[v8] drm/panel: Add a driver for the TPO TPG110

The TPO (Toppoly) TPG110 is a pretty generic display driver
similar in vein to the Ilitek 93xx devices. It is not a panel
per se but a driver used with several low-cost noname panels.

This is used on the Nomadik NHK15 combined with a OSD
OSD057VA01CT display for WVGA 800x480.

The driver is pretty minimalistic right now but can be
extended to handle non-default polarities, gamma correction
etc.

The driver is based on the baked-in code in
drivers/video/fbdev/amba-clcd-nomadik.c which will be
decomissioned once this us upstream.

Cc: Noralf Trønnes <noralf@tronnes.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
ChangeLog v7->v8:
- Lifecycle the backlight properly with devm_of_find_backlight()
- Drop if (backlight) clauses since helper are NULL-tolerant
ChangeLog v6->v7:
- Drop the video mode helpers.
- Do not include <drm/drmP.h> but instead the granular APIs.
- Switch dev_info() and dev_err() for DRM_DEV_INFO()
  and DRM_DEV_ERROR().
- Switch mdelay(1) for usleep_range(1000,2000) so we don't
  spin unecessarily during boot.
- Use DRM_DEV_DEBUG() for information about deasserted reset.
- Make a proper DRM_DEV_ERROR() for illegal resolution settings.
- Simplify the inlined backlight enable/disable code by using
  the existing inline helpers.
- Add a few missing stray \n's
ChangeLog v5->v6:
- Collected Sam's ACK.
ChangeLog v4->v5:
- Assign proper bus_flags.
- This is now the only remaining patch.
ChangeLog v3->v4:
- Tag on the SPI_3WIRE_HIZ flag to the SPI slave mode.
ChangeLog v2->v3:
- Rewrite as an SPI child device.
---
 MAINTAINERS                              |   7 +
 drivers/gpu/drm/panel/Kconfig            |   9 +
 drivers/gpu/drm/panel/Makefile           |   1 +
 drivers/gpu/drm/panel/panel-tpo-tpg110.c | 496 +++++++++++++++++++++++
 4 files changed, 513 insertions(+)
 create mode 100644 drivers/gpu/drm/panel/panel-tpo-tpg110.c

Den 11.01.2019 18.54, skrev Linus Walleij:
> The TPO (Toppoly) TPG110 is a pretty generic display driver
> similar in vein to the Ilitek 93xx devices. It is not a panel
> per se but a driver used with several low-cost noname panels.
> 
> This is used on the Nomadik NHK15 combined with a OSD
> OSD057VA01CT display for WVGA 800x480.
> 
> The driver is pretty minimalistic right now but can be
> extended to handle non-default polarities, gamma correction
> etc.
> 
> The driver is based on the baked-in code in
> drivers/video/fbdev/amba-clcd-nomadik.c which will be
> decomissioned once this us upstream.
> 
> Cc: Noralf Trønnes <noralf@tronnes.org>
> Acked-by: Sam Ravnborg <sam@ravnborg.org>
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> ---

Seems like it could make sense to add a devm_drm_panel_add(), but maybe
for another day.

Acked-by: Noralf Trønnes <noralf@tronnes.org>


> ChangeLog v7->v8:
> - Lifecycle the backlight properly with devm_of_find_backlight()
> - Drop if (backlight) clauses since helper are NULL-tolerant
> ChangeLog v6->v7:
> - Drop the video mode helpers.
> - Do not include <drm/drmP.h> but instead the granular APIs.
> - Switch dev_info() and dev_err() for DRM_DEV_INFO()
>   and DRM_DEV_ERROR().
> - Switch mdelay(1) for usleep_range(1000,2000) so we don't
>   spin unecessarily during boot.
> - Use DRM_DEV_DEBUG() for information about deasserted reset.
> - Make a proper DRM_DEV_ERROR() for illegal resolution settings.
> - Simplify the inlined backlight enable/disable code by using
>   the existing inline helpers.
> - Add a few missing stray \n's
> ChangeLog v5->v6:
> - Collected Sam's ACK.
> ChangeLog v4->v5:
> - Assign proper bus_flags.
> - This is now the only remaining patch.
> ChangeLog v3->v4:
> - Tag on the SPI_3WIRE_HIZ flag to the SPI slave mode.
