Re: [RFC PATCH] drm/dsi-mipi: Fix byte order of DCS set/get brightness

From: Sam Ravnborg
Date: Fri Jan 13 2023 - 11:38:57 EST

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In reply to: Richard Acayan: "Re: [RFC PATCH] drm/dsi-mipi: Fix byte order of DCS set/get brightness"
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Hi Richard/Daniel.

On Thu, Jan 12, 2023 at 11:18:48PM -0500, Richard Acayan wrote:
> From: Daniel Mentz <danielmentz@xxxxxxxxxx>
>
> The MIPI DCS specification demands that brightness values are sent in
> big endian byte order. It also states that one parameter (i.e. one byte)
> shall be sent/received for 8 bit wide values, and two parameters shall
> be used for values that are between 9 and 16 bits wide.
It is only a few week ago someone write they needed a byteswap to use
the kernel provided mipi_dsi_dcs_set_display_brightness(). I did not
realize then that this is because it is buggy.

Some comments on the patch:
- It would be nice to split it up so first patch fixes that the
parameters are in big-endian. This would go for both set and get.

- Second patch could then introduce the possibility to a driver to
use a variant that matches the display.
I would suggest to go for two functions:
mipi_dsi_dcs_set_display_brightness()
mipi_dsi_dcs_set_display_brightness_two()
So it is obvious when you go for the two byte version without adding a
bool parameter.
If the implementation is done using a helper or two independent
functions are up to you.

The patch split would be nice, but at least we should have two functions
and not a bool parameter.
Both patches should have the same Fixes tag.

