Re: [Intel-gfx] [PATCH v2] drm/i915/guc: Disable PL1 power limit when loading GuC firmware

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 13 Mar 2023, Ashutosh Dixit <ashutosh.dixit@intel.com> wrote:
> On dGfx, the PL1 power limit being enabled and set to a low value results
> in a low GPU operating freq. It also negates the freq raise operation which
> is done before GuC firmware load. As a result GuC firmware load can time
> out. Such timeouts were seen in the GL #8062 bug below (where the PL1 power
> limit was enabled and set to a low value). Therefore disable the PL1 power
> limit when allowed by HW when loading GuC firmware.
>
> v2:
>  - Take mutex (to disallow writes to power1_max) across GuC reset/fw load
>  - Add hwm_power_max_restore to error return code path
>
> Link: https://gitlab.freedesktop.org/drm/intel/-/issues/8062
> Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
> ---
>  drivers/gpu/drm/i915/gt/uc/intel_uc.c | 10 ++++++-
>  drivers/gpu/drm/i915/i915_hwmon.c     | 39 +++++++++++++++++++++++++++
>  drivers/gpu/drm/i915/i915_hwmon.h     |  7 +++++
>  3 files changed, 55 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_uc.c b/drivers/gpu/drm/i915/gt/uc/intel_uc.c
> index 4ccb4be4c9cb..15f8e94edc61 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_uc.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_uc.c
> @@ -18,6 +18,7 @@
>  #include "intel_uc.h"
>  
>  #include "i915_drv.h"
> +#include "i915_hwmon.h"
>  
>  static const struct intel_uc_ops uc_ops_off;
>  static const struct intel_uc_ops uc_ops_on;
> @@ -460,7 +461,7 @@ static int __uc_init_hw(struct intel_uc *uc)
>  	struct drm_i915_private *i915 = gt->i915;
>  	struct intel_guc *guc = &uc->guc;
>  	struct intel_huc *huc = &uc->huc;
> -	int ret, attempts;
> +	int ret, attempts, pl1en;
>  
>  	GEM_BUG_ON(!intel_uc_supports_guc(uc));
>  	GEM_BUG_ON(!intel_uc_wants_guc(uc));
> @@ -491,6 +492,9 @@ static int __uc_init_hw(struct intel_uc *uc)
>  	else
>  		attempts = 1;
>  
> +	/* Disable PL1 limit before raising freq */

That's just duplicating what the code says; a few words on the why might
be helpful.

> +	hwm_power_max_disable(gt, &pl1en);
> +
>  	intel_rps_raise_unslice(&uc_to_gt(uc)->rps);
>  
>  	while (attempts--) {
> @@ -547,6 +551,8 @@ static int __uc_init_hw(struct intel_uc *uc)
>  		intel_rps_lower_unslice(&uc_to_gt(uc)->rps);
>  	}
>  
> +	hwm_power_max_restore(gt, pl1en); /* Restore PL1 limit */
> +
>  	guc_info(guc, "submission %s\n", str_enabled_disabled(intel_uc_uses_guc_submission(uc)));
>  	guc_info(guc, "SLPC %s\n", str_enabled_disabled(intel_uc_uses_guc_slpc(uc)));
>  
> @@ -563,6 +569,8 @@ static int __uc_init_hw(struct intel_uc *uc)
>  	/* Return GT back to RPn */
>  	intel_rps_lower_unslice(&uc_to_gt(uc)->rps);
>  
> +	hwm_power_max_restore(gt, pl1en); /* Restore PL1 limit */

Ditto about code and comment duplicating the same thing.

Also, we don't use end of the line comments very much. 

