Re: [PATCH] drm/i915: Declare the swizzling unknown for L-shaped configurations

[Chris Wilson <chris@chris-wilson.co.uk>]

On Sun, Jun 28, 2015 at 09:19:26AM +0100, Chris Wilson wrote:
> The old style of memory interleaving swizzled upto the end of the
> first even bank of memory, and then used the remainder as unswizzled on
> the unpaired bank - i.e. swizzling is not constant for all memory. This
> causes problems when we try to migrate memory and so the kernel prevents
> migration at all when we detect L-shaped inconsistent swizzling.
> However, this issue also extends to userspace who try to manually detile
> into memory as the swizzling for an individual page is unknown (it
> depends on its physical address only known to the kernel), userspace
> cannot correctly swizzle.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91105
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: stable@vger.kernel.org
> ---
>  drivers/gpu/drm/i915/i915_gem_tiling.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_tiling.c b/drivers/gpu/drm/i915/i915_gem_tiling.c
> index d16585f788ea..ff96ae9b77bc 100644
> --- a/drivers/gpu/drm/i915/i915_gem_tiling.c
> +++ b/drivers/gpu/drm/i915/i915_gem_tiling.c
> @@ -447,7 +447,10 @@ i915_gem_get_tiling(struct drm_device *dev, void *data,
>  	}
>  
>  	/* Hide bit 17 from the user -- see comment in i915_gem_set_tiling */
> -	args->phys_swizzle_mode = args->swizzle_mode;
> +	if (dev_priv->quirks & QUIRK_PIN_SWIZZLED_PAGES)
> +		args->phys_swizzle_mode = I915_BIT_6_SWIZZLE_UNKNOWN;
> +	else
> +		args->phys_swizzle_mode = args->swizzle_mode;

It may be better to store the dev_priv->mm.bit_6_swizzle_[xy] as UNKNOWN
for L-shaped memory. I think that would be more correct.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre