Re: [PATCH v7 1/4] drm/i915: Introduce intel_gt_mcr_lock_sanitize()

[Andrzej Hajda <andrzej.hajda@xxxxxxxxx>]

On 28.09.2023 15:00, Nirmoy Das wrote:
> Implement intel_gt_mcr_lock_sanitize() to provide a mechanism
> for cleaning the steer semaphore when absolutely necessary.
>
> v2: remove unnecessary lock(Andi, Matt)
>      improve the kernel doc(Matt)
>      s/intel_gt_mcr_lock_clear/intel_gt_mcr_lock_sanitize
>
> Signed-off-by: Nirmoy Das <nirmoy.das@xxxxxxxxx>
> ---
>   drivers/gpu/drm/i915/gt/intel_gt_mcr.c | 22 ++++++++++++++++++++++
>   drivers/gpu/drm/i915/gt/intel_gt_mcr.h |  1 +
>   2 files changed, 23 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_gt_mcr.c b/drivers/gpu/drm/i915/gt/intel_gt_mcr.c
> index bf4a933de03a..326c2ed1d99b 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gt_mcr.c
> +++ b/drivers/gpu/drm/i915/gt/intel_gt_mcr.c
> @@ -419,6 +419,28 @@ void intel_gt_mcr_unlock(struct intel_gt *gt, unsigned long flags)
>   		intel_uncore_write_fw(gt->uncore, MTL_STEER_SEMAPHORE, 0x1);
>   }
>   
> +/**
> + * intel_gt_mcr_lock_sanitize - Sanitize MCR steering lock
> + * @gt: GT structure
> + *
> + * This will be used to sanitize the initial status of the hardware lock
> + * during driver load and resume since there won't be any concurrent access
> + * from other agents at those times, but it's possible that boot firmware
> + * may have left the lock in a bad state.
> + *
> + */
> +void intel_gt_mcr_lock_sanitize(struct intel_gt *gt)
> +{
> +	/*
> +	 * This gets called at load/resume time, so we shouldn't be
> +	 * racing with other driver threads grabbing the mcr lock.
> +	 */
> +	lockdep_assert_not_held(&gt->mcr_lock);
> +
> +	if (GRAPHICS_VER_FULL(gt->i915) >= IP_VER(12, 70))
> +		intel_uncore_write_fw(gt->uncore, MTL_STEER_SEMAPHORE, 0x1);

I wonder if it wouldn't be useful to check and report if it is locked 
before unconditional release, no strong feelings.

Reviewed-by: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>

Regards
Andrzej


> +}
> +
>   /**
>    * intel_gt_mcr_read - read a specific instance of an MCR register
>    * @gt: GT structure
> diff --git a/drivers/gpu/drm/i915/gt/intel_gt_mcr.h b/drivers/gpu/drm/i915/gt/intel_gt_mcr.h
> index 41684495b7da..01ac565a56a4 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gt_mcr.h
> +++ b/drivers/gpu/drm/i915/gt/intel_gt_mcr.h
> @@ -11,6 +11,7 @@
>   void intel_gt_mcr_init(struct intel_gt *gt);
>   void intel_gt_mcr_lock(struct intel_gt *gt, unsigned long *flags);
>   void intel_gt_mcr_unlock(struct intel_gt *gt, unsigned long flags);
> +void intel_gt_mcr_lock_sanitize(struct intel_gt *gt);
>   
>   u32 intel_gt_mcr_read(struct intel_gt *gt,
>   		      i915_mcr_reg_t reg,