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

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Date:   Tue, 2 Jul 2019 18:20:11 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Rob Clark <robdclark@...il.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        freedreno@...ts.freedesktop.org, aarch64-laptops@...ts.linaro.org,
        linux-clk@...r.kernel.org, linux-pm@...r.kernel.org,
        Rob Clark <robdclark@...omium.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] drm/bridge: ti-sn65dsi86: support booloader enabled
 display

Hi Rob,

Thank you for the patch.

On Sun, Jun 30, 2019 at 08:01:43AM -0700, Rob Clark wrote:
> From: Rob Clark <robdclark@...omium.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@...omium.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