Re: [Intel-gfx] [PATCH 1/2] drm/i915/pmu: Use functions common with sysfs to read actual freq

["Dixit, Ashutosh" <ashutosh.dixit@intel.com>]

On Thu, 09 Mar 2023 01:20:09 -0800, Tvrtko Ursulin wrote:
>

Hi Tvrtko,

> On 09/03/2023 03:46, Ashutosh Dixit wrote:
> > Expose intel_rps_read_actual_frequency_fw to read the actual freq without
> > taking forcewake for use by PMU. The code is refactored to use a common set
> > of functions across sysfs and PMU. Using common functions with sysfs in PMU
> > solves the issues of missing support for MTL and missing support for older
> > generations (prior to Gen6). It also future proofs the PMU where sometimes
> > code has been updated for sysfs and PMU has been missed.
> >
> > Fixes: 22009b6dad66 ("drm/i915/mtl: Modify CAGF functions for MTL")
>
> So not DG1 and above?

The issue for DG1+ happens if non-freq bits are non-zero but freq bits are
zero. But we've already seen that during PMU freq sampling gt is unparked
so freq bits being 0 is rare. Therefore IMO there is 0 practical impact of
that bug, I don't think it's worth fixing it and Cc'ing stable etc. (also
those platforms are under force probe).

> > Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/8280
> > Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
> > ---
> >   drivers/gpu/drm/i915/gt/intel_rps.c | 46 +++++++++++++++++++----------
> >   drivers/gpu/drm/i915/gt/intel_rps.h |  2 +-
> >   drivers/gpu/drm/i915/i915_pmu.c     | 10 +++----
> >   3 files changed, 36 insertions(+), 22 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/intel_rps.c b/drivers/gpu/drm/i915/gt/intel_rps.c
> > index 4d0dc9de23f9..3957c5ee5cba 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_rps.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_rps.c
> > @@ -2046,16 +2046,6 @@ void intel_rps_sanitize(struct intel_rps *rps)
> >		rps_disable_interrupts(rps);
> >   }
> >   -u32 intel_rps_read_rpstat_fw(struct intel_rps *rps)
> > -{
> > -	struct drm_i915_private *i915 = rps_to_i915(rps);
> > -	i915_reg_t rpstat;
> > -
> > -	rpstat = (GRAPHICS_VER(i915) >= 12) ? GEN12_RPSTAT1 : GEN6_RPSTAT1;
> > -
> > -	return intel_uncore_read_fw(rps_to_gt(rps)->uncore, rpstat);
> > -}
> > -
> >   u32 intel_rps_read_rpstat(struct intel_rps *rps)
> >   {
> >	struct drm_i915_private *i915 = rps_to_i915(rps);
> > @@ -2089,10 +2079,11 @@ u32 intel_rps_get_cagf(struct intel_rps *rps, u32 rpstat)
> >	return cagf;
> >   }
> >   -static u32 read_cagf(struct intel_rps *rps)
> > +static u32 __read_cagf(struct intel_rps *rps, bool take_fw)
> >   {
> >	struct drm_i915_private *i915 = rps_to_i915(rps);
> >	struct intel_uncore *uncore = rps_to_uncore(rps);
> > +	i915_reg_t r = INVALID_MMIO_REG;
> >	u32 freq;
> >		/*
> > @@ -2100,22 +2091,30 @@ static u32 read_cagf(struct intel_rps *rps)
> >	 * registers will return 0 freq when GT is in RC6
> >	 */
> >	if (GRAPHICS_VER_FULL(i915) >= IP_VER(12, 70)) {
> > -		freq = intel_uncore_read(uncore, MTL_MIRROR_TARGET_WP1);
> > +		r = MTL_MIRROR_TARGET_WP1;
> >	} else if (GRAPHICS_VER(i915) >= 12) {
> > -		freq = intel_uncore_read(uncore, GEN12_RPSTAT1);
> > +		r = GEN12_RPSTAT1;
> >	} else if (IS_VALLEYVIEW(i915) || IS_CHERRYVIEW(i915)) {
> >		vlv_punit_get(i915);
> >		freq = vlv_punit_read(i915, PUNIT_REG_GPU_FREQ_STS);
> >		vlv_punit_put(i915);
> > +		goto exit;
> >	} else if (GRAPHICS_VER(i915) >= 6) {
> > -		freq = intel_uncore_read(uncore, GEN6_RPSTAT1);
> > +		r = GEN6_RPSTAT1;
> >	} else {
> > -		freq = intel_uncore_read(uncore, MEMSTAT_ILK);
> > +		r = MEMSTAT_ILK;
> >	}
> >   +	freq = take_fw ? intel_uncore_read(uncore, r) :
> > intel_uncore_read_fw(uncore, r);
> > +exit:
> >	return intel_rps_get_cagf(rps, freq);
> >   }
> >   +static u32 read_cagf(struct intel_rps *rps)
> > +{
> > +	return __read_cagf(rps, true);
> > +}
> > +
> >   u32 intel_rps_read_actual_frequency(struct intel_rps *rps)
> >   {
> >	struct intel_runtime_pm *rpm = rps_to_uncore(rps)->rpm;
> > @@ -2128,6 +2127,23 @@ u32 intel_rps_read_actual_frequency(struct intel_rps *rps)
> >	return freq;
> >   }
> >   +static u32 read_cagf_fw(struct intel_rps *rps)
> > +{
> > +	return __read_cagf(rps, false);
> > +}
> > +
> > +u32 intel_rps_read_actual_frequency_fw(struct intel_rps *rps)
> > +{
> > +	struct intel_runtime_pm *rpm = rps_to_uncore(rps)->rpm;
> > +	intel_wakeref_t wakeref;
> > +	u32 freq = 0;
> > +
> > +	with_intel_runtime_pm_if_in_use(rpm, wakeref)
>
> When called from i915_pmu.c::frequency sample() above seems redundant since
> there we already are under intel_gt_pm_get_if_awake. Perhaps it is not a
> huge deal but it is nevertheless wasteful.
>
> Also, maybe I am a bit rusty, but more fundamentally, wouldn't this be
> adding a _very_ atypical pattern of a _fw function which grabs rpm? I'd
> expect they all assume it's already held since the forcewake is already
> held.
>
> Am I missing the reason why it is needed?

Thanks for catching this, you are right, it was just mindless copy paste,
I've dropped it in the next version.

Thanks.
--
Ashutosh