[PATCH v2] drm/r128: fix build for UML

[Sam Ravnborg]

Hi Randy,

On Sun, Oct 10, 2021 at 10:29:55AM -0700, Randy Dunlap wrote:
> Fix a build error on CONFIG_UML, which does not support (provide)
> wbinvd(). UML can use the generic mb() instead.
> 
> ../drivers/gpu/drm/r128/ati_pcigart.c: In function ‘drm_ati_pcigart_init’:
> ../drivers/gpu/drm/r128/ati_pcigart.c:218:2: error: implicit declaration of function ‘wbinvd’ [-Werror=implicit-function-declaration]
>   wbinvd();
>   ^~~~~~
> 
> Fixes: 68f5d3f3b654 ("um: add PCI over virtio emulation driver")
> Signed-off-by: Randy Dunlap <rdunlap at infradead.org>
> Cc: David Airlie <airlied at linux.ie>
> Cc: Daniel Vetter <daniel at ffwll.ch>
> Cc: dri-devel at lists.freedesktop.org
> Cc: Jeff Dike <jdike at addtoit.com>
> Cc: Richard Weinberger <richard at nod.at>
> Cc: Anton Ivanov <anton.ivanov at cambridgegreys.com>
> Cc: linux-um at lists.infradead.org
> ---
> v2: update Fixes: tag (thanks, Johannes)
> 
>  drivers/gpu/drm/r128/ati_pcigart.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- linux-next-20211007.orig/drivers/gpu/drm/r128/ati_pcigart.c
> +++ linux-next-20211007/drivers/gpu/drm/r128/ati_pcigart.c
> @@ -215,7 +215,7 @@ int drm_ati_pcigart_init(struct drm_devi
>  	}
>  	ret = 0;
>  
> -#if defined(__i386__) || defined(__x86_64__)
> +#if (defined(__i386__) || defined(__x86_64__)) && !defined(CONFIG_UML)
>  	wbinvd();
>  #else
>  	mb();

If we look at drivers/video/fbdev/i810/i810_main.h
then it looks like we can replace the above with a simple:
#ifdef CONFIG_X86
	wbinvd();
#else
	mb();
#endif

If you think this would work could you try it out.
It would be nicer with the simpler variant.

Note: I have no clue what wbinvd() does - seems like some x86 assembler
specific thingy.

	Sam