> ChangeLog v2->v3:
> - Rewrite as an SPI child device.
> ---
>  MAINTAINERS                              |   7 +
>  drivers/gpu/drm/panel/Kconfig            |   9 +
>  drivers/gpu/drm/panel/Makefile           |   1 +
>  drivers/gpu/drm/panel/panel-tpo-tpg110.c | 496 +++++++++++++++++++++++
>  4 files changed, 513 insertions(+)
>  create mode 100644 drivers/gpu/drm/panel/panel-tpo-tpg110.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 32d444476a90..e177473d5417 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -4909,6 +4909,13 @@ DRM DRIVER FOR TDFX VIDEO CARDS
>  S:	Orphan / Obsolete
>  F:	drivers/gpu/drm/tdfx/
>  
> +DRM DRIVER FOR TPO TPG110 PANELS
> +M:	Linus Walleij <linus.walleij@linaro.org>
> +T:	git git://anongit.freedesktop.org/drm/drm-misc
> +S:	Maintained
> +F:	drivers/gpu/drm/panel/panel-tpo-tpg110.c
> +F:	Documentation/devicetree/bindings/display/panel/tpo,tpg110.txt
> +
>  DRM DRIVER FOR USB DISPLAYLINK VIDEO ADAPTERS
>  M:	Dave Airlie <airlied@redhat.com>
>  R:	Sean Paul <sean@poorly.run>
> diff --git a/drivers/gpu/drm/panel/Kconfig b/drivers/gpu/drm/panel/Kconfig
> index 3f3537719beb..a71f44191273 100644
> --- a/drivers/gpu/drm/panel/Kconfig
> +++ b/drivers/gpu/drm/panel/Kconfig
> @@ -204,6 +204,15 @@ config DRM_PANEL_SITRONIX_ST7789V
>  	  Say Y here if you want to enable support for the Sitronix
>  	  ST7789V controller for 240x320 LCD panels
>  
> +config DRM_PANEL_TPO_TPG110
> +	tristate "TPO TPG 800x400 panel"
> +	depends on OF && SPI && GPIOLIB
> +	depends on BACKLIGHT_CLASS_DEVICE
> +	help
> +	  Say Y here if you want to enable support for TPO TPG110
> +	  400CH LTPS TFT LCD Single Chip Digital Driver for up to
> +	  800x400 LCD panels.
> +
>  config DRM_PANEL_TRULY_NT35597_WQXGA
>  	tristate "Truly WQXGA"
>  	depends on OF
> diff --git a/drivers/gpu/drm/panel/Makefile b/drivers/gpu/drm/panel/Makefile
> index 4396658a7996..cd14ca39c6e0 100644
> --- a/drivers/gpu/drm/panel/Makefile
> +++ b/drivers/gpu/drm/panel/Makefile
> @@ -21,4 +21,5 @@ obj-$(CONFIG_DRM_PANEL_SEIKO_43WVF1G) += panel-seiko-43wvf1g.o
>  obj-$(CONFIG_DRM_PANEL_SHARP_LQ101R1SX01) += panel-sharp-lq101r1sx01.o
>  obj-$(CONFIG_DRM_PANEL_SHARP_LS043T1LE01) += panel-sharp-ls043t1le01.o
>  obj-$(CONFIG_DRM_PANEL_SITRONIX_ST7789V) += panel-sitronix-st7789v.o
> +obj-$(CONFIG_DRM_PANEL_TPO_TPG110) += panel-tpo-tpg110.o
>  obj-$(CONFIG_DRM_PANEL_TRULY_NT35597_WQXGA) += panel-truly-nt35597.o
> diff --git a/drivers/gpu/drm/panel/panel-tpo-tpg110.c b/drivers/gpu/drm/panel/panel-tpo-tpg110.c
> new file mode 100644
> index 000000000000..5a9f8f4d5d24
> --- /dev/null
> +++ b/drivers/gpu/drm/panel/panel-tpo-tpg110.c
> @@ -0,0 +1,496 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Panel driver for the TPO TPG110 400CH LTPS TFT LCD Single Chip
> + * Digital Driver.
> + *
> + * This chip drives a TFT LCD, so it does not know what kind of
> + * display is actually connected to it, so the width and height of that
> + * display needs to be supplied from the machine configuration.
