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Subject[PATCH 5.10 295/599] drm/bridge: dw-hdmi: use safe format when first in bridge chain
From: Neil Armstrong <>

[ Upstream commit 1528038385c0a706aac9ac165eeb24044fef6825 ]

When the dw-hdmi bridge is in first place of the bridge chain, this
means there is no way to select an input format of the dw-hdmi HW

Since introduction of display-connector, negotiation was broken since
the dw-hdmi negotiation code only worked when the dw-hdmi bridge was
in last position of the bridge chain or behind another bridge also
supporting input & output format negotiation.

Commit 7cd70656d128 ("drm/bridge: display-connector: implement bus fmts callbacks")
was introduced to make negotiation work again by making display-connector
act as a pass-through concerning input & output format negotiation.

But in the case where the dw-hdmi is single in the bridge chain, for
example on Renesas SoCs, with the display-connector bridge the dw-hdmi
is no more single, breaking output format.

Reported-by: Biju Das <>
Bisected-by: Kieran Bingham <>
Tested-by: Kieran Bingham <>
Fixes: 6c3c719936da ("drm/bridge: synopsys: dw-hdmi: add bus format negociation")
Signed-off-by: Neil Armstrong <>
[narmstrong: add proper fixes commit]
Reviewed-by: Robert Foss <>
Signed-off-by: Sasha Levin <>
drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
index 29c0eb4bd754..b10228b9e3a9 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
@@ -2566,8 +2566,9 @@ static u32 *dw_hdmi_bridge_atomic_get_output_bus_fmts(struct drm_bridge *bridge,
if (!output_fmts)
return NULL;

- /* If dw-hdmi is the only bridge, avoid negociating with ourselves */
- if (list_is_singular(&bridge->encoder->bridge_chain)) {
+ /* If dw-hdmi is the first or only bridge, avoid negociating with ourselves */
+ if (list_is_singular(&bridge->encoder->bridge_chain) ||
+ list_is_first(&bridge->chain_node, &bridge->encoder->bridge_chain)) {
*num_output_fmts = 1;
output_fmts[0] = MEDIA_BUS_FMT_FIXED;


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