> +
>  	__uc_sanitize(uc);
>  
>  	if (!ret) {
> diff --git a/drivers/gpu/drm/i915/i915_hwmon.c b/drivers/gpu/drm/i915/i915_hwmon.c
> index ee63a8fd88fc..2bbca75ac477 100644
> --- a/drivers/gpu/drm/i915/i915_hwmon.c
> +++ b/drivers/gpu/drm/i915/i915_hwmon.c
> @@ -444,6 +444,45 @@ hwm_power_write(struct hwm_drvdata *ddat, u32 attr, int chan, long val)
>  	}
>  }
>  
> +void hwm_power_max_disable(struct intel_gt *gt, u32 *old)
> +{
> +	struct i915_hwmon *hwmon = gt->i915->hwmon;
> +	intel_wakeref_t wakeref;
> +	u32 r;
> +
> +	if (!hwmon || !i915_mmio_reg_valid(hwmon->rg.pkg_rapl_limit))
> +		return;
> +
> +	/* Take mutex to prevent concurrent hwm_power_max_write */
> +	mutex_lock(&hwmon->hwmon_lock);
> +
> +	with_intel_runtime_pm(hwmon->ddat.uncore->rpm, wakeref)
> +		r = intel_uncore_rmw(hwmon->ddat.uncore,
> +				     hwmon->rg.pkg_rapl_limit,
> +				     PKG_PWR_LIM_1_EN, 0);
> +
> +	*old = !!(r & PKG_PWR_LIM_1_EN);

If you only need a bool, why do you use a u32?

> +
> +	/* hwmon_lock mutex is unlocked in hwm_power_max_restore */

Not too happy about that... any better ideas?

At the very minimum the functions need locking annotations. Otherwise
we'll get an influx of static analyser complaints.

> +}
> +
> +void hwm_power_max_restore(struct intel_gt *gt, u32 old)
> +{
> +	struct i915_hwmon *hwmon = gt->i915->hwmon;
> +	intel_wakeref_t wakeref;
> +
> +	if (!hwmon || !i915_mmio_reg_valid(hwmon->rg.pkg_rapl_limit))
> +		return;
> +
> +	with_intel_runtime_pm(hwmon->ddat.uncore->rpm, wakeref)
> +		intel_uncore_rmw(hwmon->ddat.uncore,
> +				 hwmon->rg.pkg_rapl_limit,
> +				 PKG_PWR_LIM_1_EN,
> +				 old ? PKG_PWR_LIM_1_EN : 0);
> +
> +	mutex_unlock(&hwmon->hwmon_lock);
> +}
> +
>  static umode_t
>  hwm_energy_is_visible(const struct hwm_drvdata *ddat, u32 attr)
>  {
> diff --git a/drivers/gpu/drm/i915/i915_hwmon.h b/drivers/gpu/drm/i915/i915_hwmon.h
> index 7ca9cf2c34c9..0c2db11be2e2 100644
> --- a/drivers/gpu/drm/i915/i915_hwmon.h
> +++ b/drivers/gpu/drm/i915/i915_hwmon.h
> @@ -7,14 +7,21 @@
>  #ifndef __I915_HWMON_H__
>  #define __I915_HWMON_H__
>  
> +#include <linux/types.h>
> +
>  struct drm_i915_private;
> +struct intel_gt;
>  
>  #if IS_REACHABLE(CONFIG_HWMON)
>  void i915_hwmon_register(struct drm_i915_private *i915);
>  void i915_hwmon_unregister(struct drm_i915_private *i915);
> +void hwm_power_max_disable(struct intel_gt *gt, u32 *old);
> +void hwm_power_max_restore(struct intel_gt *gt, u32 old);

Naming should be i915_hwmon_ prefixed following the usual conventions.

Why is the variable intel_gt instead of i915? There's nothing gt
specific in the added code?

>  #else
>  static inline void i915_hwmon_register(struct drm_i915_private *i915) { };
>  static inline void i915_hwmon_unregister(struct drm_i915_private *i915) { };
> +void hwm_power_max_disable(struct intel_gt *gt, u32 *old) { };
> +void hwm_power_max_restore(struct intel_gt *gt, u32 old) { };

These need to be static inline.

BR,
Jani.

>  #endif
>  
>  #endif /* __I915_HWMON_H__ */

-- 
Jani Nikula, Intel Open Source Graphics Center