linux-kernel - [RFC][PATCH 2/2] drm/bridge: lt9611: Use both bits for HDMI sensing

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Message-Id: <20220430064828.2470989-2-jstultz@google.com>
Date:   Sat, 30 Apr 2022 06:48:28 +0000
From:   John Stultz <jstultz@...gle.com>
To:     linux-kernel@...r.kernel.org
Cc:     John Stultz <jstultz@...gle.com>,
        Yongqin Liu <yongqin.liu@...aro.org>,
        Amit Pundir <amit.pundir@...aro.org>,
        Peter Collingbourne <pcc@...gle.com>,
        Vinod Koul <vkoul@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Robert Foss <robert.foss@...aro.org>, kernel-team@...roid.com
Subject: [RFC][PATCH 2/2] drm/bridge: lt9611: Use both bits for HDMI sensing

In commit 19cf41b64e3b ("lontium-lt9611: check a different
register bit for HDMI sensing"), the bit flag used to detect
HDMI cable connect was switched from BIT(2) to BIT(0) to improve
compatibility with some monitors that didn't seem to set BIT(2).

However, with that change, I've seen occasional issues where the
detection failed, because BIT(2) was set, but not BIT(0).

Unfortunately, as I understand it, the bits and their function
was never clearly documented. So lets instead check both
(BIT(2) | BIT(0)) when checking the register.

Cc: Yongqin Liu <yongqin.liu@...aro.org>
Cc: Amit Pundir <amit.pundir@...aro.org>
Cc: Peter Collingbourne <pcc@...gle.com>
Cc: Vinod Koul <vkoul@...nel.org>
Cc: Bjorn Andersson <bjorn.andersson@...aro.org>
Cc: Robert Foss <robert.foss@...aro.org>
Cc: kernel-team@...roid.com
Signed-off-by: John Stultz <jstultz@...gle.com>
---
 drivers/gpu/drm/bridge/lontium-lt9611.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/lontium-lt9611.c b/drivers/gpu/drm/bridge/lontium-lt9611.c
index bf66af668f61..a11604a56e08 100644
--- a/drivers/gpu/drm/bridge/lontium-lt9611.c
+++ b/drivers/gpu/drm/bridge/lontium-lt9611.c
@@ -584,7 +584,7 @@ static enum drm_connector_status __lt9611_detect(struct lt9611 *lt9611)
 	int connected = 0;
 
 	regmap_read(lt9611->regmap, 0x825e, &reg_val);
-	connected  = (reg_val & BIT(0));
+	connected  = (reg_val & (BIT(2) | BIT(0)));
 
 	lt9611->status = connected ?  connector_status_connected :
 				connector_status_disconnected;
-- 
2.36.0.464.gb9c8b46e94-goog