Re: [PATCH v2] drm/i915: Declare the swizzling unknown for L-shaped configurations

From: Daniel Vetter <daniel@ffwll.ch>
To: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>,
	intel-gfx@lists.freedesktop.org, stable@vger.kernel.org
Subject: Re: [PATCH v2] drm/i915: Declare the swizzling unknown for L-shaped configurations
Date: Thu, 9 Jul 2015 09:37:08 +0200	[thread overview]
Message-ID: <20150709073708.GC21858@phenom.ffwll.local> (raw)
In-Reply-To: <1435582879-32012-1-git-send-email-chris@chris-wilson.co.uk>

On Mon, Jun 29, 2015 at 02:01:19PM +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 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>
> Cc: stable@vger.kernel.org

Applied to -fixes, thanks.
-Daniel

> ---
>  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 d16585f788ea..a0d98f0abc71 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) {
> -- 
> 2.1.4
> 

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