> + *
> + * Author:
> + * Linus Walleij <linus.walleij@linaro.org>
> + */
> +#include <drm/drm_modes.h>
> +#include <drm/drm_panel.h>
> +#include <drm/drm_print.h>
> +
> +#include <linux/backlight.h>
> +#include <linux/bitops.h>
> +#include <linux/delay.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/init.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/spi/spi.h>
> +
> +#define TPG110_TEST			0x00
> +#define TPG110_CHIPID			0x01
> +#define TPG110_CTRL1			0x02
> +#define TPG110_RES_MASK			GENMASK(2, 0)
> +#define TPG110_RES_800X480		0x07
> +#define TPG110_RES_640X480		0x06
> +#define TPG110_RES_480X272		0x05
> +#define TPG110_RES_480X640		0x04
> +#define TPG110_RES_480X272_D		0x01 /* Dual scan: outputs 800x480 */
> +#define TPG110_RES_400X240_D		0x00 /* Dual scan: outputs 800x480 */
> +#define TPG110_CTRL2			0x03
> +#define TPG110_CTRL2_PM			BIT(0)
> +#define TPG110_CTRL2_RES_PM_CTRL	BIT(7)
> +
> +/**
> + * struct tpg110_panel_mode - lookup struct for the supported modes
> + */
> +struct tpg110_panel_mode {
> +	/**
> +	 * @name: the name of this panel
> +	 */
> +	const char *name;
> +	/**
> +	 * @magic: the magic value from the detection register
> +	 */
> +	u32 magic;
> +	/**
> +	 * @mode: the DRM display mode for this panel
> +	 */
> +	struct drm_display_mode mode;
> +	/**
> +	 * @bus_flags: the DRM bus flags for this panel e.g. inverted clock
> +	 */
> +	u32 bus_flags;
> +};
> +
> +/**
> + * struct tpg110 - state container for the TPG110 panel
> + */
> +struct tpg110 {
> +	/**
> +	 * @dev: the container device
> +	 */
> +	struct device *dev;
> +	/**
> +	 * @spi: the corresponding SPI device
> +	 */
> +	struct spi_device *spi;
> +	/**
> +	 * @panel: the DRM panel instance for this device
> +	 */
> +	struct drm_panel panel;
> +	/**
> +	 * @backlight: backlight for this panel
> +	 */
> +	struct backlight_device *backlight;
> +	/**
> +	 * @panel_type: the panel mode as detected
> +	 */
> +	const struct tpg110_panel_mode *panel_mode;
> +	/**
> +	 * @width: the width of this panel in mm
> +	 */
> +	u32 width;
> +	/**
> +	 * @height: the height of this panel in mm
> +	 */
> +	u32 height;
> +	/**
> +	 * @grestb: reset GPIO line
> +	 */
> +	struct gpio_desc *grestb;
> +};
> +
> +/*
> + * TPG110 modes, these are the simple modes, the dualscan modes that
> + * take 400x240 or 480x272 in and display as 800x480 are not listed.
> + */
> +static const struct tpg110_panel_mode tpg110_modes[] = {
> +	{
> +		.name = "800x480 RGB",
> +		.magic = TPG110_RES_800X480,
> +		.mode = {
> +			.clock = 33200,
> +			.hdisplay = 800,
> +			.hsync_start = 800 + 40,
> +			.hsync_end = 800 + 40 + 1,
> +			.htotal = 800 + 40 + 1 + 216,
> +			.vdisplay = 480,
> +			.vsync_start = 480 + 10,
> +			.vsync_end = 480 + 10 + 1,
> +			.vtotal = 480 + 10 + 1 + 35,
> +			.vrefresh = 60,
> +		},
> +		.bus_flags = DRM_BUS_FLAG_PIXDATA_POSEDGE,
