[PATCH v2] drm/bridge: analogix_dp: Grab runtime PM reference for DP-AUX

[Brian Norris <briannorris@chromium.org>]

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 the panel and PM state right before trying to talk AUX.

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>
---

Changes in v2:
- Fix spelling in Subject
- DRM_DEV_ERROR() -> drm_err()
- Propagate errors from un-analogix_dp_prepare_panel()

 .../drm/bridge/analogix/analogix_dp_core.c    | 21 ++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
index b7d2e4449cfa..6fc46ac93ef8 100644
--- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
+++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
@@ -1632,8 +1632,27 @@ static ssize_t analogix_dpaux_transfer(struct drm_dp_aux *aux,
 				       struct drm_dp_aux_msg *msg)
 {
 	struct analogix_dp_device *dp = to_dp(aux);
+	int ret, ret2;
 
-	return analogix_dp_transfer(dp, msg);
+	ret = analogix_dp_prepare_panel(dp, true, false);
+	if (ret) {
+		drm_err(dp->drm_dev, "Failed to prepare panel (%d)\n", ret);
+		return ret;
+	}
+
+	pm_runtime_get_sync(dp->dev);
+	ret = analogix_dp_transfer(dp, msg);
+	pm_runtime_put(dp->dev);
+
+	ret2 = analogix_dp_prepare_panel(dp, false, false);
+	if (ret2) {
+		drm_err(dp->drm_dev, "Failed to unprepare panel (%d)\n", ret2);
+		/* Prefer the analogix_dp_transfer() error, if it exists. */
+		if (!ret)
+			ret = ret2;
+	}
+
+	return ret;
 }
 
 struct analogix_dp_device *
-- 
2.33.0.800.g4c38ced690-goog