[Intel-gfx] [PATCH 5/8] drm/i915: Align start for memcpy_from_wc

[Joonas Lahtinen]

Quoting Chris Wilson (2019-12-07 19:01:07)
> The movntqda requires 16-byte alignment for the source pointer. Avoid
> falling back to clflush if the source pointer is misaligned by doing the
> doing a small uncached memcpy to fixup the alignments.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>

<SNIP>

> @@ -1150,19 +1150,30 @@ static u32 *copy_batch(struct drm_i915_gem_object *dst_obj,
>                 return ERR_PTR(ret);
>         }
>  
> +       ptr = dst;

I'd add a newline here as this will propagate to the later branch if WC
map fails.

>         src = ERR_PTR(-ENODEV);
> -       if (src_needs_clflush &&
> -           i915_can_memcpy_from_wc(NULL, offset, 0)) {
> +       if (src_needs_clflush && i915_has_memcpy_from_wc()) {
>                 src = i915_gem_object_pin_map(src_obj, I915_MAP_WC);
>                 if (!IS_ERR(src)) {
> -                       i915_memcpy_from_wc(dst,
> -                                           src + offset,
> -                                           ALIGN(length, 16));
> +                       src += offset;
> +
> +                       if (!IS_ALIGNED(offset, 16)) {
> +                               len = min(ALIGN(offset, 16) - offset, length);
> +
> +                               memcpy(ptr, src, len);
> +
> +                               offset += len;
> +                               length -= len;
> +                               ptr += len;
> +                               src += len;
> +                       }
> +                       GEM_BUG_ON(!IS_ALIGNED((unsigned long)src, 16));
> +
> +                       i915_memcpy_from_wc(ptr, src, ALIGN(length, 16));

Could be a helper function.

Reviewed-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>

Regards, Joonas