> +	},
> +	{
> +		.name = "640x480 RGB",
> +		.magic = TPG110_RES_640X480,
> +		.mode = {
> +			.clock = 25200,
> +			.hdisplay = 640,
> +			.hsync_start = 640 + 24,
> +			.hsync_end = 640 + 24 + 1,
> +			.htotal = 640 + 24 + 1 + 136,
> +			.vdisplay = 480,
> +			.vsync_start = 480 + 18,
> +			.vsync_end = 480 + 18 + 1,
> +			.vtotal = 480 + 18 + 1 + 27,
> +			.vrefresh = 60,
> +		},
> +		.bus_flags = DRM_BUS_FLAG_PIXDATA_POSEDGE,
> +	},
> +	{
> +		.name = "480x272 RGB",
> +		.magic = TPG110_RES_480X272,
> +		.mode = {
> +			.clock = 9000,
> +			.hdisplay = 480,
> +			.hsync_start = 480 + 2,
> +			.hsync_end = 480 + 2 + 1,
> +			.htotal = 480 + 2 + 1 + 43,
> +			.vdisplay = 272,
> +			.vsync_start = 272 + 2,
> +			.vsync_end = 272 + 2 + 1,
> +			.vtotal = 272 + 2 + 1 + 12,
> +			.vrefresh = 60,
> +		},
> +		.bus_flags = DRM_BUS_FLAG_PIXDATA_POSEDGE,
> +	},
> +	{
> +		.name = "480x640 RGB",
> +		.magic = TPG110_RES_480X640,
> +		.mode = {
> +			.clock = 20500,
> +			.hdisplay = 480,
> +			.hsync_start = 480 + 2,
> +			.hsync_end = 480 + 2 + 1,
> +			.htotal = 480 + 2 + 1 + 43,
> +			.vdisplay = 640,
> +			.vsync_start = 640 + 4,
> +			.vsync_end = 640 + 4 + 1,
> +			.vtotal = 640 + 4 + 1 + 8,
> +			.vrefresh = 60,
> +		},
> +		.bus_flags = DRM_BUS_FLAG_PIXDATA_POSEDGE,
> +	},
> +	{
> +		.name = "400x240 RGB",
> +		.magic = TPG110_RES_400X240_D,
> +		.mode = {
> +			.clock = 8300,
> +			.hdisplay = 400,
> +			.hsync_start = 400 + 20,
> +			.hsync_end = 400 + 20 + 1,
> +			.htotal = 400 + 20 + 1 + 108,
> +			.vdisplay = 240,
> +			.vsync_start = 240 + 2,
> +			.vsync_end = 240 + 2 + 1,
> +			.vtotal = 240 + 2 + 1 + 20,
> +			.vrefresh = 60,
> +		},
> +		.bus_flags = DRM_BUS_FLAG_PIXDATA_POSEDGE,
> +	},
> +};
> +
> +static inline struct tpg110 *
> +to_tpg110(struct drm_panel *panel)
> +{
> +	return container_of(panel, struct tpg110, panel);
> +}
> +
> +static u8 tpg110_readwrite_reg(struct tpg110 *tpg, bool write,
> +			       u8 address, u8 outval)
> +{
> +	struct spi_message m;
> +	struct spi_transfer t[2];
> +	u8 buf[2];
> +	int ret;
> +
> +	spi_message_init(&m);
> +	memset(t, 0, sizeof(t));
> +
> +	if (write) {
> +		/*
> +		 * Clear address bit 0, 1 when writing, just to be sure
> +		 * The actual bit indicating a write here is bit 1, bit
> +		 * 0 is just surplus to pad it up to 8 bits.
> +		 */
> +		buf[0] = address << 2;
> +		buf[0] &= ~0x03;
> +		buf[1] = outval;
> +
> +		t[0].bits_per_word = 8;
> +		t[0].tx_buf = &buf[0];
> +		t[0].len = 1;
> +
> +		t[1].tx_buf = &buf[1];
> +		t[1].len = 1;
> +		t[1].bits_per_word = 8;
> +	} else {
> +		/* Set address bit 0 to 1 to read */
> +		buf[0] = address << 1;
> +		buf[0] |= 0x01;
> +
> +		/*
> +		 * The last bit/clock is Hi-Z turnaround cycle, so we need
> +		 * to send only 7 bits here. The 8th bit is the high impedance
> +		 * turn-around cycle.
