Re: [Intel-gfx] [PATCH v3] drm/i915/slpc: Use platform limits for min/max frequency

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

On Tue, 18 Oct 2022 11:30:31 -0700, Vinay Belgaumkar wrote:
>

Hi Vinay,

> diff --git a/drivers/gpu/drm/i915/gt/selftest_slpc.c b/drivers/gpu/drm/i915/gt/selftest_slpc.c
> index 4c6e9257e593..e42bc215e54d 100644
> --- a/drivers/gpu/drm/i915/gt/selftest_slpc.c
> +++ b/drivers/gpu/drm/i915/gt/selftest_slpc.c
> @@ -234,6 +234,7 @@ static int run_test(struct intel_gt *gt, int test_type)
>	enum intel_engine_id id;
>	struct igt_spinner spin;
>	u32 slpc_min_freq, slpc_max_freq;
> +	u32 saved_min_freq;
>	int err = 0;
>
>	if (!intel_uc_uses_guc_slpc(&gt->uc))
> @@ -252,20 +253,35 @@ static int run_test(struct intel_gt *gt, int test_type)
>		return -EIO;
>	}
>
> -	/*
> -	 * FIXME: With efficient frequency enabled, GuC can request
> -	 * frequencies higher than the SLPC max. While this is fixed
> -	 * in GuC, we level set these tests with RPn as min.
> -	 */
> -	err = slpc_set_min_freq(slpc, slpc->min_freq);
> -	if (err)
> -		return err;
> +	if (slpc_min_freq == slpc_max_freq) {
> +		/* Server parts will have min/max clamped to RP0 */
> +		if (slpc->min_is_rpmax) {
> +			err = slpc_set_min_freq(slpc, slpc->min_freq);
> +			if (err) {
> +				pr_err("Unable to update min freq on server part");
> +				return err;
> +			}
>
> -	if (slpc->min_freq == slpc->rp0_freq) {
> -		pr_err("Min/Max are fused to the same value\n");
> -		return -EINVAL;
> +		} else {
> +			pr_err("Min/Max are fused to the same value\n");
> +			return -EINVAL;

Sorry but I am not following this else case here. Why are we saying min/max
are fused to the same value? In this case we can't do
"slpc_set_min_freq(slpc, slpc->min_freq)" ? That is, we can't change SLPC
min freq?

> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_slpc.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_slpc.c
> index fdd895f73f9f..b7cdeec44bd3 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_slpc.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_slpc.c
> @@ -263,6 +263,7 @@ int intel_guc_slpc_init(struct intel_guc_slpc *slpc)
>
>	slpc->max_freq_softlimit = 0;
>	slpc->min_freq_softlimit = 0;
> +	slpc->min_is_rpmax = false;
>
>	slpc->boost_freq = 0;
>	atomic_set(&slpc->num_waiters, 0);
> @@ -588,6 +589,32 @@ static int slpc_set_softlimits(struct intel_guc_slpc *slpc)
>	return 0;
>  }
>
> +static bool is_slpc_min_freq_rpmax(struct intel_guc_slpc *slpc)
> +{
> +	int slpc_min_freq;
> +
> +	if (intel_guc_slpc_get_min_freq(slpc, &slpc_min_freq))
> +		return false;

I am wondering what happens if the above fails on server? Should we return
true or false on server and what are the consequences of returning false on
server?

Any case I think we should at least put a drm_err or something here just in
case this ever fails so we'll know something weird happened.

> +
> +	if (slpc_min_freq == SLPC_MAX_FREQ_MHZ)
> +		return true;
> +	else
> +		return false;
> +}
> +
> +static void update_server_min_softlimit(struct intel_guc_slpc *slpc)
> +{
> +	/* For server parts, SLPC min will be at RPMax.
> +	 * Use min softlimit to clamp it to RP0 instead.
> +	 */
> +	if (is_slpc_min_freq_rpmax(slpc) &&
> +	    !slpc->min_freq_softlimit) {
> +		slpc->min_is_rpmax = true;
> +		slpc->min_freq_softlimit = slpc->rp0_freq;
> +		(slpc_to_gt(slpc))->defaults.min_freq = slpc->min_freq_softlimit;
> +	}
> +}
> +
>  static int slpc_use_fused_rp0(struct intel_guc_slpc *slpc)
>  {
>	/* Force SLPC to used platform rp0 */
> @@ -647,6 +674,9 @@ int intel_guc_slpc_enable(struct intel_guc_slpc *slpc)
>
>	slpc_get_rp_values(slpc);
>
> +	/* Handle the case where min=max=RPmax */
> +	update_server_min_softlimit(slpc);
> +
>	/* Set SLPC max limit to RP0 */
>	ret = slpc_use_fused_rp0(slpc);
>	if (unlikely(ret)) {
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_slpc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc_slpc.h
> index 82a98f78f96c..11975a31c9d0 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_slpc.h
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_slpc.h
> @@ -9,6 +9,8 @@
>  #include "intel_guc_submission.h"
>  #include "intel_guc_slpc_types.h"
>
> +#define SLPC_MAX_FREQ_MHZ 4250

This seems to be really a value (255 converted to freq) so seems ok to
intepret in MHz.

Thanks.
--
Ashutosh