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

[Chris Wilson]

On Wed, Apr 02, 2014 at 11:14:58AM -0300, Paulo Zanoni wrote:
> 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...

Yup, that is very interesting. That may be the minimal piece of HWSTAM
magic we need, and be an interim step to removing HWSTAM entirely.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre