[Intel-gfx] [PATCH] drm/i915/gem: stop using PAGE_KERNEL_IO

[Daniel Vetter]

On Wed, Oct 20, 2021 at 02:06:25AM -0700, Lucas De Marchi wrote:
> PAGE_KERNEL_IO is only defined for x86 and is the same as PAGE_KERNEL.
> Use the latter since that is also available on other archs, which should
> help us getting i915 there.
> 
> This is the same that was done done in commit 80c33624e472 ("io-mapping:
> Fixup for different names of writecombine"). Later the commit
> 80c33624e472 ("io-mapping: Fixup for different names of writecombine")
> added a "Fixes" tag to the first one, but that is actually fixing a
> separate issue:  the different names for pgprot_writecombine().
> 
> Fast-forward today, it seems the only 2 archs that define
> pgprot_noncached_wc() are microblaze and powerpc. Microblaze has the
> same definition for pgprot_writecombine() since commit
> 97ccedd793ac ("microblaze: Provide pgprot_device/writecombine macros for
> nommu"). Powerpc has 3 variants and all of them have the same behavior
> for pgprot_writecombine() and pgprot_noncached_wc(). From the commit message
> and linked issue, the fallback was needed for arm, but apparently today
> all the variants there also have pgprot_writecombine().
> 
> So, just use PAGE_KERNEL, and just use pgprot_writecombine().
> 
> Signed-off-by: Lucas De Marchi <lucas.demarchi at intel.com>

I think a bit more history on PAGE_KERNEL_IO is useful to add. It was
added in be43d72835ba ("x86: add _PAGE_IOMAP pte flag for IO mappings").
The one and only user was lost in f955371ca9d3 ("x86: remove the
Xen-specific _PAGE_IOMAP PTE flag"), therefore it's safe to do this.

With that added Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

Also if you're motivated, maybe delete PAGE_KERNEL_IO across the tree and
get x86 maintainers to merge the entire series?
-Daniel


> ---
>  drivers/gpu/drm/i915/gem/i915_gem_pages.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_pages.c b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> index 8eb1c3a6fc9c..68fe1837ef54 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> @@ -289,7 +289,7 @@ static void *i915_gem_object_map_page(struct drm_i915_gem_object *obj,
>  		pgprot = PAGE_KERNEL;
>  		break;
>  	case I915_MAP_WC:
> -		pgprot = pgprot_writecombine(PAGE_KERNEL_IO);
> +		pgprot = pgprot_writecombine(PAGE_KERNEL);
>  		break;
>  	}
>  
> @@ -333,7 +333,7 @@ static void *i915_gem_object_map_pfn(struct drm_i915_gem_object *obj,
>  	i = 0;
>  	for_each_sgt_daddr(addr, iter, obj->mm.pages)
>  		pfns[i++] = (iomap + addr) >> PAGE_SHIFT;
> -	vaddr = vmap_pfn(pfns, n_pfn, pgprot_writecombine(PAGE_KERNEL_IO));
> +	vaddr = vmap_pfn(pfns, n_pfn, pgprot_writecombine(PAGE_KERNEL));
>  	if (pfns != stack)
>  		kvfree(pfns);
>  
> -- 
> 2.33.1
> 

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