Re: [Intel-gfx] [PATCH 2/2] drm/i915/pmu: Remove fallback to requested freq for SLPC

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 10/03/2023 00:59, Ashutosh Dixit wrote:
> The fallback to requested freq does not work for SLPC because SLPC does not
> use 'struct intel_rps'. Also for SLPC requested freq can only be obtained
> from a hw register after acquiring forcewake which we don't want to do for
> PMU. Therefore remove fallback to requested freq for SLPC. The actual freq
> will be 0 when gt is in RC6 which is correct. Also this is rare since PMU
> freq sampling happens only when gt is unparked.
> 
> Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
> ---
>   drivers/gpu/drm/i915/i915_pmu.c | 9 ++++++++-
>   1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
> index 7ece883a7d95..f697fabed64a 100644
> --- a/drivers/gpu/drm/i915/i915_pmu.c
> +++ b/drivers/gpu/drm/i915/i915_pmu.c
> @@ -393,7 +393,14 @@ frequency_sample(struct intel_gt *gt, unsigned int period_ns)
>   		 * frequency. Fortunately, the read should rarely fail!
>   		 */
>   		val = intel_rps_read_actual_frequency_fw(rps);
> -		if (!val)
> +
> +		/*
> +		 * SLPC does not use 'struct intel_rps'. Also for SLPC
> +		 * requested freq can only be obtained after acquiring
> +		 * forcewake and reading a hw register. For SLPC just
> +		 * let val be 0
> +		 */
> +		if (!val && !intel_uc_uses_guc_slpc(&gt->uc))
>   			val = intel_gpu_freq(rps, rps->cur_freq);

I really dislike sprinkling of "uses slpc" since I think the thing 
hasn't really been integrated nicely. Case in point is probably the flow 
duality in intel_rps_boost. Data structures as well, even though some 
fields and concepts are shared.

For instance why we can't have the notion of software tracked cur_freq 
in rps, and/or have it zero if with SLPC we can't have it otherwise?

I will abstain, sorry.

Regards,

Tvrtko

>   
>   		add_sample_mult(&pmu->sample[__I915_SAMPLE_FREQ_ACT],