Sam

>
> Fixes: 1a9d759331b8 ("drm/dsi: Implement DCS set/get display brightness")
> Signed-off-by: Daniel Mentz <danielmentz@xxxxxxxxxx>
> Change-Id: I24306e21ec6a5ff48ea121d977419a81d5b44152
> Link: https://android.googlesource.com/kernel/msm/+/754affd62d0ee268c686c53169b1dbb7deac8550
> [richard: fix 16-bit brightness_get; change brightness call by all panels on the -next tree]
> Signed-off-by: Richard Acayan <mailingradian@xxxxxxxxx>
> ---
> drivers/gpu/drm/drm_mipi_dsi.c | 44 ++++++++++++++++---
> .../drm/panel/panel-asus-z00t-tm5p5-n35596.c | 4 +-
> .../gpu/drm/panel/panel-boe-bf060y8m-aj0.c | 4 +-
> drivers/gpu/drm/panel/panel-ebbg-ft8719.c | 2 +-
> drivers/gpu/drm/panel/panel-jdi-fhd-r63452.c | 2 +-
> .../gpu/drm/panel/panel-jdi-lt070me05000.c | 4 +-
> drivers/gpu/drm/panel/panel-raydium-rm67191.c | 4 +-
> .../gpu/drm/panel/panel-samsung-s6e63j0x03.c | 2 +-
> drivers/gpu/drm/panel/panel-samsung-sofef00.c | 4 +-
> .../panel/panel-sony-tulip-truly-nt35521.c | 4 +-
> include/drm/drm_mipi_dsi.h | 4 +-
> 11 files changed, 55 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
> index 497ef4b6a90a..1e6dbf986d97 100644
> --- a/drivers/gpu/drm/drm_mipi_dsi.c
> +++ b/drivers/gpu/drm/drm_mipi_dsi.c
> @@ -1180,17 +1180,33 @@ EXPORT_SYMBOL(mipi_dsi_dcs_set_tear_scanline);
> * display
> * @dsi: DSI peripheral device
> * @brightness: brightness value
> + * @num_params: Number of parameters (bytes) to encode brightness value in. The
> + * MIPI specification states that one parameter shall be sent for
> + * devices that support 8-bit brightness levels. For devices that
> + * support brightness levels wider than 8-bit, two parameters
> + * shall be sent.
> *
> * Return: 0 on success or a negative error code on failure.
> */
> int mipi_dsi_dcs_set_display_brightness(struct mipi_dsi_device *dsi,
> - u16 brightness)
> + u16 brightness, size_t num_params)
> {
> - u8 payload[2] = { brightness & 0xff, brightness >> 8 };
> + u8 payload[2];
> ssize_t err;
>
> + switch (num_params) {
> + case 1:
> + payload[0] = brightness & 0xff;
> + break;
> + case 2:
> + payload[0] = brightness >> 8;
> + payload[1] = brightness & 0xff;
> + break;
> + default:
> + return -EINVAL;
> + }
> err = mipi_dsi_dcs_write(dsi, MIPI_DCS_SET_DISPLAY_BRIGHTNESS,
> - payload, sizeof(payload));
> + payload, num_params);
> if (err < 0)
> return err;
>
> @@ -1203,16 +1219,25 @@ EXPORT_SYMBOL(mipi_dsi_dcs_set_display_brightness);
> * of the display
> * @dsi: DSI peripheral device
> * @brightness: brightness value
> + * @num_params: Number of parameters (i.e. bytes) the brightness value is
> + * encoded in. The MIPI specification states that one parameter
> + * shall be returned from devices that support 8-bit brightness
> + * levels. Devices that support brightness levels wider than
> + * 8-bit return two parameters (i.e. bytes).
> *
> * Return: 0 on success or a negative error code on failure.
> */
> int mipi_dsi_dcs_get_display_brightness(struct mipi_dsi_device *dsi,
> - u16 *brightness)
> + u16 *brightness, size_t num_params)
> {
> + u8 payload[2];
> ssize_t err;
>
> + if (!(num_params == 1 || num_params == 2))
> + return -EINVAL;
> +
> err = mipi_dsi_dcs_read(dsi, MIPI_DCS_GET_DISPLAY_BRIGHTNESS,
> - brightness, sizeof(*brightness));
> + payload, num_params);
> if (err <= 0) {
> if (err == 0)
> err = -ENODATA;
> @@ -1220,6 +1245,15 @@ int mipi_dsi_dcs_get_display_brightness(struct mipi_dsi_device *dsi,
> return err;
> }
>
> + switch (num_params) {
> + case 1:
> + *brightness = payload[0];
> + break;
> + case 2:
> + *brightness = (payload[0] << 8) | payload[1];
> + break;
> + }
> +
> return 0;
> }
> EXPORT_SYMBOL(mipi_dsi_dcs_get_display_brightness);
> diff --git a/drivers/gpu/drm/panel/panel-asus-z00t-tm5p5-n35596.c b/drivers/gpu/drm/panel/panel-asus-z00t-tm5p5-n35596.c
> index b3235781e6ba..9f849c68d57c 100644
