[PATCH v6 3/4] drm/i915: Reset steer semaphore for media GT on resume

[Matt Roper]

On Wed, Sep 27, 2023 at 11:03:56PM +0200, Nirmoy Das wrote:
> During resume, the steer semaphore on GT1 was observed to be held. The
> hardware team has confirmed the safety of clearing the steer semaphore
> during driver load/resume, as no lock acquisitions can occur in this
> process by other agents.

I guess the question is whether we just want to handle the one case
where we've already seen a BIOS snapshot screw up (i.e., specifically on
GT1 during resume), or do we want to make this a general sanitization
that we do on both GTs at both load and resume, just to be safe?  Given
that the hardware team has indicated no external agents would be
expected to be using steering at the point the driver is
loading/resuming, maybe it's best to always do the sanitization on
platforms that have a hardware semaphore?


Matt

> 
> v2: reset on resume not in intel_gt_init().
> v3: do the reset on intel_gt_resume_early()
> 
> Signed-off-by: Nirmoy Das <nirmoy.das at intel.com>
> ---
>  drivers/gpu/drm/i915/gt/intel_gt_pm.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_gt_pm.c b/drivers/gpu/drm/i915/gt/intel_gt_pm.c
> index dab73980c9f1..59cebf205b72 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gt_pm.c
> +++ b/drivers/gpu/drm/i915/gt/intel_gt_pm.c
> @@ -13,6 +13,7 @@
>  #include "intel_engine_pm.h"
>  #include "intel_gt.h"
>  #include "intel_gt_clock_utils.h"
> +#include "intel_gt_mcr.h"
>  #include "intel_gt_pm.h"
>  #include "intel_gt_print.h"
>  #include "intel_gt_requests.h"
> @@ -218,6 +219,17 @@ void intel_gt_pm_fini(struct intel_gt *gt)
>  
>  void intel_gt_resume_early(struct intel_gt *gt)
>  {
> +	/*
> +	 * Reset the steer semaphore on GT1, as we have observed it
> +	 * remaining held after a suspend operation. Confirmation
> +	 * from the hardware team ensures the safety of resetting
> +	 * the steer semaphore during driver load/resume, as there
> +	 * are no lock acquisitions during this process by other
> +	 * agents.
> +	 */
> +	if (MEDIA_VER(gt->i915) >= 13 && gt->type == GT_MEDIA)
> +		intel_gt_mcr_lock_reset(gt);
> +
>  	intel_uncore_resume_early(gt->uncore);
>  	intel_gt_check_and_clear_faults(gt);
>  }
> -- 
> 2.41.0
> 

-- 
Matt Roper
Graphics Software Engineer
Linux GPU Platform Enablement
Intel Corporation