[Intel-gfx] [PATCH 3/7] drm/i915/guc: Add GuC <-> kernel time stamp translation information

[Teres Alexis, Alan Previn]

Sounds good - thanks. (ignore the "doing the opposite" comment).

Reviewed-by: Alan Previn <alan.previn.teres.alexis at intel.com>

On Mon, 2022-08-08 at 11:43 -0700, Harrison, John C wrote:
> On 8/4/2022 17:40, Teres Alexis, Alan Previn wrote:
> > I have a question on below code. Everything else looked good.
> > Will r-b as soon as we can close on below question
> > ...alan
> > 
> > 
> > On Wed, 2022-07-27 at 19:20 -0700, John.C.Harrison at Intel.com wrote:
> > > From: John Harrison <John.C.Harrison at Intel.com>
> > > 
> > > It is useful to be able to match GuC events to kernel events when
> > > looking at the GuC log. That requires being able to convert GuC
> > > timestamps to kernel time. So, when dumping error captures and/or GuC
> > > logs, include a stamp in both time zones plus the clock frequency.
> > > 
> > > Signed-off-by: John Harrison <John.C.Harrison at Intel.com>
> > > --- a/drivers/gpu/drm/i915/i915_gpu_error.c
> > > +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
> > > @@ -1675,6 +1678,13 @@ gt_record_uc(struct intel_gt_coredump *gt,
> > >   	 */
> > >   	error_uc->guc_fw.path = kstrdup(uc->guc.fw.path, ALLOW_FAIL);
> > >   	error_uc->huc_fw.path = kstrdup(uc->huc.fw.path, ALLOW_FAIL);
> > > +
> > > +	/*
> > > +	 * Save the GuC log and include a timestamp reference for converting the
> > > +	 * log times to system times (in conjunction with the error->boottime and
> > > +	 * gt->clock_frequency fields saved elsewhere).
> > > +	 */
> > > +	error_uc->timestamp = intel_uncore_read(gt->_gt->uncore, GUCPMTIMESTAMP);
> > Alan:this register is in the GUC-SHIM domain and so unless i am mistaken u might need to ensure we hold a wakeref so
> > that are getting a live value of the real timestamp register that this register is mirror-ing and not a stale snapshot.
> > Or was this already done farther up the stack? Or are we doing the opposite - in which case we should ensure we drop al
> >   wakeref prior to this point. (which i am not sure is a reliable method since we wouldnt know what GuC ref was at).
> The intel_uncore_read() does a forcewake acquire implicitly.
> 
> Not sure what you mean about dropping all wakerefs prior to this point?
> 
> John.
> 
> > >   	error_uc->guc_log = create_vma_coredump(gt->_gt, uc->guc.log.vma,
> > >   						"GuC log buffer", compress);
> > >