drm/bridge: analogix_dp: Grab runtime PM reference for DP-AUX

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

diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
index eb590fb8e8d0dd3d7c44df18fd060f32a7213e81..d45931913dfc8de01b8c885682977002477783b9 100644 (file)
--- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
+++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
@@ -1632,8 +1632,19 @@ 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;
+
+       pm_runtime_get_sync(dp->dev);
+
+       ret = analogix_dp_detect_hpd(dp);
+       if (ret)
+               goto out;
 
-       return analogix_dp_transfer(dp, msg);
+       ret = analogix_dp_transfer(dp, msg);
+out:
+       pm_runtime_put(dp->dev);
+
+       return ret;
 }
 
 struct analogix_dp_device *