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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Tomeu Vizoso <tomeu.vizoso@collabora.com>,
        Brian Norris <briannorris@chromium.org>,
        Douglas Anderson <dianders@chromium.org>
Subject: [PATCH 4.19 162/287] drm/bridge: analogix_dp: Grab runtime PM reference for DP-AUX
Date:   Mon, 13 Jun 2022 12:09:46 +0200
Message-Id: <20220613094928.790591935@linuxfoundation.org>
In-Reply-To: <20220613094923.832156175@linuxfoundation.org>
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From: Brian Norris <briannorris@chromium.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@vger.kernel.org>
Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Signed-off-by: Brian Norris <briannorris@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220301181107.v4.1.I773a08785666ebb236917b0c8e6c05e3de471e75@changeid
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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
@@ -1514,8 +1514,19 @@ 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 *