[PATCH] drm/edid: Fix off-by-one in DispID DTD pixel clock

[PATCH] drm/edid: Fix off-by-one in DispID DTD pixel clock

[Ville Syrjala]

From: Ville Syrjälä <ville.syrjala@linux.intel.com>

The DispID DTD pixel clock is documented as:
"00 00 00 h → FF FF FF h | Pixel clock ÷ 10,000 0.01 → 167,772.16 Mega Pixels per Sec"
Which seems to imply that we to add one to the raw value.

Reality seems to agree as there are tiled displays in the wild
which currently show a 10kHz difference in the pixel clock
between the tiles (one tile gets its mode from the base EDID,
the other from the DispID block).

Cc: stable@vger.kernel.org
References: https://gitlab.freedesktop.org/drm/intel/-/issues/27
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
---
 drivers/gpu/drm/drm_edid.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 43b6ca364daa..544d2603f5fc 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -5120,7 +5120,7 @@ static struct drm_display_mode *drm_mode_displayid_detailed(struct drm_device *d
 	struct drm_display_mode *mode;
 	unsigned pixel_clock = (timings->pixel_clock[0] |
 				(timings->pixel_clock[1] << 8) |
-				(timings->pixel_clock[2] << 16));
+				(timings->pixel_clock[2] << 16)) + 1;
 	unsigned hactive = (timings->hactive[0] | timings->hactive[1] << 8) + 1;
 	unsigned hblank = (timings->hblank[0] | timings->hblank[1] << 8) + 1;
 	unsigned hsync = (timings->hsync[0] | (timings->hsync[1] & 0x7f) << 8) + 1;
-- 
2.24.1

Re: [Intel-gfx] [PATCH] drm/edid: Fix off-by-one in DispID DTD pixel clock

[Manasi Navare]

On Thu, Apr 23, 2020 at 06:17:43PM +0300, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> The DispID DTD pixel clock is documented as:
> "00 00 00 h → FF FF FF h | Pixel clock ÷ 10,000 0.01 → 167,772.16 Mega Pixels per Sec"
> Which seems to imply that we to add one to the raw value.
> 
> Reality seems to agree as there are tiled displays in the wild
> which currently show a 10kHz difference in the pixel clock
> between the tiles (one tile gets its mode from the base EDID,
> the other from the DispID block).
> 
> Cc: stable@vger.kernel.org
> References: https://gitlab.freedesktop.org/drm/intel/-/issues/27
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Makes total sense,

Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>

Manasi

> ---
>  drivers/gpu/drm/drm_edid.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 43b6ca364daa..544d2603f5fc 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -5120,7 +5120,7 @@ static struct drm_display_mode *drm_mode_displayid_detailed(struct drm_device *d
>  	struct drm_display_mode *mode;
>  	unsigned pixel_clock = (timings->pixel_clock[0] |
>  				(timings->pixel_clock[1] << 8) |
> -				(timings->pixel_clock[2] << 16));
> +				(timings->pixel_clock[2] << 16)) + 1;
>  	unsigned hactive = (timings->hactive[0] | timings->hactive[1] << 8) + 1;
>  	unsigned hblank = (timings->hblank[0] | timings->hblank[1] << 8) + 1;
>  	unsigned hsync = (timings->hsync[0] | (timings->hsync[1] & 0x7f) << 8) + 1;
> -- 
> 2.24.1
> 
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx