The bridge might miss the display change events when it's powered off.
This happens when a user changes the external monitor when the system
is suspended and the embedded controller doesn't not wake AP up.

It's also observed that one DP-to-HDMI bridge doesn't work correctly
when there is no EDID read after it is powered on.

Drop the cache to force an EDID read after system resume to fix this.

Fixes: 11feaef69d0c ("drm/bridge: it6505: Add caching for EDID")
Signed-off-by: Pin-yen Lin <treapking@chromium.org>

---

 drivers/gpu/drm/bridge/ite-it6505.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/bridge/ite-it6505.c b/drivers/gpu/drm/bridge/ite-it6505.c
index 1e1c06fdf206..bb449efac2f4 100644
--- a/drivers/gpu/drm/bridge/ite-it6505.c
+++ b/drivers/gpu/drm/bridge/ite-it6505.c
@@ -3101,6 +3101,8 @@ static __maybe_unused int it6505_bridge_suspend(struct device *dev)
 {
 	struct it6505 *it6505 = dev_get_drvdata(dev);
 
+	it6505_remove_edid(it6505);
+
 	return it6505_poweroff(it6505);
 }
 
-- 
2.46.0.792.g87dc391469-goog

Hi,

On Mon, Sep 23, 2024 at 8:53 PM Pin-yen Lin <treapking@chromium.org> wrote:
>
> The bridge might miss the display change events when it's powered off.
> This happens when a user changes the external monitor when the system
> is suspended and the embedded controller doesn't not wake AP up.
>
> It's also observed that one DP-to-HDMI bridge doesn't work correctly
> when there is no EDID read after it is powered on.
>
> Drop the cache to force an EDID read after system resume to fix this.
>
> Fixes: 11feaef69d0c ("drm/bridge: it6505: Add caching for EDID")
> Signed-off-by: Pin-yen Lin <treapking@chromium.org>

Ah, I guess this answers my question in the previous patch about
whether caching was important even for external displays since this
driver only supports external DP and the commit you mention in "Fixes"
says that caching was important.

So this looks reasonable. One thing I wonder is if you're totally
guaranteed to get a PM Runtime suspend whenever you get an unplug /
replug of a display. I tried to dig a little bit but I'm not super
familiar with this bridge and it looks complicated enough that I guess
I'll have to trust that it's fine. So...

Reviewed-by: Douglas Anderson <dianders@chromium.org>

Hi,

On Wed, Sep 25, 2024 at 1:48 AM Doug Anderson <dianders@chromium.org> wrote:
>
> Hi,
>
> On Mon, Sep 23, 2024 at 8:53 PM Pin-yen Lin <treapking@chromium.org> wrote:
> >
> > The bridge might miss the display change events when it's powered off.
> > This happens when a user changes the external monitor when the system
> > is suspended and the embedded controller doesn't not wake AP up.
> >
> > It's also observed that one DP-to-HDMI bridge doesn't work correctly
> > when there is no EDID read after it is powered on.
> >
> > Drop the cache to force an EDID read after system resume to fix this.
> >
> > Fixes: 11feaef69d0c ("drm/bridge: it6505: Add caching for EDID")
> > Signed-off-by: Pin-yen Lin <treapking@chromium.org>
>
> Ah, I guess this answers my question in the previous patch about
> whether caching was important even for external displays since this
> driver only supports external DP and the commit you mention in "Fixes"
> says that caching was important.
>
> So this looks reasonable. One thing I wonder is if you're totally
> guaranteed to get a PM Runtime suspend whenever you get an unplug /
> replug of a display. I tried to dig a little bit but I'm not super
> familiar with this bridge and it looks complicated enough that I guess
> I'll have to trust that it's fine. So...

it6505_remove_edid() is also called when the bridge reads HPD low in
the IRQ handler or the DPCD sink count changes to 0 after a HPD_IRQ
signal. The assumption here is that if the bridge is still powered on,
then it should be aware of the monitor change events and drop the EDID
cache when needed. This patch addresses the scenario where monitor
changes are not communicated to the bridge when it is powered off.
>
> Reviewed-by: Douglas Anderson <dianders@chromium.org>

Regards,
Pin-yen

On Tue, Sep 24, 2024 at 11:51:47AM GMT, Pin-yen Lin wrote:
> The bridge might miss the display change events when it's powered off.
> This happens when a user changes the external monitor when the system
> is suspended and the embedded controller doesn't not wake AP up.
> 
> It's also observed that one DP-to-HDMI bridge doesn't work correctly
> when there is no EDID read after it is powered on.
> 
> Drop the cache to force an EDID read after system resume to fix this.
> 
> Fixes: 11feaef69d0c ("drm/bridge: it6505: Add caching for EDID")
> Signed-off-by: Pin-yen Lin <treapking@chromium.org>
> 
> ---
> 
>  drivers/gpu/drm/bridge/ite-it6505.c | 2 ++
>  1 file changed, 2 insertions(+)
> 

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

-- 
With best wishes
Dmitry