[PATCH v2 07/11] video/aperture: Disable and unregister sysfb devices via aperture helpers

[Samuel Čavoj]

Hi,

> diff --git a/drivers/video/aperture.c b/drivers/video/aperture.c
> index f42a0d8bc211..101e13c2cf41 100644
> --- a/drivers/video/aperture.c
> +++ b/drivers/video/aperture.c
> @@ -8,6 +8,7 @@
>  #include <linux/pci.h>
>  #include <linux/platform_device.h>
>  #include <linux/slab.h>
> +#include <linux/sysfb.h>
>  #include <linux/types.h>
>  #include <linux/vgaarb.h>
> 
> @@ -286,7 +287,20 @@ int 
> aperture_remove_conflicting_devices(resource_size_t base, 
> resource_size_t si
>  #if IS_REACHABLE(CONFIG_FB)
>  	struct apertures_struct *a;
>  	int ret;
> +#endif
> +
> +	/*
> +	 * If a driver asked to unregister a platform device registered by
> +	 * sysfb, then can be assumed that this is a driver for a display
> +	 * that is set up by the system firmware and has a generic driver.
> +	 *
> +	 * Drivers for devices that don't have a generic driver will never
> +	 * ask for this, so let's assume that a real driver for the display
> +	 * was already probed and prevent sysfb to register devices later.
> +	 */
> +	sysfb_disable();

This call to sysfb_disable() has been causing trouble with regard to
VFIO. VFIO has been calling aperture_remove_conflicting_pci_devices to
get rid of any console drivers (d173780620792c) using the device in
question, but now even unrelated drivers are getting killed. Example
situation:

Machine has two GPUs and uses efifb for the console. Efifb registers
with the aperture system the efi framebuffer region, which is covered
by a BAR resource of GPU 1. VFIO grabs GPU 2 and calls
aperture_remove_conflicting_pci_devices(GPU 2). GPU 2 has no overlap
with the efifb on GPU1 but the efifb is killed regardless due to
the unconditional call to sysfb_disable(). The console switches
to dummy and locks up from the user perspective.
This seems unnecessary, as the device is unrelated.

I do not quite understand the comment justifying the call.

Some discussions with workarounds:
https://old.reddit.com/r/VFIO/comments/11qei4t/framebuffer_doesnt_work_anymore_after_passthrough/
https://bbs.archlinux.org/viewtopic.php?id=280512


Thanks,
Samuel