Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> writes:
> On Wed, Jan 28, 2015 at 03:28:56PM +0200, Mika Kuoppala wrote:
>> Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
>>
>> > On Wed, Jan 28, 2015 at 02:43:25PM +0200, Mika Kuoppala wrote:
>> >> commit 05a2fb157e44a53c79133805d30eaada43911941
>> >> Author: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
>> >> Date: Mon Jan 19 16:20:43 2015 +0200
>> >>
>> >> drm/i915: Consolidate forcewake code
>> >>
>> >> introduced domain handling where each domain has it's own posting
>> >> read registers. This changed the forcewake sequence on 'put' side when
>> >> there is multiple domains as there would be extra read between the domain
>> >> puts. Any posting read should be enough to flush all the changes.
>> >>
>> >> Do a posting read only once, at the end of the sequence and for
>> >> the first domain. Like it was before.
>> >>
>> >> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
>> >> Signed-off-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxx>
>> >
>> > fwiw, I would argue that the posting read in _get() is superfluous as we
>> > will serialise the fw with not only the ack, but any subsequent mmio.
>> >
>> > On the _put() side we do want to flush the write so that the hw can
>> > power down as early as possible. So just kill the posting read from _get
>> > and otherwise drop the patch. :)
>>
>> Yes, both put/get patches should be dropped. I posted a patch removing
>> the posting read on get side and with your explanations in commit message.
>>
>> This all starts to make so much sense that some gen is bound to break ;)
>
> IIRC the posting read from same cache line actually fixed real bugs. So
> I'm a bit worried about dropping them. But I suppose it's possible only
> the _put side was important for those bugs.
I found these:
commit 6af2d180f82151cf3d58952e35a4f96e45bc453a
Author: Daniel Vetter <daniel.vetter@xxxxxxxx>
Date: Thu Jul 26 16:24:50 2012 +0200
drm/i915: fix forcewake related hangs on snb
commit 8dee3eea3ccd3b6c00a8d3a08dd715d6adf737dd
Author: Ben Widawsky <ben@xxxxxxxxxxxx>
Date: Sat Sep 1 22:59:50 2012 -0700
drm/i915: Never read FORCEWAKE
https://bugs.freedesktop.org/show_bug.cgi?id=51738
https://bugs.freedesktop.org/show_bug.cgi?id=52424
The snb here seems to survive gem_dummy_reloc_loop and
gem_ring_sync_loop in here with the get side posting removed.
-Mika
>
> --
> Ville Syrjälä
> Intel OTC
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