[PATCH 0/2] drm/panel: visionox-r66451: Fix brightness and power on

[PATCH 0/2] drm/panel: visionox-r66451: Fix brightness and power on

[Vladimir Zapolskiy]

Two fixes for the Visionox R66451 panel driver, found while enabling the
panel on the Qualcomm SM8350-HDK display card.

The first change sends the DCS brightness value MSB first, as the panel
expects. Without it, the brightness does not follow the requested value,
and the default brightness is received as a different value.

The second change waits longer after the panel reset. With the current
10ms delay, the panel misses the initialization commands, does not exit
sleep mode, and the display stays black.

Vladimir Zapolskiy (2):
  drm/panel: visionox-r66451: Send the brightness value MSB first
  drm/panel: visionox-r66451: Wait longer after the panel reset

 drivers/gpu/drm/panel/panel-visionox-r66451.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

-- 
2.51.0

[PATCH 1/2] drm/panel: visionox-r66451: Send the brightness value MSB first

[Vladimir Zapolskiy]

The panel expects to get two bytes of the DCS Set Display Brightness
command with the most significant byte first, and it uses the lower
12 bits of the value, use mipi_dsi_dcs_set_display_brightness_large()
to correct the programmed brightness values.

Tested on the SM8350-HDK display card, the display brightness increases
gradually with:

  for v in $(seq 16 16 4095); do sleep 0.1; \
    echo $v > /sys/class/backlight/ae94000.dsi.0/brightness; \
  done

while without the change the display is dark during all writes.

Fixes: a6dfab2738fc ("drm/panel: Add driver for Visionox r66451 panel")
Signed-off-by: Vladimir Zapolskiy <vz@kernel.org>
---
 drivers/gpu/drm/panel/panel-visionox-r66451.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/panel/panel-visionox-r66451.c b/drivers/gpu/drm/panel/panel-visionox-r66451.c
index 1efb139bb711..4f28bd3b6080 100644
--- a/drivers/gpu/drm/panel/panel-visionox-r66451.c
+++ b/drivers/gpu/drm/panel/panel-visionox-r66451.c
@@ -227,7 +227,7 @@ static int visionox_r66451_bl_update_status(struct backlight_device *bl)
 	struct mipi_dsi_device *dsi = bl_get_data(bl);
 	u16 brightness = backlight_get_brightness(bl);
 
-	return mipi_dsi_dcs_set_display_brightness(dsi, brightness);
+	return mipi_dsi_dcs_set_display_brightness_large(dsi, brightness);
 }
 
 static const struct backlight_ops visionox_r66451_bl_ops = {
-- 
2.51.0

Re: [PATCH 1/2] drm/panel: visionox-r66451: Send the brightness value MSB first

[Neil Armstrong]

On 11/1/26 22:24, Vladimir Zapolskiy wrote:
> The panel expects to get two bytes of the DCS Set Display Brightness
> command with the most significant byte first, and it uses the lower
> 12 bits of the value, use mipi_dsi_dcs_set_display_brightness_large()
> to correct the programmed brightness values.
> 
> Tested on the SM8350-HDK display card, the display brightness increases
> gradually with:
> 
>    for v in $(seq 16 16 4095); do sleep 0.1; \
>      echo $v > /sys/class/backlight/ae94000.dsi.0/brightness; \
>    done
> 
> while without the change the display is dark during all writes.
> 
> Fixes: a6dfab2738fc ("drm/panel: Add driver for Visionox r66451 panel")
> Signed-off-by: Vladimir Zapolskiy <vz@kernel.org>
> ---
>   drivers/gpu/drm/panel/panel-visionox-r66451.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panel/panel-visionox-r66451.c b/drivers/gpu/drm/panel/panel-visionox-r66451.c
> index 1efb139bb711..4f28bd3b6080 100644
> --- a/drivers/gpu/drm/panel/panel-visionox-r66451.c
> +++ b/drivers/gpu/drm/panel/panel-visionox-r66451.c
> @@ -227,7 +227,7 @@ static int visionox_r66451_bl_update_status(struct backlight_device *bl)
>   	struct mipi_dsi_device *dsi = bl_get_data(bl);
>   	u16 brightness = backlight_get_brightness(bl);
>   
> -	return mipi_dsi_dcs_set_display_brightness(dsi, brightness);
> +	return mipi_dsi_dcs_set_display_brightness_large(dsi, brightness);
>   }
>   
>   static const struct backlight_ops visionox_r66451_bl_ops = {

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>

Thanks,
Neil

[PATCH 2/2] drm/panel: visionox-r66451: Wait longer after the panel reset

[Vladimir Zapolskiy]

The initialization sequence is sent 10ms after the panel reset is
deasserted, however on the SM8350-HDK display card the panel does not
answer a DCS read at that time, as a result the panel initialization
commands are lost, and the panel does not exit sleep mode and the display
stays black. With the first command sent about 15ms after the reset
the panel comes up reliably, so wait 20ms after deasserting the reset.

