linux-kernel - [PATCH 5.16 0493/1017] drm/bridge: dw-hdmi: use safe format when first in bridge chain

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Message-Id: <20220405070408.933296758@linuxfoundation.org>
Date:   Tue,  5 Apr 2022 09:23:26 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Biju Das <biju.das.jz@...renesas.com>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.16 0493/1017] drm/bridge: dw-hdmi: use safe format when first in bridge chain

From: Neil Armstrong <narmstrong@...libre.com>

[ 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
component.

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 <biju.das.jz@...renesas.com>
Bisected-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
Tested-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
Fixes: 6c3c719936da ("drm/bridge: synopsys: dw-hdmi: add bus format negociation")
Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
[narmstrong: add proper fixes commit]
Reviewed-by: Robert Foss <robert.foss@...aro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220204143337.89221-1-narmstrong@baylibre.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 e1211a5b334b..25d58dcfc87e 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
@@ -2551,8 +2551,9 @@ 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;
 
-- 
2.34.1