Re: [PATCH v14 5/9] drm/bridge: dw-hdmi: repair interworking with hdmi-connector for jz4780

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Hi Nikolaus,


Le sam., févr. 12 2022 at 15:19:23 +0100, H. Nikolaus Schaller <hns@xxxxxxxxxxxxx> a écrit :
Commit 7cd70656d1285b ("drm/bridge: display-connector: implement bus fmts callbacks")

introduced a new mechanism to negotiate bus formats between hdmi connector
and the synopsys hdmi driver inside the jz4780.

By this, the dw-hdmi is no longer the only bridge and sets up a list
of formats in dw_hdmi_bridge_atomic_get_output_bus_fmts().

This includes MEDIA_BUS_FMT_UYVY8_1X16 which is chosen for the jz4780 but only
produces a black screen.

Neil pushed a fix yesterday that looks like it could fix your issue.
The fix is: 1528038385c0 ("drm/bridge: dw-hdmi: use safe format when first in bridge chain")

Could you try if it does indeed fix your issue?

Cheers,
-Paul

This fix is based on the observation that max_bpc = 0 when running this function while info->bpc = 8. Since the formats checks before this always test for max_bpc >= info->pbc indirectly my assumption is that we must check it
here as well.

Adding the proposed patch makes the CI20/jz4780 panel work again in
MEDIA_BUS_FMT_RGB888_1X24 mode.

Fixes: 7cd70656d1285b ("drm/bridge: display-connector: implement bus fmts callbacks")
Signed-off-by: H. Nikolaus Schaller <hns@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
index b0d8110dd412c..826a055a7a273 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
@@ -2620,10 +2620,10 @@ static u32 *dw_hdmi_bridge_atomic_get_output_bus_fmts(struct drm_bridge *bridge,
 		output_fmts[i++] = MEDIA_BUS_FMT_RGB101010_1X30;
 	}

-	if (info->color_formats & DRM_COLOR_FORMAT_YCBCR422)
+ if (max_bpc >= info->bpc && info->color_formats & DRM_COLOR_FORMAT_YCBCR422)
 		output_fmts[i++] = MEDIA_BUS_FMT_UYVY8_1X16;

-	if (info->color_formats & DRM_COLOR_FORMAT_YCBCR444)
+ if (max_bpc >= info->bpc && info->color_formats & DRM_COLOR_FORMAT_YCBCR444)
 		output_fmts[i++] = MEDIA_BUS_FMT_YUV8_1X24;

 	/* Default 8bit RGB fallback */
--
2.33.0






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