Re: [PATCH 3.19.y-ckt 027/107] drm/i915: Declare the swizzling unknown for L-shaped configurations

[Kamal Mostafa <kamal@canonical.com>]

On Wed, 2015-08-05 at 14:48 -0700, Kamal Mostafa wrote:
> 3.19.8-ckt5 -stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Chris Wilson <chris@chris-wilson.co.uk>
> 
> commit 19ee835cdb0b5a8eb11a68f25a51b8039d564488 upstream.
> 
> The old style of memory interleaving swizzled upto the end of the
> first even bank of memory,

I notice now that this commit was been reverted and replaced.  I'll drop
this from 3.19-stable and use the replacement 5eb3e5a instead.

5eb3e5a drm/i915: Declare the swizzling unknown for L-shaped configurations
d82c0ba Revert "drm/i915: Declare the swizzling unknown for L-shaped configurations"
19ee835 drm/i915: Declare the swizzling unknown for L-shaped configurations

 -Kamal


>  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 objects.
> 
> v2: Mark the global swizzling as unknown rather than adjust the value
> reported to userspace.
> 
> 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>
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> Signed-off-by: Kamal Mostafa <kamal@canonical.com>
> ---
>  drivers/gpu/drm/i915/i915_gem_tiling.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_tiling.c b/drivers/gpu/drm/i915/i915_gem_tiling.c
> index ffe9072..8ce8c5e 100644
> --- a/drivers/gpu/drm/i915/i915_gem_tiling.c
> +++ b/drivers/gpu/drm/i915/i915_gem_tiling.c
> @@ -183,8 +183,18 @@ i915_gem_detect_bit_6_swizzle(struct drm_device *dev)
>  		if (IS_GEN4(dev)) {
>  			uint32_t ddc2 = I915_READ(DCC2);
>  
> -			if (!(ddc2 & DCC2_MODIFIED_ENHANCED_DISABLE))
> +			if (!(ddc2 & DCC2_MODIFIED_ENHANCED_DISABLE)) {
> +				/* Since the swizzling may vary within an
> +				 * object, we have no idea what the swizzling
> +				 * is for any page in particular. Thus we
> +				 * cannot migrate tiled pages using the GPU,
> +				 * nor can we tell userspace what the exact
> +				 * swizzling is for any object.
> +				 */
>  				dev_priv->quirks |= QUIRK_PIN_SWIZZLED_PAGES;
> +				swizzle_x = I915_BIT_6_SWIZZLE_UNKNOWN;
> +				swizzle_y = I915_BIT_6_SWIZZLE_UNKNOWN;
> +			}
>  		}
>  
>  		if (dcc == 0xffffffff) {