Re: [PATCH v2 1/2] of: Create platform devices for OF framebuffers

[Rob Herring <robh@kernel.org>]

On Tue, Apr 19, 2022 at 12:04:04PM +0200, Thomas Zimmermann wrote:
> Create a platform device for each OF-declared framebuffer and have
> offb bind to these devices. Allows for real hot-unplugging and other
> drivers besides offb.
> 
> Originally, offb created framebuffer devices while initializing its
> module by parsing the OF device tree. No actual Linux device was set
> up. This tied OF framebuffers to offb and makes writing other drivers
> for the OF framebuffers complicated. The absence of a Linux device
> further prevented real hot-unplugging. Adding a distinct platform
> device for each OF framebuffer solves both problems. Specifically, a
> DRM driver can now provide graphics output for modern userspace.
> 
> Some of the offb init code is now located in the OF initialization.
> There's now also an implementation of of_platform_default_populate_init(),
> which was missing before. The OF side creates different devices for
> either OF display nodes or BootX displays as they require different
> handling by the driver. The offb drivers picks up each type of device
> and runs the appropriate fbdev initialization.
> 
> Tested with OF display nodes on qemu's ppc64le target.
> 
> v2:
> 	* run PPC code as part of existing initialization (Rob)
> 	* add a few more error warnings (Javier)
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
> ---
>  drivers/of/platform.c      | 88 ++++++++++++++++++++++++++--------
>  drivers/video/fbdev/offb.c | 98 +++++++++++++++++++++++++-------------
>  2 files changed, 132 insertions(+), 54 deletions(-)
> 
> diff --git a/drivers/of/platform.c b/drivers/of/platform.c
> index a16b74f32aa9..738ba2e2838c 100644
> --- a/drivers/of/platform.c
> +++ b/drivers/of/platform.c
> @@ -507,7 +507,6 @@ int of_platform_default_populate(struct device_node *root,
>  }
>  EXPORT_SYMBOL_GPL(of_platform_default_populate);
>  
> -#ifndef CONFIG_PPC
>  static const struct of_device_id reserved_mem_matches[] = {
>  	{ .compatible = "qcom,rmtfs-mem" },
>  	{ .compatible = "qcom,cmd-db" },
> @@ -520,33 +519,81 @@ static const struct of_device_id reserved_mem_matches[] = {
>  
>  static int __init of_platform_default_populate_init(void)
>  {
> -	struct device_node *node;
> -

As both if/else clauses need 'node', I'd keep this declared here.

>  	device_links_supplier_sync_state_pause();
>  
>  	if (!of_have_populated_dt())
>  		return -ENODEV;
>  
> -	/*
> -	 * Handle certain compatibles explicitly, since we don't want to create
> -	 * platform_devices for every node in /reserved-memory with a
> -	 * "compatible",
> -	 */
> -	for_each_matching_node(node, reserved_mem_matches)
> -		of_platform_device_create(node, NULL, NULL);
> +	if (IS_ENABLED(CONFIG_PPC)) {
> +		struct device_node *boot_display = NULL;
> +		struct device_node *node;
> +		struct platform_device *dev;
> +		int ret;
> +
> +		/* Check if we have a MacOS display without a node spec */
> +		if (of_get_property(of_chosen, "linux,bootx-noscreen", NULL)) {
> +			/*
> +			 * The old code tried to work out which node was the MacOS
> +			 * display based on the address. I'm dropping that since the
> +			 * lack of a node spec only happens with old BootX versions
> +			 * (users can update) and with this code, they'll still get
> +			 * a display (just not the palette hacks).
> +			 */
> +			dev = platform_device_alloc("bootx-noscreen", 0);
> +			if (WARN_ON(!dev))
> +				return -ENOMEM;
> +			ret = platform_device_add(dev);
> +			if (WARN_ON(ret)) {
> +				platform_device_put(dev);
> +				return ret;
> +			}
> +		}
>  
> -	node = of_find_node_by_path("/firmware");
> -	if (node) {
> -		of_platform_populate(node, NULL, NULL, NULL);
> -		of_node_put(node);
> -	}
> +		/*
> +		 * For OF framebuffers, first create the device for the boot display,
> +		 * then for the other framebuffers. Only fail for the boot display;
> +		 * ignore errors for the rest.
> +		 */
> +		for_each_node_by_type(node, "display") {
> +			if (!of_get_property(node, "linux,opened", NULL) ||
> +			    !of_get_property(node, "linux,boot-display", NULL))
> +				continue;
> +			dev = of_platform_device_create(node, "of-display", NULL);
> +			if (WARN_ON(!dev))
> +				return -ENOMEM;
> +			boot_display = node;
> +			break;
> +		}
> +		for_each_node_by_type(node, "display") {
> +			if (!of_get_property(node, "linux,opened", NULL) || node == boot_display)
> +				continue;
> +			of_platform_device_create(node, "of-display", NULL);
> +		}
>  
> -	node = of_get_compatible_child(of_chosen, "simple-framebuffer");
> -	of_platform_device_create(node, NULL, NULL);
> -	of_node_put(node);
> +	} else {
> +		struct device_node *node;
> +
> +		/*
> +		 * Handle certain compatibles explicitly, since we don't want to create
> +		 * platform_devices for every node in /reserved-memory with a
> +		 * "compatible",
> +		 */
> +		for_each_matching_node(node, reserved_mem_matches)
> +			of_platform_device_create(node, NULL, NULL);
>  
> -	/* Populate everything else. */
> -	of_platform_default_populate(NULL, NULL, NULL);
> +		node = of_find_node_by_path("/firmware");
> +		if (node) {
> +			of_platform_populate(node, NULL, NULL, NULL);
> +			of_node_put(node);
> +		}
> +
> +		node = of_get_compatible_child(of_chosen, "simple-framebuffer");
> +		of_platform_device_create(node, NULL, NULL);
> +		of_node_put(node);

In v1, you supported "simple-framebuffer" on PPC. Don't we want to allow 
that? Maybe no one cares ATM, but that could change. Either way:

Reviewed-by: Rob Herring <robh@kernel.org>


> +
> +		/* Populate everything else. */
> +		of_platform_default_populate(NULL, NULL, NULL);
> +	}
>  
>  	return 0;
>  }
> @@ -558,7 +605,6 @@ static int __init of_platform_sync_state_init(void)
>  	return 0;
>  }
>  late_initcall_sync(of_platform_sync_state_init);
> -#endif
>  
>  int of_platform_device_destroy(struct device *dev, void *data)
>  {