Fixes: a6dfab2738fc ("drm/panel: Add driver for Visionox r66451 panel")
Signed-off-by: Vladimir Zapolskiy <vz@kernel.org>
---
 drivers/gpu/drm/panel/panel-visionox-r66451.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/panel/panel-visionox-r66451.c b/drivers/gpu/drm/panel/panel-visionox-r66451.c
index 4f28bd3b6080..b0559e8b1cb5 100644
--- a/drivers/gpu/drm/panel/panel-visionox-r66451.c
+++ b/drivers/gpu/drm/panel/panel-visionox-r66451.c
@@ -36,7 +36,7 @@ static void visionox_r66451_reset(struct visionox_r66451 *ctx)
 	gpiod_set_value_cansleep(ctx->reset_gpio, 1);
 	usleep_range(10000, 10100);
 	gpiod_set_value_cansleep(ctx->reset_gpio, 0);
-	usleep_range(10000, 10100);
+	usleep_range(20000, 21000);
 }
 
 static int visionox_r66451_on(struct visionox_r66451 *ctx)
-- 
2.51.0

Re: [PATCH 2/2] drm/panel: visionox-r66451: Wait longer after the panel reset

[Neil Armstrong]

On 11/1/26 22:24, Vladimir Zapolskiy wrote:
> The initialization sequence is sent 10ms after the panel reset is
> deasserted, however on the SM8350-HDK display card the panel does not
> answer a DCS read at that time, as a result the panel initialization
> commands are lost, and the panel does not exit sleep mode and the display
> stays black. With the first command sent about 15ms after the reset
> the panel comes up reliably, so wait 20ms after deasserting the reset.
> 
> Fixes: a6dfab2738fc ("drm/panel: Add driver for Visionox r66451 panel")
> Signed-off-by: Vladimir Zapolskiy <vz@kernel.org>
> ---
>   drivers/gpu/drm/panel/panel-visionox-r66451.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panel/panel-visionox-r66451.c b/drivers/gpu/drm/panel/panel-visionox-r66451.c
> index 4f28bd3b6080..b0559e8b1cb5 100644
> --- a/drivers/gpu/drm/panel/panel-visionox-r66451.c
> +++ b/drivers/gpu/drm/panel/panel-visionox-r66451.c
> @@ -36,7 +36,7 @@ static void visionox_r66451_reset(struct visionox_r66451 *ctx)
>   	gpiod_set_value_cansleep(ctx->reset_gpio, 1);
>   	usleep_range(10000, 10100);
>   	gpiod_set_value_cansleep(ctx->reset_gpio, 0);
> -	usleep_range(10000, 10100);
> +	usleep_range(20000, 21000);
>   }
>   
>   static int visionox_r66451_on(struct visionox_r66451 *ctx)

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>

Thanks,
Neil

Re: [PATCH 0/2] drm/panel: visionox-r66451: Fix brightness and power on

[Neil Armstrong]

Hi,

On Sun, 01 Nov 2026 23:24:56 +0200, Vladimir Zapolskiy wrote:
> Two fixes for the Visionox R66451 panel driver, found while enabling the
> panel on the Qualcomm SM8350-HDK display card.
> 
> The first change sends the DCS brightness value MSB first, as the panel
> expects. Without it, the brightness does not follow the requested value,
> and the default brightness is received as a different value.
> 
> [...]

Thanks, Applied to https://gitlab.freedesktop.org/drm/misc/kernel.git (drm-misc-fixes)

[1/2] drm/panel: visionox-r66451: Send the brightness value MSB first
      https://gitlab.freedesktop.org/drm/misc/kernel/-/commit/00fe6be187ffde738fdb71ea7deb671fc939e583
[2/2] drm/panel: visionox-r66451: Wait longer after the panel reset
      https://gitlab.freedesktop.org/drm/misc/kernel/-/commit/b4b2778d5e175b166e4a27e5df5d61da468ad004

-- 
Neil