linux-kernel - Re: [PATCH] fbdev: Prevent probing generic drivers if a FB is already registered

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Date:   Thu, 11 Nov 2021 10:54:33 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Sam Ravnborg <sam@...nborg.org>,
        linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Ilya Trukhanov <lahvuun@...il.com>
Subject: Re: [PATCH] fbdev: Prevent probing generic drivers if a FB is
 already registered

On Thu, Nov 11, 2021 at 10:20:53AM +0100, Javier Martinez Canillas wrote:
> The efifb and simplefb drivers just render to a pre-allocated frame buffer
> and rely on the display hardware being initialized before the kernel boots.
> 
> But if another driver already probed correctly and registered a fbdev, the
> generic drivers shouldn't be probed since an actual driver for the display
> hardware is already present.
> 
> Reported-by: Ilya Trukhanov <lahvuun@...il.com>
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>

Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>

Also Cc: stable@...r.kernel.org?

btw time to organize drm-misc commit rights so you can push stuff like
this?
-Daniel

> ---
> 
>  drivers/video/fbdev/efifb.c    | 6 ++++++
>  drivers/video/fbdev/simplefb.c | 6 ++++++
>  2 files changed, 12 insertions(+)
> 
> diff --git drivers/video/fbdev/efifb.c drivers/video/fbdev/efifb.c
> index edca3703b964..76325c07cf0c 100644
> --- drivers/video/fbdev/efifb.c
> +++ drivers/video/fbdev/efifb.c
> @@ -351,6 +351,12 @@ static int efifb_probe(struct platform_device *dev)
>  	char *option = NULL;
>  	efi_memory_desc_t md;
>  
> +	if (num_registered_fb > 0) {
> +		dev_err(&dev->dev,
> +			"efifb: a framebuffer is already registered\n");
> +		return -EINVAL;
> +	}
> +
>  	if (screen_info.orig_video_isVGA != VIDEO_TYPE_EFI || pci_dev_disabled)
>  		return -ENODEV;
>  
> diff --git drivers/video/fbdev/simplefb.c drivers/video/fbdev/simplefb.c
> index 62f0ded70681..55c1f54d7663 100644
> --- drivers/video/fbdev/simplefb.c
> +++ drivers/video/fbdev/simplefb.c
> @@ -407,6 +407,12 @@ static int simplefb_probe(struct platform_device *pdev)
>  	struct simplefb_par *par;
>  	struct resource *mem;
>  
> +	if (num_registered_fb > 0) {
> +		dev_err(&pdev->dev,
> +			"simplefb: a framebuffer is already registered\n");
> +		return -EINVAL;
> +	}
> +
>  	if (fb_get_options("simplefb", NULL))
>  		return -ENODEV;
>  
> -- 
> 2.33.1
> 

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