happily try to set a 32bpp mode that exceeds the
bandwidth.

On the other hand, if it makes things work most of the time I'm also
kind of OK with it.  Anyone else want to chime in here?

> +	/*

> +	 * We use the pixelclock to also account for interlaced modes, the

> +	 * resulting bandwidth is in bytes per second.

> +	 */

> +	bw = mode->clock * 1000; /* In Hz */

> +	bw = bw * mode->hdisplay * mode->vdisplay * cpp;

> +	bw = div_u64(bw, mode->htotal * mode->vtotal);

> +

> +	if (bw > priv->memory_bw) {

> +		DRM_DEBUG("%d x %d @ %d Hz, %d cpp, bw %llu too fast\n",

> +			  mode->hdisplay, mode->vdisplay, mode->clock, cpp, bw);

> +

> +		return MODE_BAD;

> +	}

> +	DRM_DEBUG("%d x %d @ %d Hz, %d cpp, bw %llu bytes/s OK\n",

> +		  mode->hdisplay, mode->vdisplay, mode->clock, cpp, bw);

> +

> +	return MODE_OK;

> +}


Maybe DRM_DEBUG_KMS for these?
Linus Walleij Feb. 11, 2018, 11:05 a.m. | #2
On Sat, Feb 10, 2018 at 6:14 PM, Eric Anholt <eric@anholt.net> wrote:
> Linus Walleij <linus.walleij@linaro.org> writes:

>> +static enum drm_mode_status
>> +pl111_mode_valid(struct drm_crtc *crtc,
>> +              const struct drm_display_mode *mode)
>> +{
>> +     struct drm_device *drm = crtc->dev;
>> +     struct pl111_drm_dev_private *priv = drm->dev_private;
>> +     u32 cpp = priv->variant->fb_bpp / 8;
>> +     u64 bw;
>
> Using the variant->fb_bpp for mode_valid checks here feels wrong to me
> -- it means a larger mode wouldn't be considered valid on a
> 32bpp-preferred platform when 16bpp would make it work, and a 16bpp
> platform will happily try to set a 32bpp mode that exceeds the
> bandwidth.

Yeah. So I have an additional patch (that I will send out with the
rest of the v2 patches) that actually go in and set ->fb_bpp to
16 on the RealViews to get some nice 1024x768 on these.

The other mode_valid() checks I've seen (well, OMAPDRM)
just assume 32bpp and goes on. I guess it is saved by not
supporting anything else.

> On the other hand, if it makes things work most of the time I'm also
> kind of OK with it.  Anyone else want to chime in here?

This makes things work but can be improved upon.

The core of the problem is that resolution is CRTC business
and seen as something limited by the monitor or
bridge/connector or so, then it calls this hook into the driver to
check that it can provide what the monitor/bridge/connector
suggests.

And then we have the opportunity to say we can't do such or
such resolution.

The pixel format on the other hand is seen as a display hardware
thing, so if I had an API here to call back into the driver and
restrict the formats to say 16bpp, I could confirm better
resolutions.

We can put that in place later and remove the ->fb_bpp if we
can chisel out the right API to set the pixel format.

I am working on another patch to set the preferred pixel format
instead of BPP when intiializing the framebuffer, so I will
investigate this at the same time, but I'd really like to build
on top of this code to avoid too many variables.

> Maybe DRM_DEBUG_KMS for these?

OK I fix :)

Yours,
Linus Walleij
Eric Anholt Feb. 22, 2018, 8:30 p.m. | #3
Linus Walleij <linus.walleij@linaro.org> writes:

> We were previously selecting 1024x768 and 32BPP as the default

> set-up for the PL111 consumers.

>

> This does not work on elder systems: the device tree bindings

> support a property "max-memory-bandwidth" in bytes/second that

> states that if you exceed this the memory bus will saturate.

> The result is flickering and unstable images.

>

> Parse the "max-memory-bandwidth" and respect it when

> intializing the driver. On the RealView PB11MP, Versatile and

> Integrator/CP we get a nice console as default with this code.

>

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

> ---

> ChangeLog v1->v2:

> - Exploit the new .mode_valid() callback we added to the

>   simple KMS helper.

> - Use the hardcoded bits per pixel per variant instead of

>   trying to be heuristic about this setting for now.

