linux-kernel - Re: [PATCH 1/2] drm/bridge: Refactor out the panel wrapper from the lvds-encoder bridge.

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Date:   Thu, 27 Apr 2017 10:27:38 -0700
From:   Eric Anholt <eric@...olt.net>
To:     dri-devel@...ts.freedesktop.org
Cc:     linux-kernel@...r.kernel.org,
        Yannick Fertre <yannick.fertre@...com>
Subject: Re: [PATCH 1/2] drm/bridge: Refactor out the panel wrapper from the lvds-encoder bridge.

Eric Anholt <eric@...olt.net> writes:

> Many DRM drivers have common code to make a stub connector
> implementation that wraps a drm_panel.  By wrapping the panel in a DRM
> bridge, all of the connector code (including calls during encoder
> enable/disable) goes away.
>
> Signed-off-by: Eric Anholt <eric@...olt.net>

> +/**
> + * drm_panel_bridge_add - Creates a drm_bridge and drm_connector that
> + * just call the appropriate functions from drm_panel.
> + *
> + * @dev: The struct device of the panel device.  This is used for
> + * registering the drm_bridge.
> + * @panel: The drm_panel being wrapped.  Must be non-NULL.
> + * @connector_type: The DRM_MODE_CONNECTOR_* for the connector to be
> + * created.
> + *
> + * For drivers converting from directly using drm_panel: The expected
> + * usage pattern is that during either encoder module probe or DSI
> + * host attach, a drm_panel will be looked up through
> + * drm_of_find_panel_or_bridge().  drm_panel_bridge_add() is used to
> + * wrap that panel in the new bridge, and the result can then be
> + * passed to drm_bridge_attach().  The drm_panel_prepare() and related
> + * functions can be dropped from the encoder driver (they're now
> + * called by the KMS helpers before calling into the encoder), along
> + * with connector creation.
> + */
> +struct drm_bridge *drm_panel_bridge_add(struct device *dev,
> +					struct drm_panel *panel,
> +					u32 connector_type)
> +{
> +	struct panel_bridge *panel_bridge =
> +		devm_kzalloc(dev, sizeof(*panel_bridge), GFP_KERNEL);
> +	int ret;
> +
> +	if (!dev || !panel)
> +		return ERR_PTR(EINVAL);
> +
> +	panel_bridge->dev = dev;
> +	panel_bridge->connector_type = connector_type;
> +	panel_bridge->panel = panel;
> +
> +	panel_bridge->bridge.funcs = &panel_bridge_bridge_funcs;
> +	panel_bridge->bridge.of_node = dev->of_node;
> +
> +	ret = drm_bridge_add(&panel_bridge->bridge);
> +	if (ret)
> +		return ERR_PTR(ret);
> +
> +	return &panel_bridge->bridge;
> +}
> +EXPORT_SYMBOL(drm_panel_bridge_add);
> +
> +void drm_panel_bridge_remove(struct device *dev, struct drm_bridge *bridge)
> +{
> +	drm_bridge_remove(bridge);
> +	devm_kfree(dev, bridge);
> +}
> +EXPORT_SYMBOL(drm_panel_bridge_remove);

Working with this interface in another driver, I want to drop the
"struct device" argument, since we can get the struct device from
panel->dev.  It keeps the user of the driver from needing to keep track
of the panel/device it needs to hand to drm_panel_bridge_remove().

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