linux-kernel - [PATCH 5.4 242/411] drm/bridge: analogix_dp: Grab runtime PM reference for DP-AUX

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Message-Id: <20220613094936.035742079@linuxfoundation.org>
Date:   Mon, 13 Jun 2022 12:08:35 +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, Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Brian Norris <briannorris@...omium.org>,
        Douglas Anderson <dianders@...omium.org>
Subject: [PATCH 5.4 242/411] drm/bridge: analogix_dp: Grab runtime PM reference for DP-AUX

From: Brian Norris <briannorris@...omium.org>

commit 8fb6c44fe8468f92ac7b8bbfcca4404a4e88645f upstream.

If the display is not enable()d, then we aren't holding a runtime PM
reference here. Thus, it's easy to accidentally cause a hang, if user
space is poking around at /dev/drm_dp_aux0 at the "wrong" time.

Let's get a runtime PM reference, and check that we "see" the panel.
Don't force any panel power-up, etc., because that can be intrusive, and
that's not what other drivers do (see
drivers/gpu/drm/bridge/ti-sn65dsi86.c and
drivers/gpu/drm/bridge/parade-ps8640.c.)

Fixes: 0d97ad03f422 ("drm/bridge: analogix_dp: Remove duplicated code")
Cc: <stable@...r.kernel.org>
Cc: Tomeu Vizoso <tomeu.vizoso@...labora.com>
Signed-off-by: Brian Norris <briannorris@...omium.org>
Reviewed-by: Douglas Anderson <dianders@...omium.org>
Signed-off-by: Douglas Anderson <dianders@...omium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220301181107.v4.1.I773a08785666ebb236917b0c8e6c05e3de471e75@changeid
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/gpu/drm/bridge/analogix/analogix_dp_core.c |   13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

--- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
+++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
@@ -1630,8 +1630,19 @@ static ssize_t analogix_dpaux_transfer(s
 				       struct drm_dp_aux_msg *msg)
 {
 	struct analogix_dp_device *dp = to_dp(aux);
+	int ret;
 
-	return analogix_dp_transfer(dp, msg);
+	pm_runtime_get_sync(dp->dev);
+
+	ret = analogix_dp_detect_hpd(dp);
+	if (ret)
+		goto out;
+
+	ret = analogix_dp_transfer(dp, msg);
+out:
+	pm_runtime_put(dp->dev);
+
+	return ret;
 }
 
 struct analogix_dp_device *