> ---

>  drivers/gpu/drm/pl111/pl111_display.c | 30 ++++++++++++++++++++++++++++++

>  drivers/gpu/drm/pl111/pl111_drm.h     |  1 +

>  drivers/gpu/drm/pl111/pl111_drv.c     |  6 ++++++

>  3 files changed, 37 insertions(+)

>

> diff --git a/drivers/gpu/drm/pl111/pl111_display.c b/drivers/gpu/drm/pl111/pl111_display.c

> index d75923896609..a1ca9e1ffe15 100644

> --- a/drivers/gpu/drm/pl111/pl111_display.c

> +++ b/drivers/gpu/drm/pl111/pl111_display.c


> +	if (bw > priv->memory_bw) {

> +		DRM_DEBUG("%d x %d @ %d Hz, %d cpp, bw %llu too fast\n",

> +			  mode->hdisplay, mode->vdisplay, mode->clock, cpp, bw);

> +

> +		return MODE_BAD;

> +	}


Oh, hey, on platforms with no memory-bandwidth property, we should make
sure not to reject all modes :)

Patch

diff --git a/drivers/gpu/drm/pl111/pl111_display.c b/drivers/gpu/drm/pl111/pl111_display.c
index d75923896609..a1ca9e1ffe15 100644
--- a/drivers/gpu/drm/pl111/pl111_display.c
+++ b/drivers/gpu/drm/pl111/pl111_display.c
@@ -50,6 +50,35 @@  irqreturn_t pl111_irq(int irq, void *data)
 	return status;
 }
 
+static enum drm_mode_status
+pl111_mode_valid(struct drm_crtc *crtc,
+		 const struct drm_display_mode *mode)
+{
+	struct drm_device *drm = crtc->dev;
+	struct pl111_drm_dev_private *priv = drm->dev_private;
+	u32 cpp = priv->variant->fb_bpp / 8;
+	u64 bw;
+
+	/*
+	 * We use the pixelclock to also account for interlaced modes, the
+	 * resulting bandwidth is in bytes per second.
+	 */
+	bw = mode->clock * 1000; /* In Hz */
+	bw = bw * mode->hdisplay * mode->vdisplay * cpp;
+	bw = div_u64(bw, mode->htotal * mode->vtotal);
+
+	if (bw > priv->memory_bw) {
+		DRM_DEBUG("%d x %d @ %d Hz, %d cpp, bw %llu too fast\n",
+			  mode->hdisplay, mode->vdisplay, mode->clock, cpp, bw);
+
+		return MODE_BAD;
+	}
+	DRM_DEBUG("%d x %d @ %d Hz, %d cpp, bw %llu bytes/s OK\n",
+		  mode->hdisplay, mode->vdisplay, mode->clock, cpp, bw);
+
+	return MODE_OK;
+}
+
 static int pl111_display_check(struct drm_simple_display_pipe *pipe,
 			       struct drm_plane_state *pstate,
 			       struct drm_crtc_state *cstate)
@@ -344,6 +373,7 @@  static int pl111_display_prepare_fb(struct drm_simple_display_pipe *pipe,
 }
 
 static const struct drm_simple_display_pipe_funcs pl111_display_funcs = {
+	.mode_valid = pl111_mode_valid,
 	.check = pl111_display_check,
 	.enable = pl111_display_enable,
 	.disable = pl111_display_disable,
diff --git a/drivers/gpu/drm/pl111/pl111_drm.h b/drivers/gpu/drm/pl111/pl111_drm.h
index 9f2d30b52e7a..7a3d7af1c8cf 100644
--- a/drivers/gpu/drm/pl111/pl111_drm.h
+++ b/drivers/gpu/drm/pl111/pl111_drm.h
@@ -66,6 +66,7 @@  struct pl111_drm_dev_private {
 	struct drm_fbdev_cma *fbdev;
 
 	void *regs;
+	u32 memory_bw;
 	u32 ienb;
 	u32 ctrl;
 	/* The pixel clock (a reference to our clock divider off of CLCDCLK). */
diff --git a/drivers/gpu/drm/pl111/pl111_drv.c b/drivers/gpu/drm/pl111/pl111_drv.c
index f5d5aa464ae2..0077059c897f 100644
--- a/drivers/gpu/drm/pl111/pl111_drv.c
+++ b/drivers/gpu/drm/pl111/pl111_drv.c
@@ -274,6 +274,12 @@  static int pl111_amba_probe(struct amba_device *amba_dev,
 	drm->dev_private = priv;
 	priv->variant = variant;
 
+	if (of_property_read_u32(dev->of_node, "max-memory-bandwidth",
+				 &priv->memory_bw)) {
+		dev_info(dev, "no max memory bandwidth specified, assume unlimited\n");
+		priv->memory_bw = 0;
+	}
+
 	/* The two variants swap this register */
 	if (variant->is_pl110) {
 		priv->ienb = CLCD_PL110_IENB;