[Intel-gfx] [PATCH 2/5] drm/i915: preserve swizzle settings if necessary v3
Steve Aarnio
steve.j.aarnio at linux.intel.com
Fri Jun 27 18:15:25 CEST 2014
On 06/11/2014 08:41 AM, Jesse Barnes wrote:
> On Wed, 11 Jun 2014 17:39:29 +0200
> Daniel Vetter <daniel at ffwll.ch> wrote:
>
>> On Wed, Jun 11, 2014 at 5:13 PM, Jesse Barnes <jbarnes at virtuousgeek.org> wrote:
>>>> - If you have a machine which uses tiled framebuffers and enables
>>>> swizzling in the BIOS your code will a) drop the swizzle setup in
>>>> gem_init_hw, breaking resume b) not set the swizzle settings correctly
>>>> in swizzle_detect, breaking swap in/out and pwrite/pread. Not sure such
>>>> a machine exists, but still.
>>>
>>> This would affect krh's MBA, which is why I wanted testing here...
>>> anyway I'll spin a new one and ask krh to test again.
>>
>> Hm, I've thought the issue with the MBA is that it used tiled fbs, but
>> non-swizzled. And then a mess ensued when we've enabled it. But yeah,
>> unfortunately with the new logic we need to retest :(
>
> Ah yeah I think you're right, either way, need more testing.
>
> Maybe we should have just gone with the first patch to never enable
> swizzling based on Art's assertion that it didn't matter.
>
I hate to jump into the middle of a conversation that may or may not be related
to a patch I just posted... but...
There was a very long internal discussion that the Windows guys had with H/W.
For Gen8+ H/W recommends disabling CSX swizzle. Technically, BDW still supports
it, but there is a bug _somewhere_ that makes it problematic. In any case it
goes away for sure with Gen9+, so disabling on Gen8 doesn't hurt.
According to the other discussion, the H/W guys say that enabling actually hurts
performance slightly, and the driver should leave the swizzle decisions to the
memory controller.
Stevo
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