Hi,
On 26/02/2022 18:13, H. Nikolaus Schaller wrote:
Commit 7cd70656d1285b ("drm/bridge: display-connector: implement bus fmts callbacks")
introduced a new mechanism to negotiate bus formats between hdmi connectors
and bridges which is to be used e.g. for the jz4780 based CI20 board.
In this case dw-hdmi sets up a list of formats in
dw_hdmi_bridge_atomic_get_output_bus_fmts().
This includes e.g. MEDIA_BUS_FMT_UYVY8_1X16 which is chosen for the CI20 but
only produces a black screen.
Analysis revealed an omission in
Commit 6c3c719936dafe ("drm/bridge: synopsys: dw-hdmi: add bus format negociation")
to check for 8 bit with when adding UYVY8 or YUV8 formats.
This fix is based on the observation that max_bpc = 0 when running this
function while info->bpc = 8.
In fact if bpc = 0, it should be considered as 8, so the issue is elsewhere.
Adding the proposed patch makes the jz4780/CI20 panel work again with default
MEDIA_BUS_FMT_RGB888_1X24 mode.
Fixes: 7cd70656d1285b ("drm/bridge: display-connector: implement bus fmts callbacks")
Fixes: 6c3c719936dafe ("drm/bridge: synopsys: dw-hdmi: add bus format negociation")
Signed-off-by: H. Nikolaus Schaller <hns@xxxxxxxxxxxxx>
---
drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
index 43e375da131e8..c08e2cc96584c 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
@@ -2621,11 +2621,13 @@ 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)
- output_fmts[i++] = MEDIA_BUS_FMT_UYVY8_1X16;
+ if (max_bpc >= 8 && info->bpc >= 8) {
+ if (info->color_formats & DRM_COLOR_FORMAT_YCBCR422)
+ output_fmts[i++] = MEDIA_BUS_FMT_UYVY8_1X16;
- if (info->color_formats & DRM_COLOR_FORMAT_YCBCR444)
- output_fmts[i++] = MEDIA_BUS_FMT_YUV8_1X24;
+ if (info->color_formats & DRM_COLOR_FORMAT_YCBCR444)
+ output_fmts[i++] = MEDIA_BUS_FMT_YUV8_1X24;
+ }
It should not select YUV here if it's not possible, so something is wrong.
Can you check if https://lore.kernel.org/r/20220119123656.1456355-2-narmstrong@xxxxxxxxxxxx fixes this issue instead ?
Neil
/* Default 8bit RGB fallback */
output_fmts[i++] = MEDIA_BUS_FMT_RGB888_1X24;
