linux-kernel - [PATCH 5.15 015/128] drm/mediatek: hdmi: Perform NULL pointer check for mtk_hdmi

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Message-Id: <20211227151332.033041957@linuxfoundation.org>
Date:   Mon, 27 Dec 2021 16:29:50 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.15 015/128] drm/mediatek: hdmi: Perform NULL pointer check for mtk_hdmi_conf

From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>

[ Upstream commit 3b8e19a0aa3933a785be9f1541afd8d398c4ec69 ]

In commit 41ca9caaae0b
("drm/mediatek: hdmi: Add check for CEA modes only") a check
for CEA modes was added to function mtk_hdmi_bridge_mode_valid()
in order to address possible issues on MT8167;
moreover, with commit c91026a938c2
("drm/mediatek: hdmi: Add optional limit on maximal HDMI mode clock")
another similar check was introduced.

Unfortunately though, at the time of writing, MT8173 does not provide
any mtk_hdmi_conf structure and this is crashing the kernel with NULL
pointer upon entering mtk_hdmi_bridge_mode_valid(), which happens as
soon as a HDMI cable gets plugged in.

To fix this regression, add a NULL pointer check for hdmi->conf in the
said function, restoring HDMI functionality and avoiding NULL pointer
kernel panics.

Fixes: 41ca9caaae0b ("drm/mediatek: hdmi: Add check for CEA modes only")
Fixes: c91026a938c2 ("drm/mediatek: hdmi: Add optional limit on maximal HDMI mode clock")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/gpu/drm/mediatek/mtk_hdmi.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_hdmi.c b/drivers/gpu/drm/mediatek/mtk_hdmi.c
index 5838c44cbf6f0..3196189429bcf 100644
--- a/drivers/gpu/drm/mediatek/mtk_hdmi.c
+++ b/drivers/gpu/drm/mediatek/mtk_hdmi.c
@@ -1224,12 +1224,14 @@ static int mtk_hdmi_bridge_mode_valid(struct drm_bridge *bridge,
 			return MODE_BAD;
 	}
 
-	if (hdmi->conf->cea_modes_only && !drm_match_cea_mode(mode))
-		return MODE_BAD;
+	if (hdmi->conf) {
+		if (hdmi->conf->cea_modes_only && !drm_match_cea_mode(mode))
+			return MODE_BAD;
 
-	if (hdmi->conf->max_mode_clock &&
-	    mode->clock > hdmi->conf->max_mode_clock)
-		return MODE_CLOCK_HIGH;
+		if (hdmi->conf->max_mode_clock &&
+		    mode->clock > hdmi->conf->max_mode_clock)
+			return MODE_CLOCK_HIGH;
+	}
 
 	if (mode->clock < 27000)
 		return MODE_CLOCK_LOW;
-- 
2.34.1