> +		 */
> +		t[0].bits_per_word = 7;
> +		t[0].tx_buf = &buf[0];
> +		t[0].len = 1;
> +
> +		t[1].rx_buf = &buf[1];
> +		t[1].len = 1;
> +		t[1].bits_per_word = 8;
> +	}
> +
> +	spi_message_add_tail(&t[0], &m);
> +	spi_message_add_tail(&t[1], &m);
> +	ret = spi_sync(tpg->spi, &m);
> +	if (ret) {
> +		DRM_DEV_ERROR(tpg->dev, "SPI message error %d\n", ret);
> +		return ret;
> +	}
> +	if (write)
> +		return 0;
> +	/* Read */
> +	return buf[1];
> +}
> +
> +static u8 tpg110_read_reg(struct tpg110 *tpg, u8 address)
> +{
> +	return tpg110_readwrite_reg(tpg, false, address, 0);
> +}
> +
> +static void tpg110_write_reg(struct tpg110 *tpg, u8 address, u8 outval)
> +{
> +	tpg110_readwrite_reg(tpg, true, address, outval);
> +}
> +
> +static int tpg110_startup(struct tpg110 *tpg)
> +{
> +	u8 val;
> +	int i;
> +
> +	/* De-assert the reset signal */
> +	gpiod_set_value_cansleep(tpg->grestb, 0);
> +	usleep_range(1000, 2000);
> +	DRM_DEV_DEBUG(tpg->dev, "de-asserted GRESTB\n");
> +
> +	/* Test display communication */
> +	tpg110_write_reg(tpg, TPG110_TEST, 0x55);
> +	val = tpg110_read_reg(tpg, TPG110_TEST);
> +	if (val != 0x55) {
> +		DRM_DEV_ERROR(tpg->dev, "failed communication test\n");
> +		return -ENODEV;
> +	}
> +
> +	val = tpg110_read_reg(tpg, TPG110_CHIPID);
> +	DRM_DEV_INFO(tpg->dev, "TPG110 chip ID: %d version: %d\n",
> +		 val >> 4, val & 0x0f);
> +
> +	/* Show display resolution */
> +	val = tpg110_read_reg(tpg, TPG110_CTRL1);
> +	val &= TPG110_RES_MASK;
> +	switch (val) {
> +	case TPG110_RES_400X240_D:
> +		DRM_DEV_INFO(tpg->dev,
> +			 "IN 400x240 RGB -> OUT 800x480 RGB (dual scan)\n");
> +		break;
> +	case TPG110_RES_480X272_D:
> +		DRM_DEV_INFO(tpg->dev,
> +			 "IN 480x272 RGB -> OUT 800x480 RGB (dual scan)\n");
> +		break;
> +	case TPG110_RES_480X640:
> +		DRM_DEV_INFO(tpg->dev, "480x640 RGB\n");
> +		break;
> +	case TPG110_RES_480X272:
> +		DRM_DEV_INFO(tpg->dev, "480x272 RGB\n");
> +		break;
> +	case TPG110_RES_640X480:
> +		DRM_DEV_INFO(tpg->dev, "640x480 RGB\n");
> +		break;
> +	case TPG110_RES_800X480:
> +		DRM_DEV_INFO(tpg->dev, "800x480 RGB\n");
> +		break;
> +	default:
> +		DRM_DEV_ERROR(tpg->dev, "ILLEGAL RESOLUTION 0x%02x\n", val);
> +		break;
> +	}
> +
> +	/* From the producer side, this is the same resolution */
> +	if (val == TPG110_RES_480X272_D)
> +		val = TPG110_RES_480X272;
> +
> +	for (i = 0; i < ARRAY_SIZE(tpg110_modes); i++) {
> +		const struct tpg110_panel_mode *pm;
> +
> +		pm = &tpg110_modes[i];
> +		if (pm->magic == val) {
> +			tpg->panel_mode = pm;
> +			break;
> +		}
> +	}
> +	if (i == ARRAY_SIZE(tpg110_modes)) {
> +		DRM_DEV_ERROR(tpg->dev, "unsupported mode (%02x) detected\n",
> +			val);
> +		return -ENODEV;
> +	}
> +
> +	val = tpg110_read_reg(tpg, TPG110_CTRL2);
> +	DRM_DEV_INFO(tpg->dev, "resolution and standby is controlled by %s\n",
> +		 (val & TPG110_CTRL2_RES_PM_CTRL) ? "software" : "hardware");
> +	/* Take control over resolution and standby */
> +	val |= TPG110_CTRL2_RES_PM_CTRL;
> +	tpg110_write_reg(tpg, TPG110_CTRL2, val);
> +
> +	return 0;
> +}
> +
> +static int tpg110_disable(struct drm_panel *panel)
> +{
> +	struct tpg110 *tpg = to_tpg110(panel);
> +	u8 val;
> +
> +	/* Put chip into standby */
> +	val = tpg110_read_reg(tpg, TPG110_CTRL2_PM);
> +	val &= ~TPG110_CTRL2_PM;
> +	tpg110_write_reg(tpg, TPG110_CTRL2_PM, val);
> +
> +	backlight_disable(tpg->backlight);
> +
> +	return 0;
> +}
> +
> +static int tpg110_enable(struct drm_panel *panel)
> +{
> +	struct tpg110 *tpg = to_tpg110(panel);
> +	u8 val;
> +
> +	backlight_enable(tpg->backlight);
> +
> +	/* Take chip out of standby */
> +	val = tpg110_read_reg(tpg, TPG110_CTRL2_PM);
> +	val |= TPG110_CTRL2_PM;
> +	tpg110_write_reg(tpg, TPG110_CTRL2_PM, val);
> +
> +	return 0;
> +}
> +
> +/**
> + * tpg110_get_modes() - return the appropriate mode
> + * @panel: the panel to get the mode for
> + *
> + * This currently does not present a forest of modes, instead it
> + * presents the mode that is configured for the system under use,
> + * and which is detected by reading the registers of the display.
