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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Aug 23, 2022 at 08:15:48PM +0300, Jani Nikula wrote:
> 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*.

Yeah, I figured that writing the code in the most straightforward
way was fine since reserved values aren't going to produce valid
results anyway. Though I guess just ignoring the whole descriptor
in that case might be another option.

> 
> 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.

Derp.

> 
> With that fixed, whether or not you decide to do anything about the
> nitpicks,
>
> Reviewed-by: Jani Nikula <jani.nikula@intel.com>

Thanks.

> 
> 
> 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

-- 
Ville Syrjälä
Intel