[PATCH V10 1/4] drm: of: Add drm_of_get_dsi_bus helper function

[Maxime Ripard]

Hi,

On Thu, Jan 12, 2023 at 11:53:55AM -0600, Chris Morgan wrote:
> From: Chris Morgan <macromorgan at hotmail.com>
> 
> Add helper function to find DSI host for devices where DSI panel is not
> a minor of a DSI bus (such as the Samsung AMS495QA01 panel or the
> official Raspberry Pi touchscreen display).
> 
> Signed-off-by: Chris Morgan <macromorgan at hotmail.com>
> Signed-off-by: Maya Matuszczyk <maccraft123mc at gmail.com>
> ---
>  drivers/gpu/drm/drm_of.c | 70 ++++++++++++++++++++++++++++++++++++++++
>  include/drm/drm_of.h     | 10 ++++++
>  2 files changed, 80 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_of.c b/drivers/gpu/drm/drm_of.c
> index 7bbcb999bb75..6c2c97a716fe 100644
> --- a/drivers/gpu/drm/drm_of.c
> +++ b/drivers/gpu/drm/drm_of.c
> @@ -10,6 +10,7 @@
>  #include <drm/drm_crtc.h>
>  #include <drm/drm_device.h>
>  #include <drm/drm_encoder.h>
> +#include <drm/drm_mipi_dsi.h>
>  #include <drm/drm_of.h>
>  #include <drm/drm_panel.h>
>  
> @@ -493,3 +494,72 @@ int drm_of_get_data_lanes_count_ep(const struct device_node *port,
>  	return ret;
>  }
>  EXPORT_SYMBOL_GPL(drm_of_get_data_lanes_count_ep);
> +
> +#if IS_ENABLED(CONFIG_DRM_MIPI_DSI)
> +
> +/**
> + * drm_of_get_dsi_bus - find the DSI bus for a given device
> + * @dev: parent device of display (SPI, I2C)
> + * @info: DSI device info to be updated with DSI node. This is optional
> + * and if not needed can be NULL.
> + *
> + * Gets parent DSI bus for a DSI device controlled through a bus other
> + * than MIPI-DCS (SPI, I2C, etc.) using the Device Tree.
> + *
> + * Returns pointer to mipi_dsi_host if successful, -EINVAL if the
> + * request is unsupported, -EPROBE_DEFER if the DSI host is found but
> + * not available, or -ENODEV otherwise.
> + */
> +struct mipi_dsi_host *drm_of_get_dsi_bus(struct device *dev,
> +					 struct mipi_dsi_device_info *info)
> +{
> +	struct mipi_dsi_host *dsi_host;
> +	struct device_node *endpoint, *dsi_host_node;
> +
> +	/*
> +	 * Get first endpoint child from device.
> +	 */
> +	endpoint = of_graph_get_next_endpoint(dev->of_node, NULL);
> +	if (!endpoint)
> +		return ERR_PTR(-ENODEV);
> +
> +	/*
> +	 * Follow the first endpoint to get the DSI host node.
> +	 */
> +	dsi_host_node = of_graph_get_remote_port_parent(endpoint);
> +	if (!dsi_host_node)
> +		goto error;
> +
> +	/*
> +	 * Get the DSI host from the DSI host node. If we get an error
> +	 * or the return is null assume we're not ready to probe just
> +	 * yet. Release the DSI host node since we're done with it.
> +	 */
> +	dsi_host = of_find_mipi_dsi_host_by_node(dsi_host_node);
> +	of_node_put(dsi_host_node);
> +	if (IS_ERR_OR_NULL(dsi_host)) {
> +		of_node_put(endpoint);
> +		return ERR_PTR(-EPROBE_DEFER);
> +	}
> +
> +	/*
> +	 * Set the node of the mipi_dsi_device_info to the correct node
> +	 * and then release the endpoint node since we're done with it.
> +	 * since this is optional, check if the info is NULL first.
> +	 */
> +	if (info) {
> +		info->node = of_graph_get_remote_port(endpoint);

it looks to me that the info->node is actually the DSI device OF node,
not its host port. Which begs the question, why should we even return it
there, since there's a pretty big chance that dev->of.node ==
info->node, and you obviously don't care about the channel and type fields.

I've had a look and node of the current users of
mipi_dsi_device_register_full actually register a mipi_dsi_device_info
with a node pointer set to !NULL, including the driver in this series.

So, why do we care about the device info at all?

> +		if (IS_ERR_OR_NULL(info->node))

of_graph_get_remote_port doesn't return an error pointer.

> --- a/include/drm/drm_of.h
> +++ b/include/drm/drm_of.h
> @@ -15,6 +15,8 @@ struct drm_encoder;
>  struct drm_panel;
>  struct drm_bridge;
>  struct device_node;
> +struct mipi_dsi_device_info;
> +struct mipi_dsi_host;
>  
>  /**
>   * enum drm_lvds_dual_link_pixels - Pixel order of an LVDS dual-link connection
> @@ -56,6 +58,8 @@ int drm_of_get_data_lanes_count_ep(const struct device_node *port,
>  				   int port_reg, int reg,
>  				   const unsigned int min,
>  				   const unsigned int max);
> +struct mipi_dsi_host *drm_of_get_dsi_bus(struct device *dev,
> +					 struct mipi_dsi_device_info *info);
>  #else
>  static inline uint32_t drm_of_crtc_port_mask(struct drm_device *dev,
>  					  struct device_node *port)
> @@ -127,6 +131,12 @@ drm_of_get_data_lanes_count_ep(const struct device_node *port,
>  {
>  	return -EINVAL;
>  }
> +static inline struct
> +mipi_dsi_host *drm_of_get_dsi_bus(struct device *dev,
> +					 struct mipi_dsi_device_info *info)
> +{
> +	return ERR_PTR(-EINVAL);
> +}
>  #endif

So it looks to me that if CONFIG_OF is defined, we'll define an external
symbol declared for drm_of_get_dsi_bus, but that function will only be
compiled if CONFIG_DRM_MIPI_DSI is enabled.

What happens if we have CONFIG_OF but not CONFIG_DRM_MIPI_DSI?

If think you need to have here something like:

#ifdef IS_ENABLED(CONFIG_OF) && IS_ENABLED(CONFIG_DRM_MIPI_DSI)
struct mipi_dsi_host *drm_of_get_dsi_bus(struct device *dev,
       					 struct mipi_dsi_device_info *info);
#else
static inline struct
mipi_dsi_host *drm_of_get_dsi_bus(struct device *dev,
				  struct mipi_dsi_device_info *info)
{
	return ERR_PTR(-EINVAL);
}
#endif

Maxime
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