[PATCH] drm: support gpu aliases defined in DT data

[Daniel Vetter]

On Thu, Jan 17, 2019 at 01:19:18PM +0200, Tomi Valkeinen wrote:
> The DRM device minor numbers are allocated according to the registration
> order. This causes confusion in cases where the registration order can
> change, or when, say, a modesetting capable device is preferred to be
> card0, and a rendering device is preferred to be card1.
> 
> This patch adds similar functionality that is used in some other
> subsystems, where device minor numbers can be defined in DT bindings'
> aliases node.

What other subsystem? I thought that minor numbers shouldn't be made uapi,
and that udev or similar is supposed to give you stable names ... Is that
not the case on SoC?

If we go with this I think we need a few acks from soc-tree people that
this is a reasonable idea which should be copied around.
-Daniel


> For example, this sets the DRM device minor number to 1 for the 'dss'
> device.
> 
> aliases {
> 	gpu1 = &dss;
> };
> 
> The logic on how to pick the minor number is:
> 
> - if there's a DT gpu alias for the device, use that
> - else, if there are any gpu aliases, pick a minor number that is higher
>   than any of the aliases.
> - else, use the full range of possible numbers
> 
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen at ti.com>
> ---
>  drivers/gpu/drm/drm_drv.c | 31 +++++++++++++++++++++++++++++--
>  1 file changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index a5fe91b8c3c9..f536a2760293 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -110,6 +110,8 @@ static int drm_minor_alloc(struct drm_device *dev, unsigned int type)
>  	struct drm_minor *minor;
>  	unsigned long flags;
>  	int r;
> +	int min_id, max_id;
> +	bool of_id_found = false;
>  
>  	minor = kzalloc(sizeof(*minor), GFP_KERNEL);
>  	if (!minor)
> @@ -118,12 +120,37 @@ static int drm_minor_alloc(struct drm_device *dev, unsigned int type)
>  	minor->type = type;
>  	minor->dev = dev;
>  
> +	min_id = 64 * type;
> +	max_id = 64 * (type + 1);
> +
> +	if (dev->dev && dev->dev->of_node) {
> +		int id;
> +
> +		id = of_alias_get_id(dev->dev->of_node, "gpu");
> +
> +		if (id >= 0) {
> +			min_id = 64 * type + id;
> +			max_id = 64 * type + id + 1;
> +
> +			of_id_found = true;
> +		}
> +	}
> +
> +	if (!of_id_found) {
> +		int id;
> +
> +		id = of_alias_get_highest_id("gpu");
> +
> +		if (id >= 0)
> +			min_id = id + 1;
> +	}
> +
>  	idr_preload(GFP_KERNEL);
>  	spin_lock_irqsave(&drm_minor_lock, flags);
>  	r = idr_alloc(&drm_minors_idr,
>  		      NULL,
> -		      64 * type,
> -		      64 * (type + 1),
> +		      min_id,
> +		      max_id,
>  		      GFP_NOWAIT);
>  	spin_unlock_irqrestore(&drm_minor_lock, flags);
>  	idr_preload_end();
> -- 
> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
> Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch