Re: [PATCH 5/5] drm/bridge: ti-sn65dsi86: support booloader enabled display

Laurent Pinchart
2019-07-02T15:20:34Z

Hi Rob,

Thank you for the patch.

On Sun, Jun 30, 2019 at 08:01:43AM -0700, Rob Clark wrote:
> From: Rob Clark <robdclark@chromium.org>
>
> Request the enable gpio ASIS to avoid disabling bridge during probe, if
> already enabled. And if already enabled, defer enabling runpm until
> attach to avoid cutting off the power to the bridge.
>
> Once we get to attach, we know panel and drm driver are probed
> successfully, so at this point it i s safe to enable runpm and reset the
> bridge. If we do it earlier, we kill efifb (in the case that panel or
> drm driver do not probe successfully, giving the user no way to see what
> is going on.
>
> Signed-off-by: Rob Clark <robdclark@chromium.org>
> ---
> drivers/gpu/drm/bridge/ti-sn65dsi86.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> index 7a046bcdd81b..8bdc33576992 100644
> --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> @@ -257,6 +257,12 @@ static int ti_sn_bridge_attach(struct drm_bridge *bridge)
> .node = NULL,
> };
>
> + if (gpiod_get_value(pdata->enable_gpio)) {
> + pm_runtime_enable(pdata->dev);

Does this need to be balanced with a pm_runtime_disable() call ? Bridges
can be attached and detached at runtime when reloading the display
controller drivers, so you need to ensure that detach/re-attach cycles
work.

> + ti_sn_bridge_resume(pdata->dev);
> + ti_sn_bridge_suspend(pdata->dev);
> + }
> +
> ret = drm_connector_init(bridge->dev, &pdata->connector,
> &ti_sn_bridge_connector_funcs,
> DRM_MODE_CONNECTOR_eDP);
> @@ -813,7 +819,7 @@ static int ti_sn_bridge_probe(struct i2c_client *client,
> dev_set_drvdata(&client->dev, pdata);
>
> pdata->enable_gpio = devm_gpiod_get(pdata->dev, "enable",
> - GPIOD_OUT_LOW);
> + GPIOD_ASIS);
> if (IS_ERR(pdata->enable_gpio)) {
> DRM_ERROR("failed to get enable gpio from DT\n");
> ret = PTR_ERR(pdata->enable_gpio);
> @@ -843,7 +849,9 @@ static int ti_sn_bridge_probe(struct i2c_client *client,
> if (ret)
> return ret;
>
> - pm_runtime_enable(pdata->dev);
> + if (!gpiod_get_value(pdata->enable_gpio)) {
> + pm_runtime_enable(pdata->dev);
> + }

If I understand the issue correctly, this is part of an effort to avoid
disabling a potentially display output until we get as close as possible
to display handover, right ? Is there a drawback in always enabling
runtime PM when the bridge is attached instead of at probe time ? I
think we need to come up with a set of rules for bridge driver authors,
otherwise we'll end up with incompatible expectations of bridge drivers
and display controller drivers.

>
> i2c_set_clientdata(client, pdata);
>

--
Regards,

Laurent Pinchart