Re: [PATCH] drm/i915/gt: Reset twice

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Mon, Dec 12, 2022 at 05:13:38PM +0100, Andi Shyti wrote:
> From: Chris Wilson <chris@chris-wilson.co.uk>
> 
> After applying an engine reset, on some platforms like Jasperlake, we
> occasionally detect that the engine state is not cleared until shortly
> after the resume. As we try to resume the engine with volatile internal
> state, the first request fails with a spurious CS event (it looks like
> it reports a lite-restore to the hung context, instead of the expected
> idle->active context switch).
> 
> Signed-off-by: Chris Wilson <hris@chris-wilson.co.uk>

There's a typo in the signature email I'm afraid...

Other than that, have we checked the possibility of using the driver-initiated-flr bit
instead of this second loop? That should be the right way to guarantee everything is
cleared on gen11+...

> Cc: stable@vger.kernel.org
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/gt/intel_reset.c | 34 ++++++++++++++++++++++-----
>  1 file changed, 28 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_reset.c b/drivers/gpu/drm/i915/gt/intel_reset.c
> index ffde89c5835a4..88dfc0c5316ff 100644
> --- a/drivers/gpu/drm/i915/gt/intel_reset.c
> +++ b/drivers/gpu/drm/i915/gt/intel_reset.c
> @@ -268,6 +268,7 @@ static int ilk_do_reset(struct intel_gt *gt, intel_engine_mask_t engine_mask,
>  static int gen6_hw_domain_reset(struct intel_gt *gt, u32 hw_domain_mask)
>  {
>  	struct intel_uncore *uncore = gt->uncore;
> +	int loops = 2;
>  	int err;
>  
>  	/*
> @@ -275,18 +276,39 @@ static int gen6_hw_domain_reset(struct intel_gt *gt, u32 hw_domain_mask)
>  	 * for fifo space for the write or forcewake the chip for
>  	 * the read
>  	 */
> -	intel_uncore_write_fw(uncore, GEN6_GDRST, hw_domain_mask);
> +	do {
> +		intel_uncore_write_fw(uncore, GEN6_GDRST, hw_domain_mask);
>  
> -	/* Wait for the device to ack the reset requests */
> -	err = __intel_wait_for_register_fw(uncore,
> -					   GEN6_GDRST, hw_domain_mask, 0,
> -					   500, 0,
> -					   NULL);
> +		/*
> +		 * Wait for the device to ack the reset requests.
> +		 *
> +		 * On some platforms, e.g. Jasperlake, we see see that the
> +		 * engine register state is not cleared until shortly after
> +		 * GDRST reports completion, causing a failure as we try
> +		 * to immediately resume while the internal state is still
> +		 * in flux. If we immediately repeat the reset, the second
> +		 * reset appears to serialise with the first, and since
> +		 * it is a no-op, the registers should retain their reset
> +		 * value. However, there is still a concern that upon
> +		 * leaving the second reset, the internal engine state
> +		 * is still in flux and not ready for resuming.
> +		 */
> +		err = __intel_wait_for_register_fw(uncore, GEN6_GDRST,
> +						   hw_domain_mask, 0,
> +						   2000, 0,
> +						   NULL);
> +	} while (err == 0 && --loops);
>  	if (err)
>  		GT_TRACE(gt,
>  			 "Wait for 0x%08x engines reset failed\n",
>  			 hw_domain_mask);
>  
> +	/*
> +	 * As we have observed that the engine state is still volatile
> +	 * after GDRST is acked, impose a small delay to let everything settle.
> +	 */
> +	udelay(50);
> +
>  	return err;
>  }
>  
> -- 
> 2.38.1
>