Re: [PATCH 1/2] drm/i915: Improve irq handling after gpu resets

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

On Thu, May 22, 2014 at 10:18:21PM +0200, Daniel Vetter wrote:
> Currently we do a full re-init of all interrupts after a gpu hang.
> Which is pretty bad since we don't restore the interrupts we've
> enabled at runtime correctly. Even with that addressed it's rather
> horribly race.
> 
> But on g4x and later we only reset the gt and not the entire gpu.
> Which means we only need to reset the GT interrupt bits. Which has the
> nice benefit that vblank waits, pipe CRC interrupts and everything
> else display related just keeps on working.
> 
> The downside is that gt interrupt handling (i.e. ring->get/put_irq) is
> still racy. But as long as the gpu hang reliably wakes all waters and
> we have a short time where the refcount drops to 0 we'll recover. So
> not that bad really.
> 
> v2: Ville noticed that GTIMR and PMIMR don't get cleared, only the
> subordinate per-ring registers. So let's rip out all the interrupt dancing.
> The FIXME comment is still required though since the ring irq handling
> happens at the per-ring interrupt mask registers, too.
> 
> Testcase: igt/kms_flip/vblank-vs-hang
> Testcase: igt/kms_pipe_crc_basic/hang-*
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Both patches:
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

And to answer you earlier question, yes things seemd to work fine after
a GPU reset if I didn't touch the interrupt registers. In fact I also
tried killing most of the gem_hw_init() stuff (basically just left
ring->init(), l3_remap, and context enable) and things still seemed to
work just fine.

> ---
>  drivers/gpu/drm/i915/i915_drv.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> index c83c83b74bf4..7ae906c811bb 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -811,17 +811,17 @@ int i915_reset(struct drm_device *dev)
>  		}
>  
>  		/*
> -		 * FIXME: This is horribly race against concurrent pageflip and
> -		 * vblank wait ioctls since they can observe dev->irqs_disabled
> -		 * being false when they shouldn't be able to.
> +		 * FIXME: This races pretty badly against concurrent holders of
> +		 * ring interrupts. This is possible since we've started to drop
> +		 * dev->struct_mutex in select places when waiting for the gpu.
>  		 */
> -		drm_irq_uninstall(dev);
> -		drm_irq_install(dev, dev->pdev->irq);
>  
> -		/* rps/rc6 re-init is necessary to restore state lost after the
> -		 * reset and the re-install of drm irq. Skip for ironlake per
> +		/*
> +		 * rps/rc6 re-init is necessary to restore state lost after the
> +		 * reset and the re-install of gt irqs. Skip for ironlake per
>  		 * previous concerns that it doesn't respond well to some forms
> -		 * of re-init after reset. */
> +		 * of re-init after reset.
> +		 */
>  		if (INTEL_INFO(dev)->gen > 5)
>  			intel_reset_gt_powersave(dev);

I'm suspecting that GPU reset doesn't affect the RPS/RC6 stuff either.
But I suppose it shouldn't really hurt anything to do it, so it's just
something to look into if we want to reduce the amount of stuff we do
at reset.

-- 
Ville Syrjälä
Intel OTC