> + */
> +static int tpg110_get_modes(struct drm_panel *panel)
> +{
> +	struct drm_connector *connector = panel->connector;
> +	struct tpg110 *tpg = to_tpg110(panel);
> +	struct drm_display_mode *mode;
> +
> +	strncpy(connector->display_info.name, tpg->panel_mode->name,
> +		DRM_DISPLAY_INFO_LEN);
> +	connector->display_info.width_mm = tpg->width;
> +	connector->display_info.height_mm = tpg->height;
> +	connector->display_info.bus_flags = tpg->panel_mode->bus_flags;
> +
> +	mode = drm_mode_duplicate(panel->drm, &tpg->panel_mode->mode);
> +	drm_mode_set_name(mode);
> +	mode->type = DRM_MODE_TYPE_DRIVER | DRM_MODE_TYPE_PREFERRED;
> +
> +	mode->width_mm = tpg->width;
> +	mode->height_mm = tpg->height;
> +
> +	drm_mode_probed_add(connector, mode);
> +
> +	return 1;
> +}
> +
> +static const struct drm_panel_funcs tpg110_drm_funcs = {
> +	.disable = tpg110_disable,
> +	.enable = tpg110_enable,
> +	.get_modes = tpg110_get_modes,
> +};
> +
> +static int tpg110_probe(struct spi_device *spi)
> +{
> +	struct device *dev = &spi->dev;
> +	struct device_node *np = dev->of_node;
> +	struct tpg110 *tpg;
> +	int ret;
> +
> +	tpg = devm_kzalloc(dev, sizeof(*tpg), GFP_KERNEL);
> +	if (!tpg)
> +		return -ENOMEM;
> +	tpg->dev = dev;
> +
> +	/* We get the physical display dimensions from the DT */
> +	ret = of_property_read_u32(np, "width-mm", &tpg->width);
> +	if (ret)
> +		DRM_DEV_ERROR(dev, "no panel width specified\n");
> +	ret = of_property_read_u32(np, "height-mm", &tpg->height);
> +	if (ret)
> +		DRM_DEV_ERROR(dev, "no panel height specified\n");
> +
> +	/* Look for some optional backlight */
> +	tpg->backlight = devm_of_find_backlight(dev);
> +	if (IS_ERR(tpg->backlight))
> +		return PTR_ERR(tpg->backlight);
> +
> +	/* This asserts the GRESTB signal, putting the display into reset */
> +	tpg->grestb = devm_gpiod_get(dev, "grestb", GPIOD_OUT_HIGH);
> +	if (IS_ERR(tpg->grestb)) {
> +		DRM_DEV_ERROR(dev, "no GRESTB GPIO\n");
> +		return -ENODEV;
> +	}
> +
> +	spi->bits_per_word = 8;
> +	spi->mode |= SPI_3WIRE_HIZ;
> +	ret = spi_setup(spi);
> +	if (ret < 0) {
> +		DRM_DEV_ERROR(dev, "spi setup failed.\n");
> +		return ret;
> +	}
> +	tpg->spi = spi;
> +
> +	ret = tpg110_startup(tpg);
> +	if (ret)
> +		return ret;
> +
> +	drm_panel_init(&tpg->panel);
> +	tpg->panel.dev = dev;
> +	tpg->panel.funcs = &tpg110_drm_funcs;
> +	spi_set_drvdata(spi, tpg);
> +
> +	return drm_panel_add(&tpg->panel);
> +}
> +
> +static int tpg110_remove(struct spi_device *spi)
> +{
> +	struct tpg110 *tpg = spi_get_drvdata(spi);
> +
> +	drm_panel_remove(&tpg->panel);
> +	return 0;
> +}
> +
> +static const struct of_device_id tpg110_match[] = {
> +	{ .compatible = "tpo,tpg110", },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, tpg110_match);
> +
> +static struct spi_driver tpg110_driver = {
> +	.probe		= tpg110_probe,
> +	.remove		= tpg110_remove,
> +	.driver		= {
> +		.name	= "tpo-tpg110-panel",
> +		.of_match_table = tpg110_match,
> +	},