> --- a/drivers/gpu/drm/panel/panel-asus-z00t-tm5p5-n35596.c
> +++ b/drivers/gpu/drm/panel/panel-asus-z00t-tm5p5-n35596.c
> @@ -220,7 +220,7 @@ static int tm5p5_nt35596_bl_update_status(struct backlight_device *bl)
>
> dsi->mode_flags &= ~MIPI_DSI_MODE_LPM;
>
> - ret = mipi_dsi_dcs_set_display_brightness(dsi, brightness);
> + ret = mipi_dsi_dcs_set_display_brightness(dsi, brightness, 1);
> if (ret < 0)
> return ret;
>
> @@ -237,7 +237,7 @@ static int tm5p5_nt35596_bl_get_brightness(struct backlight_device *bl)
>
> dsi->mode_flags &= ~MIPI_DSI_MODE_LPM;
>
> - ret = mipi_dsi_dcs_get_display_brightness(dsi, &brightness);
> + ret = mipi_dsi_dcs_get_display_brightness(dsi, &brightness, 1);
> if (ret < 0)
> return ret;
>
> diff --git a/drivers/gpu/drm/panel/panel-boe-bf060y8m-aj0.c b/drivers/gpu/drm/panel/panel-boe-bf060y8m-aj0.c
> index ad58840eda41..5a0366366055 100644
> --- a/drivers/gpu/drm/panel/panel-boe-bf060y8m-aj0.c
> +++ b/drivers/gpu/drm/panel/panel-boe-bf060y8m-aj0.c
> @@ -253,7 +253,7 @@ static int boe_bf060y8m_aj0_bl_update_status(struct backlight_device *bl)
> u16 brightness = backlight_get_brightness(bl);
> int ret;
>
> - ret = mipi_dsi_dcs_set_display_brightness(dsi, brightness);
> + ret = mipi_dsi_dcs_set_display_brightness(dsi, brightness, 1);
> if (ret < 0)
> return ret;
>
> @@ -266,7 +266,7 @@ static int boe_bf060y8m_aj0_bl_get_brightness(struct backlight_device *bl)
> u16 brightness;
> int ret;
>
> - ret = mipi_dsi_dcs_get_display_brightness(dsi, &brightness);
> + ret = mipi_dsi_dcs_get_display_brightness(dsi, &brightness, 1);
> if (ret < 0)
> return ret;
>
> diff --git a/drivers/gpu/drm/panel/panel-ebbg-ft8719.c b/drivers/gpu/drm/panel/panel-ebbg-ft8719.c
> index e85d63a176d0..0666e0390c7c 100644
> --- a/drivers/gpu/drm/panel/panel-ebbg-ft8719.c
> +++ b/drivers/gpu/drm/panel/panel-ebbg-ft8719.c
> @@ -62,7 +62,7 @@ static int ebbg_ft8719_on(struct ebbg_ft8719 *ctx)
>
> dsi->mode_flags |= MIPI_DSI_MODE_LPM;
>
> - ret = mipi_dsi_dcs_set_display_brightness(dsi, 0x00ff);
> + ret = mipi_dsi_dcs_set_display_brightness(dsi, 0x00ff, 1);
> if (ret < 0) {
> dev_err(dev, "Failed to set display brightness: %d\n", ret);
> return ret;
> diff --git a/drivers/gpu/drm/panel/panel-jdi-fhd-r63452.c b/drivers/gpu/drm/panel/panel-jdi-fhd-r63452.c
> index d8765b2294fb..47ebf7b7da4a 100644
> --- a/drivers/gpu/drm/panel/panel-jdi-fhd-r63452.c
> +++ b/drivers/gpu/drm/panel/panel-jdi-fhd-r63452.c
> @@ -102,7 +102,7 @@ static int jdi_fhd_r63452_on(struct jdi_fhd_r63452 *ctx)
> return ret;
> }
>
> - ret = mipi_dsi_dcs_set_display_brightness(dsi, 0x00ff);
> + ret = mipi_dsi_dcs_set_display_brightness(dsi, 0x00ff, 1);
> if (ret < 0) {
> dev_err(dev, "Failed to set display brightness: %d\n", ret);
> return ret;
> diff --git a/drivers/gpu/drm/panel/panel-jdi-lt070me05000.c b/drivers/gpu/drm/panel/panel-jdi-lt070me05000.c
> index 8f4f137a2af6..7d2f147a2504 100644
> --- a/drivers/gpu/drm/panel/panel-jdi-lt070me05000.c
> +++ b/drivers/gpu/drm/panel/panel-jdi-lt070me05000.c
> @@ -332,7 +332,7 @@ static int dsi_dcs_bl_get_brightness(struct backlight_device *bl)
>
> dsi->mode_flags &= ~MIPI_DSI_MODE_LPM;
>
> - ret = mipi_dsi_dcs_get_display_brightness(dsi, &brightness);
> + ret = mipi_dsi_dcs_get_display_brightness(dsi, &brightness, 1);
> if (ret < 0)
> return ret;
>
> @@ -348,7 +348,7 @@ static int dsi_dcs_bl_update_status(struct backlight_device *bl)
>
> dsi->mode_flags &= ~MIPI_DSI_MODE_LPM;
>
> - ret = mipi_dsi_dcs_set_display_brightness(dsi, bl->props.brightness);
> + ret = mipi_dsi_dcs_set_display_brightness(dsi, bl->props.brightness, 1);
> if (ret < 0)
> return ret;
>
> diff --git a/drivers/gpu/drm/panel/panel-raydium-rm67191.c b/drivers/gpu/drm/panel/panel-raydium-rm67191.c
> index dbb1ed4efbed..00f6bd163af2 100644
> --- a/drivers/gpu/drm/panel/panel-raydium-rm67191.c
