Re: [PATCH v6 2/6] drm: sun4i: dsi: Add component only once DSI device attached

[Maxime Ripard <maxime@cerno.tech>]

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On Fri, Dec 10, 2021 at 04:47:07PM +0530, Jagan Teki wrote:
> Having component_add for running all drm bind callbacks returns
> error or unbound due to chain of DSI devices connected across
> bridge topology on a display pipeline.

I'm not sure what that means?

> In a typical bridge oriented display pipeline where the host is
> connected to the bridge converter and that indeed connected to
> a panel.
> 
> DRM => SUN6I DSI Host => Chipone ICN6211 => BananaPi Panel
> 
> The bridge converter is looking for a panel to probe first and
> then attach the host. The host attach is looking for a bridge
> converter to probe and preserve bridge pointer, at this movement

                                                          ^ moment ?

> the host is trying to bind the all callbacks and one of the bind
> callback in the DSI host is trying to find the bridge using the
> bridge pointer in sun6i_dsi_attach call.
> 
> chipone_probe().start
>     drm_of_find_panel_or_bridge
>         mipi_dsi_attach
>              sun6i_dsi_attach
>                  drm_of_find_panel_or_bridge
> chipone_probe().done
> 
> sun6i_dsi_probe().start
>     mipi_dsi_host_register
>         component_add
> sun6i_dsi_probe().done
> 
> However, the movement when panel defers the probe, will make the
> bridge converter defer the host attach call which eventually found
> a NULL bridge pointer during DSI component bind callback.
> 
> So, in order to prevent this scenario of binding invalid bridge,
> wait for DSI devices on the pipeline to probe first and start the
> binding process by moving component_add in host probe to attach call.
> 
> chipone_probe().start
>     drm_of_find_panel_or_bridge
>         mipi_dsi_attach
>              sun6i_dsi_attach
>                  drm_of_find_panel_or_bridge
>       		      component_add
> chipone_probe().done
> 
> sun6i_dsi_probe().start
>     mipi_dsi_host_register
> sun6i_dsi_probe().done
> 
> Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
> ---
> Changes for v6:
> - none
> Changes for v5:
> - new patch
> 
>  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 120 +++++++++++++------------
>  1 file changed, 61 insertions(+), 59 deletions(-)
> 
> diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> index 4bdcce8f1d84..9cf91dcac3f2 100644
> --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> @@ -959,11 +959,63 @@ static int sun6i_dsi_dcs_read(struct sun6i_dsi *dsi,
>  	return 1;
>  }
>  
> +static int sun6i_dsi_bind(struct device *dev, struct device *master,
> +			 void *data)
> +{
> +	struct drm_device *drm = data;
> +	struct sun6i_dsi *dsi = dev_get_drvdata(dev);
> +	int ret;
> +
> +	drm_encoder_helper_add(&dsi->encoder,
> +			       &sun6i_dsi_enc_helper_funcs);
> +	ret = drm_simple_encoder_init(drm, &dsi->encoder,
> +				      DRM_MODE_ENCODER_DSI);
> +	if (ret) {
> +		dev_err(dsi->dev, "Couldn't initialise the DSI encoder\n");
> +		return ret;
> +	}
> +	dsi->encoder.possible_crtcs = BIT(0);
> +
> +	drm_connector_helper_add(&dsi->connector,
> +				 &sun6i_dsi_connector_helper_funcs);
> +	ret = drm_connector_init(drm, &dsi->connector,
> +				 &sun6i_dsi_connector_funcs,
> +				 DRM_MODE_CONNECTOR_DSI);
> +	if (ret) {
> +		dev_err(dsi->dev,
> +			"Couldn't initialise the DSI connector\n");
> +		goto err_cleanup_connector;
> +	}
> +
> +	drm_connector_attach_encoder(&dsi->connector, &dsi->encoder);
> +
> +	return 0;
> +
> +err_cleanup_connector:
> +	drm_encoder_cleanup(&dsi->encoder);
> +	return ret;
> +}
> +
> +static void sun6i_dsi_unbind(struct device *dev, struct device *master,
> +			    void *data)
> +{
> +	struct sun6i_dsi *dsi = dev_get_drvdata(dev);
> +
> +	drm_encoder_cleanup(&dsi->encoder);
> +}
> +
> +static const struct component_ops sun6i_dsi_ops = {
> +	.bind	= sun6i_dsi_bind,
> +	.unbind	= sun6i_dsi_unbind,
> +};

Just use a forward declaration there, it will make the patch more
straightforward.

Maxime

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