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

From: Jani Nikula <jani.nikula@linux.intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>, intel-gfx@lists.freedesktop.org
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>, stable@vger.kernel.org
Subject: Re: [Intel-gfx] [PATCH] drm/i915: Declare the swizzling unknown for L-shaped configurations
Date: Mon, 29 Jun 2015 15:25:02 +0300	[thread overview]
Message-ID: <878ub2ya5d.fsf@intel.com> (raw)
In-Reply-To: <20150628125254.GK14226@nuc-i3427.alporthouse.com>

On Sun, 28 Jun 2015, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> 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.

Are you planning on sending an updated patch, or shall I merge this one?

BR,
Jani.

> -Chris
>
> -- 
> Chris Wilson, Intel Open Source Technology Centre
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> Intel-gfx@lists.freedesktop.org
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-- 
Jani Nikula, Intel Open Source Technology Center