Message-ID: <63c6f329.050a0220.82479.85d4@mx.google.com>
Date: Tue, 17 Jan 2023 13:12:39 -0600
From: Chris Morgan <macroalpha82@gmail.com>
To: Maxime Ripard <maxime@cerno.tech>
Subject: Re: [PATCH V10 1/4] drm: of: Add drm_of_get_dsi_bus helper function
References: <20230112175358.421975-1-macroalpha82@gmail.com>
 <20230112175358.421975-2-macroalpha82@gmail.com>
 <20230117165819.4rx7aucvyp5e2rj6@houat>
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Cc: devicetree@vger.kernel.org, Chris Morgan <macromorgan@hotmail.com>,
 krzysztof.kozlowski+dt@linaro.org, sam@ravnborg.org,
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On Tue, Jan 17, 2023 at 05:58:19PM +0100, Maxime Ripard wrote:
> Hi,
> 
> On Thu, Jan 12, 2023 at 11:53:55AM -0600, Chris Morgan wrote:
> > From: Chris Morgan <macromorgan@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@hotmail.com>
> > Signed-off-by: Maya Matuszczyk <maccraft123mc@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?
> 

I honestly thought it might be useful, but I can try without it.

> > +		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?
> 

Will do, thank you.

> 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