[Intel-gfx] [PATCH 19/19] drm/i915: only enable HWSTAM interrupts on postinstall on ILK+

[Paulo Zanoni]

2014-04-02 8:27 GMT-03:00 Chris Wilson <chris at chris-wilson.co.uk>:
> On Wed, Apr 02, 2014 at 12:23:51PM +0100, Chris Wilson wrote:
>> On Wed, Apr 02, 2014 at 12:21:45PM +0100, Damien Lespiau wrote:
>> > On Tue, Apr 01, 2014 at 03:37:27PM -0300, Paulo Zanoni wrote:
>> > > From: Paulo Zanoni <paulo.r.zanoni at intel.com>
>> > >
>> > > We should only enable interrupts at postinstall.
>> > >
>> > > And now on ILK/SNB/IVB/HSW the irq_preinstall and irq_postinstall
>> > > functions leave the hardware in the same state.
>> > >
>> > > Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
>> >
>> > Orthogonal note to this patch, I'm wondering why we enable any interrupt
>> > reporting in the HW status page, I don't see anywhere we read that
>> > information back? Any idea?
>>
>> Back in the SNB days, interrupts broke without this piece of magic.
>
> To be more precise, iirc, it was a step towards getting coherent
> breadcrumb writes into the HWS. As it turns out, there were more steps
> required. Considering that it can now probably be dropped again? Any
> takers?

I noticed the HWSTAM code looks weird, but I don't really know much
about why it's there, so I decided to not add any regressions. I wrote
this patch a long time ago, and gave up on upstreaming it, but in case
anybody wants, I can send it to the list:
http://cgit.freedesktop.org/~pzanoni/linux/commit/?h=c8-wip&id=7ebe245a2c55379ddc7b36f1fb440215c23f1570
. Look at the commit message, it may be an interesting starting point
if anybody wants to dig on the issue...

> -Chris
>
> --
> Chris Wilson, Intel Open Source Technology Centre



-- 
Paulo Zanoni