Re: [PATCH v5 3/4] drm/bridge: analogix_dp: Add validation for samsung,lane-count property

[Luca Ceresoli]

On Thu, 04 Jun 2026 16:52:19 +0800, Damon Ding <damon.ding@xxxxxxxxxxxxxx> wrote:

Hello Damon,

>
> diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> index 7a85774aaac1..e120ef3320c1 100644
> --- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> +++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> @@ -1261,8 +1262,11 @@ static int analogix_dp_dt_parse_pdata(struct analogix_dp_device *dp)
>  		 */
>  		of_property_read_u32(dp_node, "samsung,link-rate",
>  				     &video_info->max_link_rate);
> -		of_property_read_u32(dp_node, "samsung,lane-count",
> -				     &video_info->max_lane_count);
> +		ret = of_property_read_u32(dp_node, "samsung,lane-count",
> +					   &video_info->max_lane_count);
> +		if (ret || !drm_dp_lane_count_is_valid(video_info->max_lane_count))
> +			return dev_err_probe(dp->dev, ret ? ret : -EINVAL,
> +					     "failed to parse samsung,lane-count\n");

I think this report by sashiko makes sense:

  >  sashiko-bot@xxxxxxxxxx <sashiko-bot@xxxxxxxxxx>:
  >
  >  [Severity: High]
  >  Does this make the optional and deprecated samsung,lane-count property a
  >  strict requirement?
  >
  >  If samsung,lane-count is absent from the device tree, of_property_read_u32()
  >  returns -EINVAL. This causes the condition to evaluate to true, aborting the
  >  probe with an error.
  >
  >  According to the device tree bindings
  >  (Documentation/devicetree/bindings/display/samsung/samsung,exynos5-dp.yaml),
  >  this property is marked as deprecated and explicitly optional because the
  >  lane count can be read from the monitor. Does this patch break compatibility
  >  with device trees that rightfully omit this deprecated property?

 (via: https://patch.msgid.link/20260604090935.7FC051F00898@xxxxxxxxxxxxxxx)

Can you comment on this?

Luca

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com