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

stable inclusion
from stable-v5.10.121
commit 495ac7757663c6b61ffa5b7442285629f387a0a6
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5L6CQ

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=495ac7757663c6b61ffa5b7442285629f387a0a6



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commit 8fb6c44f 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: 0d97ad03 ("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>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Acked-by: Xie XiuQi <xiexiuqi@huawei.com>