Re: [PATCH 2/2] drm/i915: Wait for gen3 reset status to be asserted

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Feb 07, 2018 at 04:41:43PM +0200, Ville Syrjälä wrote:
> On Wed, Feb 07, 2018 at 10:08:45AM +0000, Chris Wilson wrote:
> > 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.)
> > 
> > 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 | 12 ++++++++++--
> >  1 file changed, 10 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> > index 612aad205b59..dd86428774da 100644
> > --- a/drivers/gpu/drm/i915/intel_uncore.c
> > +++ b/drivers/gpu/drm/i915/intel_uncore.c
> > @@ -1555,19 +1555,27 @@ static bool i915_reset_complete(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;

Doh. Failed to notice this change. The function name is perhaps a bit
confusing now since it doesn't match the meaning of the g4x version.
Maybe rename this guy? i915_gpu_in_reset() or something?

> >  }
> >  
> >  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 */
> >  	pci_write_config_byte(pdev, I915_GDRST, GRDOM_RESET_ENABLE);
> >  	usleep_range(50, 200);
> > +
> > +	err = wait_for(i915_reset_complete(pdev), 500);
> 
> The hardware should indicate that it's in reset as long as we keep the
> reset asserted. So this looks like an obfuscated usleep(500) to me.
> Did you mean !reset_complete?
> 
> > +
> >  	pci_write_config_byte(pdev, I915_GDRST, 0);
> > +	usleep_range(50, 200);
> > +
> > +	if (!err)
> > +		err = wait_for(!i915_reset_complete(pdev), 500);
> >  
> > -	return wait_for(i915_reset_complete(pdev), 500);
> > +	return err;
> >  }
> >  
> >  static bool g4x_reset_complete(struct pci_dev *pdev)
> > -- 
> > 2.16.1
> 
> -- 
> Ville Syrjälä
> Intel OTC

-- 
Ville Syrjälä
Intel OTC
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