Re: [PATCH v2] drm/i915: Wait for gen3 reset status to be asserted

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> After we assert the reset request (and wait for 20us), when the device
> has been fully reset it asserts the reset-status bit. Before we stop
> requesting the reset and allow the device to return to normal, we should
> wait for the reset to be completed. (Similar to how we wait for the
> device to return to normal after deasserting the reset request.)
>
> v2: Rename i915_reset_completed() probe to not cause as much confusion.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_uncore.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index 0fd59dd6bbb5..e09981a3113c 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -1550,24 +1550,31 @@ static void i915_stop_engines(struct drm_i915_private *dev_priv,
>  		gen3_stop_engine(engine);
>  }
>  
> -static bool i915_reset_complete(struct pci_dev *pdev)
> +static bool i915_in_reset(struct pci_dev *pdev)
>  {
>  	u8 gdrst;
>  
>  	pci_read_config_byte(pdev, I915_GDRST, &gdrst);
> -	return (gdrst & GRDOM_RESET_STATUS) == 0;
> +	return gdrst & GRDOM_RESET_STATUS;
>  }
>  
>  static int i915_do_reset(struct drm_i915_private *dev_priv, unsigned engine_mask)
>  {
>  	struct pci_dev *pdev = dev_priv->drm.pdev;
> +	int err;
>  
> -	/* assert reset for at least 20 usec */
> +	/* Assert reset for at least 20 usec, and wait for acknowledgement. */
>  	pci_write_config_byte(pdev, I915_GDRST, GRDOM_RESET_ENABLE);
>  	usleep_range(50, 200);
> +	err = wait_for(i915_in_reset(pdev), 500);
> +
> +	/* Clear the reset request. */
>  	pci_write_config_byte(pdev, I915_GDRST, 0);
> +	usleep_range(50, 200);
> +	if (!err)
> +		err = wait_for(!i915_in_reset(pdev), 500);
>

Regardless of if this helps or not with pnv, it makes the
both phases clear.

Any thoughts of starting to log the reset attempts
with timeout, even if the subsequent reset succeeds?

Patch is,
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>

> -	return wait_for(i915_reset_complete(pdev), 500);
> +	return err;
>  }
>  
>  static bool g4x_reset_complete(struct pci_dev *pdev)
> -- 
> 2.16.1
>
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