> +++ b/drivers/gpu/drm/panel/panel-raydium-rm67191.c
> @@ -473,7 +473,7 @@ static int rad_bl_get_brightness(struct backlight_device *bl)
>
> dsi->mode_flags &= ~MIPI_DSI_MODE_LPM;
>
> - ret = mipi_dsi_dcs_get_display_brightness(dsi, &brightness);
> + ret = mipi_dsi_dcs_get_display_brightness(dsi, &brightness, 1);
> if (ret < 0)
> return ret;
>
> @@ -493,7 +493,7 @@ static int rad_bl_update_status(struct backlight_device *bl)
>
> dsi->mode_flags &= ~MIPI_DSI_MODE_LPM;
>
> - ret = mipi_dsi_dcs_set_display_brightness(dsi, bl->props.brightness);
> + ret = mipi_dsi_dcs_set_display_brightness(dsi, bl->props.brightness, 1);
> if (ret < 0)
> return ret;
>
> diff --git a/drivers/gpu/drm/panel/panel-samsung-s6e63j0x03.c b/drivers/gpu/drm/panel/panel-samsung-s6e63j0x03.c
> index e06fd35de814..f5e235db7ad2 100644
> --- a/drivers/gpu/drm/panel/panel-samsung-s6e63j0x03.c
> +++ b/drivers/gpu/drm/panel/panel-samsung-s6e63j0x03.c
> @@ -365,7 +365,7 @@ static int s6e63j0x03_enable(struct drm_panel *panel)
> return ret;
>
> /* set default white brightness */
> - ret = mipi_dsi_dcs_set_display_brightness(dsi, 0x00ff);
> + ret = mipi_dsi_dcs_set_display_brightness(dsi, 0x00ff, 1);
> if (ret < 0)
> return ret;
>
> diff --git a/drivers/gpu/drm/panel/panel-samsung-sofef00.c b/drivers/gpu/drm/panel/panel-samsung-sofef00.c
> index 1a0d24595faa..b481195c9b8f 100644
> --- a/drivers/gpu/drm/panel/panel-samsung-sofef00.c
> +++ b/drivers/gpu/drm/panel/panel-samsung-sofef00.c
> @@ -224,10 +224,8 @@ static int sofef00_panel_bl_update_status(struct backlight_device *bl)
> u16 brightness;
>
> brightness = (u16)backlight_get_brightness(bl);
> - // This panel needs the high and low bytes swapped for the brightness value
> - brightness = __swab16(brightness);
>
> - err = mipi_dsi_dcs_set_display_brightness(dsi, brightness);
> + err = mipi_dsi_dcs_set_display_brightness(dsi, brightness, 2);
> if (err < 0)
> return err;
>
> diff --git a/drivers/gpu/drm/panel/panel-sony-tulip-truly-nt35521.c b/drivers/gpu/drm/panel/panel-sony-tulip-truly-nt35521.c
> index fa9be3c299c0..dbf179fdda88 100644
> --- a/drivers/gpu/drm/panel/panel-sony-tulip-truly-nt35521.c
> +++ b/drivers/gpu/drm/panel/panel-sony-tulip-truly-nt35521.c
> @@ -420,7 +420,7 @@ static int truly_nt35521_bl_update_status(struct backlight_device *bl)
> u16 brightness = backlight_get_brightness(bl);
> int ret;
>
> - ret = mipi_dsi_dcs_set_display_brightness(dsi, brightness);
> + ret = mipi_dsi_dcs_set_display_brightness(dsi, brightness, 1);
> if (ret < 0)
> return ret;
>
> @@ -433,7 +433,7 @@ static int truly_nt35521_bl_get_brightness(struct backlight_device *bl)
> u16 brightness;
> int ret;
>
> - ret = mipi_dsi_dcs_get_display_brightness(dsi, &brightness);
> + ret = mipi_dsi_dcs_get_display_brightness(dsi, &brightness, 1);
> if (ret < 0)
> return ret;
>
> diff --git a/include/drm/drm_mipi_dsi.h b/include/drm/drm_mipi_dsi.h
> index 4f503d99f668..da02f09f251b 100644
> --- a/include/drm/drm_mipi_dsi.h
> +++ b/include/drm/drm_mipi_dsi.h
> @@ -293,9 +293,9 @@ int mipi_dsi_dcs_set_tear_on(struct mipi_dsi_device *dsi,
> int mipi_dsi_dcs_set_pixel_format(struct mipi_dsi_device *dsi, u8 format);
> int mipi_dsi_dcs_set_tear_scanline(struct mipi_dsi_device *dsi, u16 scanline);
> int mipi_dsi_dcs_set_display_brightness(struct mipi_dsi_device *dsi,
> - u16 brightness);
> + u16 brightness, size_t num_params);
> int mipi_dsi_dcs_get_display_brightness(struct mipi_dsi_device *dsi,
> - u16 *brightness);
> + u16 *brightness, size_t num_params);
>
> /**
> * mipi_dsi_generic_write_seq - transmit data using a generic write packet
> --
> 2.39.0

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In reply to: Richard Acayan: "Re: [RFC PATCH] drm/dsi-mipi: Fix byte order of DCS set/get brightness"
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