Re: [PATCH] drm/edid: Handle EDID 1.4 range descriptor h/vfreq offsets

[Jani Nikula <jani.nikula@linux.intel.com>]

On Fri, 19 Aug 2022, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> EDID 1.4 introduced some extra flags in the range
> descriptor to support min/max h/vfreq >= 255. Consult them
> to correctly parse the vfreq limits.
>
> Cc: stable@vger.kernel.org
> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/6519
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/drm_edid.c | 24 ++++++++++++++++++------
>  include/drm/drm_edid.h     |  5 +++++
>  2 files changed, 23 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 90a5e26eafa8..4005dab6147d 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -6020,12 +6020,14 @@ static void drm_parse_cea_ext(struct drm_connector *connector,
>  }
>  
>  static
> -void get_monitor_range(const struct detailed_timing *timing,
> -		       void *info_monitor_range)
> +void get_monitor_range(const struct detailed_timing *timing, void *c)
>  {
> -	struct drm_monitor_range_info *monitor_range = info_monitor_range;
> +	struct detailed_mode_closure *closure = c;
> +	struct drm_display_info *info = &closure->connector->display_info;
> +	struct drm_monitor_range_info *monitor_range = &info->monitor_range;
>  	const struct detailed_non_pixel *data = &timing->data.other_data;
>  	const struct detailed_data_monitor_range *range = &data->data.range;
> +	const struct edid *edid = closure->drm_edid->edid;
>  
>  	if (!is_display_descriptor(timing, EDID_DETAIL_MONITOR_RANGE))
>  		return;
> @@ -6041,18 +6043,28 @@ void get_monitor_range(const struct detailed_timing *timing,
>  
>  	monitor_range->min_vfreq = range->min_vfreq;
>  	monitor_range->max_vfreq = range->max_vfreq;
> +
> +	if (edid->revision >= 4) {
> +		if (data->pad2 & DRM_EDID_RANGE_OFFSET_MIN_VFREQ)
> +			monitor_range->min_vfreq += 255;
> +		if (data->pad2 & DRM_EDID_RANGE_OFFSET_MAX_VFREQ)
> +			monitor_range->max_vfreq += 255;
> +	}

Nitpick, a combo where min vertical range has +255 offset but max
doesn't shouldn't be okay. But then, what are we going to do in that
case anyway? I guess the generic check would be min <= max. Also, the
+255 offset range is 256..510, not 256..(255+255). Again, what to do if
that's what the EDID has? *shrug*.

Anyway, what's broken here (and probably impacts the testing in the
referenced bug) is that the struct drm_monitor_range_info members are u8
and this overflows.

With that fixed, whether or not you decide to do anything about the
nitpicks,

Reviewed-by: Jani Nikula <jani.nikula@intel.com>


Side note, git grep for monitor_range reveals amdgpu are doing their own
thing for the parsing. *sigh*.


>  }
>  
>  static void drm_get_monitor_range(struct drm_connector *connector,
>  				  const struct drm_edid *drm_edid)
>  {
> -	struct drm_display_info *info = &connector->display_info;
> +	const struct drm_display_info *info = &connector->display_info;
> +	struct detailed_mode_closure closure = {
> +		.connector = connector,
> +		.drm_edid = drm_edid,
> +	};
>  
>  	if (!version_greater(drm_edid, 1, 1))
>  		return;
>  
> -	drm_for_each_detailed_block(drm_edid, get_monitor_range,
> -				    &info->monitor_range);
> +	drm_for_each_detailed_block(drm_edid, get_monitor_range, &closure);
>  
>  	DRM_DEBUG_KMS("Supported Monitor Refresh rate range is %d Hz - %d Hz\n",
>  		      info->monitor_range.min_vfreq,
> diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h
> index 2181977ae683..d81da97cad6e 100644
> --- a/include/drm/drm_edid.h
> +++ b/include/drm/drm_edid.h
> @@ -92,6 +92,11 @@ struct detailed_data_string {
>  	u8 str[13];
>  } __attribute__((packed));
>  
> +#define DRM_EDID_RANGE_OFFSET_MIN_VFREQ (1 << 0)
> +#define DRM_EDID_RANGE_OFFSET_MAX_VFREQ (1 << 1)
> +#define DRM_EDID_RANGE_OFFSET_MIN_HFREQ (1 << 2)
> +#define DRM_EDID_RANGE_OFFSET_MAX_HFREQ (1 << 3)
> +
>  #define DRM_EDID_DEFAULT_GTF_SUPPORT_FLAG   0x00
>  #define DRM_EDID_RANGE_LIMITS_ONLY_FLAG     0x01
>  #define DRM_EDID_SECONDARY_GTF_SUPPORT_FLAG 0x02

-- 
Jani Nikula, Intel Open Source Graphics Center