Unverified Commit fb561bf9 authored Nov 11, 2021 by Javier Martinez Canillas

fbdev: Prevent probing generic drivers if a FB is already registered

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.

This is more likely to occur after commit d391c582 ("drivers/firmware:
move x86 Generic System Framebuffers support") since the "efi-framebuffer"
and "simple-framebuffer" platform devices are registered at a later time.

Link: https://lore.kernel.org/r/20211110200253.rfudkt3edbd3nsyj@lahvuun/

Fixes: d391c582 ("drivers/firmware: move x86 Generic System Framebuffers support")
Reported-by: Ilya Trukhanov <lahvuun@gmail.com>
Cc: <stable@vger.kernel.org> # 5.15.x
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Tested-by: Ilya Trukhanov <lahvuun@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211111115757.1351045-1-javierm@redhat.com

parent 963d0b35

drivers/video/fbdev/efifb.c

+11 −0

Original line number	Diff line number	Diff line
		@@ -351,6 +351,17 @@ static int efifb_probe(struct platform_device *dev)
		char *option = NULL;
		efi_memory_desc_t md;

		/*
		* Generic drivers must not be registered if a framebuffer exists.
		* If a native driver was probed, the display hardware was already
		* taken and attempting to use the system framebuffer is dangerous.
		*/
		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;

+11 −0

Original line number	Diff line number	Diff line
		@@ -407,6 +407,17 @@ static int simplefb_probe(struct platform_device *pdev)
		struct simplefb_par *par;
		struct resource *mem;

		/*
		* Generic drivers must not be registered if a framebuffer exists.
		* If a native driver was probed, the display hardware was already
		* taken and attempting to use the system framebuffer is dangerous.
		*/
		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;