linux-kernel - Re: [PATCH 3/4] drm/sun4i: dsi: Allow binding the host without a panel

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Message-ID: <11bf69b6-9081-7d29-148a-ebc14eef549d@sholland.org>
Date:   Fri, 14 Feb 2020 20:24:50 -0600
From:   Samuel Holland <samuel@...lland.org>
To:     Maxime Ripard <mripard@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH 3/4] drm/sun4i: dsi: Allow binding the host without a
 panel

Maxime,

On 2/11/20 1:28 AM, Samuel Holland wrote:
> Currently, the DSI host blocks binding the display pipeline until the
> panel is available. This unnecessarily prevents other display outpus
> from working, and adds logspam to dmesg when the panel driver is built
> as a module (the component master is unsuccessfully brought up several
> times during boot).
> 
> Flip the dependency, instead requiring the host to be bound before the
> panel is attached. The panel driver provides no functionality outside of
> the display pipeline anyway.
> 
> Since the panel is now probed after the DRM connector, we need a hotplug
> event to turn on the connector after the panel is attached.
> 
> This has the added benefit of fixing panel module removal/insertion.
> Previously, the panel would be turned off when its module was removed.
> But because the connector state was hardcoded, nothing knew to turn the
> panel back on when it was re-attached. Now, with hotplug events
> available, the connector state will follow the panel module state, and
> the panel will be re-enabled properly.
> 
> Fixes: 133add5b5ad4 ("drm/sun4i: Add Allwinner A31 MIPI-DSI controller support")
> Signed-off-by: Samuel Holland <samuel@...lland.org>
> ---
>  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 22 ++++++++++++++++------
>  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.h |  1 +
>  2 files changed, 17 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> index 019fdf4ec274..ef35ce5a9bb0 100644
> --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> @@ -804,7 +804,10 @@ static struct drm_connector_helper_funcs sun6i_dsi_connector_helper_funcs = {
>  static enum drm_connector_status
>  sun6i_dsi_connector_detect(struct drm_connector *connector, bool force)
>  {
> -	return connector_status_connected;
> +	struct sun6i_dsi *dsi = connector_to_sun6i_dsi(connector);
> +
> +	return dsi->panel ? connector_status_connected :
> +			    connector_status_disconnected;
>  }
>  
>  static const struct drm_connector_funcs sun6i_dsi_connector_funcs = {
> @@ -945,10 +948,15 @@ static int sun6i_dsi_attach(struct mipi_dsi_host *host,
>  
>  	if (IS_ERR(panel))
>  		return PTR_ERR(panel);
> +	if (!dsi->drm)
> +		return -EPROBE_DEFER;

There's actually a bug here. If the panel and DSI drivers are loaded in
parallel, sun6i_dsi_attach() can be called after sun6i_dsi_bind() but before
sun4i_framebuffer_init() initializes drm->mode_config.funcs, causing the hotplug
call to crash. This check also needs to consider dsi->drm->registered before
allowing the panel to be added.

I can send a v2 or a follow-up, whichever you prefer.

Thanks,
Samuel

>  	dsi->panel = panel;
>  	dsi->device = device;
>  
> +	drm_panel_attach(dsi->panel, &dsi->connector);
> +	drm_kms_helper_hotplug_event(dsi->drm);
> +
>  	dev_info(host->dev, "Attached device %s\n", device->name);
>  
>  	return 0;
> @@ -958,10 +966,14 @@ static int sun6i_dsi_detach(struct mipi_dsi_host *host,
>  			    struct mipi_dsi_device *device)
>  {
>  	struct sun6i_dsi *dsi = host_to_sun6i_dsi(host);
> +	struct drm_panel *panel = dsi->panel;
>  
>  	dsi->panel = NULL;
>  	dsi->device = NULL;
>  
> +	drm_panel_detach(panel);
> +	drm_kms_helper_hotplug_event(dsi->drm);
> +
>  	return 0;
>  }
>  
> @@ -1026,9 +1038,6 @@ static int sun6i_dsi_bind(struct device *dev, struct device *master,
>  	struct sun6i_dsi *dsi = dev_get_drvdata(dev);
>  	int ret;
>  
> -	if (!dsi->panel)
> -		return -EPROBE_DEFER;
> -
>  	drm_encoder_helper_add(&dsi->encoder,
>  			       &sun6i_dsi_enc_helper_funcs);
>  	ret = drm_encoder_init(drm,
> @@ -1054,7 +1063,8 @@ static int sun6i_dsi_bind(struct device *dev, struct device *master,
>  	}
>  
>  	drm_connector_attach_encoder(&dsi->connector, &dsi->encoder);
> -	drm_panel_attach(dsi->panel, &dsi->connector);
> +
> +	dsi->drm = drm;
>  
>  	return 0;
>  
> @@ -1068,7 +1078,7 @@ static void sun6i_dsi_unbind(struct device *dev, struct device *master,
>  {
>  	struct sun6i_dsi *dsi = dev_get_drvdata(dev);
>  
> -	drm_panel_detach(dsi->panel);
> +	dsi->drm = NULL;
>  }
>  
>  static const struct component_ops sun6i_dsi_ops = {
> diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.h b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.h
> index 61e88ea6044d..c863900ae3b4 100644
> --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.h
> +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.h
> @@ -29,6 +29,7 @@ struct sun6i_dsi {
>  
>  	struct device		*dev;
>  	struct mipi_dsi_device	*device;
> +	struct drm_device	*drm;
>  	struct drm_panel	*panel;
>  };
>  
>