Re: [Intel-gfx] [PATCH 2/5] drm/i915: preserve swizzle settings if necessary v3

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On 06/11/2014 08:41 AM, Jesse Barnes wrote:
On Wed, 11 Jun 2014 17:39:29 +0200
Daniel Vetter <daniel@xxxxxxxx> wrote:

On Wed, Jun 11, 2014 at 5:13 PM, Jesse Barnes <jbarnes@xxxxxxxxxxxxxxxx> 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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