[PATCH] drm/bridge: adv7511: Reset registers on hotplug

[Rob Clark]

On Tue, Jul 3, 2018 at 12:56 PM, Sean Paul <seanpaul at chromium.org> wrote:
> The bridge loses its hw state when the cable is unplugged. If we detect
> this case in the hpd handler, reset its state.
>
> Reported-by: Rob Clark <robdclark at gmail.com>
> Signed-off-by: Sean Paul <seanpaul at chromium.org>

Tested-by: Rob Clark <robdclark at gmail.com>

> ---
> This is the follow-up to "drm/msm: Disable mdp5 crtc when there are no
> active planes". I incorrectly assumed the modeset was required from the
> msm side, but Rob pointed out that he thought it might be a bridge
> issue.

To elaborate, this is an atomic userspace (weston), when it sees the
display disconnected, it removes the planes from the CRTC but does not
disable the CRTC.  So drm/msm sets up the LM to scanout a solid color,
and leaves the encoder and dsi cranking along happily.  When
replugging the display, the atomic helpers see the CRTC is still
active and (correctly) doesn't do a full modeset.  So the bridge is
not re-configured/re-enabled.

Arguably this perhaps isn't what weston *wanted* to do, but in the end
the bug is in the bridge.

We could possibly set the connector link_status to BAD as an
alternative.  But at least the build of weston I'm using atm doesn't
handle the link_status propery, this approach requires each atomic
userspace to handle this case.  Compared to Sean's approach which is
transparent to userspace, which seems attractive.

BR,
-R

>
>  drivers/gpu/drm/bridge/adv7511/adv7511_drv.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> index 73021b388e12..dd3ff2f2cdce 100644
> --- a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> +++ b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> @@ -429,6 +429,18 @@ static void adv7511_hpd_work(struct work_struct *work)
>         else
>                 status = connector_status_disconnected;
>
> +       /*
> +        * The bridge resets its registers on unplug. So when we get a plug
> +        * event and we're already supposed to be powered, cycle the bridge to
> +        * restore its state.
> +        */
> +       if (status == connector_status_connected &&
> +           adv7511->connector.status == connector_status_disconnected &&
> +           adv7511->powered) {
> +               regcache_mark_dirty(adv7511->regmap);
> +               adv7511_power_on(adv7511);
> +       }
> +
>         if (adv7511->connector.status != status) {
>                 adv7511->connector.status = status;
>                 if (status == connector_status_disconnected)
> --
> Sean Paul, Software Engineer, Google / Chromium OS
>