> +};
> +module_spi_driver(tpg110_driver);
> +
> +MODULE_AUTHOR("Linus Walleij <linus.walleij@linaro.org>");
> +MODULE_DESCRIPTION("TPO TPG110 panel driver");
> +MODULE_LICENSE("GPL v2");
>

On Fri, Jan 11, 2019 at 11:24 PM Linus Walleij <linus.walleij@linaro.org> wrote:
>
> The TPO (Toppoly) TPG110 is a pretty generic display driver
> similar in vein to the Ilitek 93xx devices. It is not a panel
> per se but a driver used with several low-cost noname panels.
>
> This is used on the Nomadik NHK15 combined with a OSD
> OSD057VA01CT display for WVGA 800x480.
>
> The driver is pretty minimalistic right now but can be
> extended to handle non-default polarities, gamma correction
> etc.
>
> The driver is based on the baked-in code in
> drivers/video/fbdev/amba-clcd-nomadik.c which will be
> decomissioned once this us upstream.
>
> Cc: Noralf Trønnes <noralf@tronnes.org>
> Acked-by: Sam Ravnborg <sam@ravnborg.org>
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> ---
> ChangeLog v7->v8:
> - Lifecycle the backlight properly with devm_of_find_backlight()
> - Drop if (backlight) clauses since helper are NULL-tolerant
> ChangeLog v6->v7:
> - Drop the video mode helpers.
> - Do not include <drm/drmP.h> but instead the granular APIs.
> - Switch dev_info() and dev_err() for DRM_DEV_INFO()
>   and DRM_DEV_ERROR().
> - Switch mdelay(1) for usleep_range(1000,2000) so we don't
>   spin unecessarily during boot.
> - Use DRM_DEV_DEBUG() for information about deasserted reset.
> - Make a proper DRM_DEV_ERROR() for illegal resolution settings.
> - Simplify the inlined backlight enable/disable code by using
>   the existing inline helpers.
> - Add a few missing stray \n's
> ChangeLog v5->v6:
> - Collected Sam's ACK.
> ChangeLog v4->v5:
> - Assign proper bus_flags.
> - This is now the only remaining patch.
> ChangeLog v3->v4:
> - Tag on the SPI_3WIRE_HIZ flag to the SPI slave mode.
> ChangeLog v2->v3:
> - Rewrite as an SPI child device.
> ---
>  MAINTAINERS                              |   7 +
>  drivers/gpu/drm/panel/Kconfig            |   9 +
>  drivers/gpu/drm/panel/Makefile           |   1 +
>  drivers/gpu/drm/panel/panel-tpo-tpg110.c | 496 +++++++++++++++++++++++
>  4 files changed, 513 insertions(+)
>  create mode 100644 drivers/gpu/drm/panel/panel-tpo-tpg110.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 32d444476a90..e177473d5417 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -4909,6 +4909,13 @@ DRM DRIVER FOR TDFX VIDEO CARDS
>  S:     Orphan / Obsolete
>  F:     drivers/gpu/drm/tdfx/
>
> +DRM DRIVER FOR TPO TPG110 PANELS
> +M:     Linus Walleij <linus.walleij@linaro.org>
> +T:     git git://anongit.freedesktop.org/drm/drm-misc
> +S:     Maintained
> +F:     drivers/gpu/drm/panel/panel-tpo-tpg110.c
> +F:     Documentation/devicetree/bindings/display/panel/tpo,tpg110.txt

Except my query about this change in v6, all look fine on this driver.

Acked-by: Jagan Teki <jagan@amarulasolutions.com>