[Intel-gfx] [PATCH] drm/i915: Allow unready gpu to be reset on gen8

[Jani Nikula]

On Thu, 19 Nov 2015, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Thu, Nov 19, 2015 at 11:41:07AM +0200, Mika Kuoppala wrote:
>> Daniel Vetter <daniel at ffwll.ch> writes:
>> 
>> > On Mon, Nov 02, 2015 at 11:25:08AM +0200, Mika Kuoppala wrote:
>> >> Gen9 has had demonstrated cases where forcing a not ready gpu
>> >> into reset has caused system hang [1].
>> >> 
>> >> Gen8 has never to this date demonstrated such behaviour.
>> >> 
>> >> In our CI tests there have been two cases of bsw ending in a state
>> >> where it claims it is not ready for reset, based on reset request,
>> >> after gpu hang [2]. Both of these cases have happened with kernel
>> >> where there are lots of debugs enabled. So it is possible that
>> >> something timing related is at play here like that wait_for_register()
>> >> usleep wakeups collide badly with forcewake.
>> >> 
>> >> If we assume that gen8 is safe to reset even with claims of nonreadiness,
>> >> we can alleviate this situations by forcing a reset and revive the gpu.
>> >> Enhance logging so that it will be clear what conditions led to decision
>> >> of proceeding or bailing out, so that we will spot if this way of forcing
>> >> our will against gpu turns out to be foolhardy.
>> >> 
>> >> v2: - add bugzilla entry for bsw behaviour (Chris)
>> >>     - improve commit message
>> >> 
>> >> References [1]: https://bugs.freedesktop.org/show_bug.cgi?id=89959
>> >> References [2]: https://bugs.freedesktop.org/show_bug.cgi?id=92774
>> >> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
>> >> Cc: Tomi Sarvela <tomix.p.sarvela at intel.com>
>> >> Cc: Chris Wilson <chris at chris-wilson.co.uk>
>> >> Signed-off-by: Mika Kuoppala <mika.kuoppala at intel.com>
>> >> ---
>> >>  drivers/gpu/drm/i915/intel_uncore.c | 9 ++++++++-
>> >>  1 file changed, 8 insertions(+), 1 deletion(-)
>> >> 
>> >> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
>> >> index f0f97b2..47c17f2 100644
>> >> --- a/drivers/gpu/drm/i915/intel_uncore.c
>> >> +++ b/drivers/gpu/drm/i915/intel_uncore.c
>> >> @@ -1504,7 +1504,14 @@ not_ready:
>> >>  		I915_WRITE(RING_RESET_CTL(engine->mmio_base),
>> >>  			   _MASKED_BIT_DISABLE(RESET_CTL_REQUEST_RESET));
>> >>  
>> >> -	return -EIO;
>> >> +	if (INTEL_INFO(dev)->gen == 9) {
>> >> +		DRM_ERROR("Reset would risk system stability, bailing out\n");
>> >> +		return -EIO;
>> >> +	}
>> >> +
>> >> +	DRM_ERROR("Forcing non ready gpu into reset\n");
>> >
>> > DRM_ERROR will cause dmes-warn failures when running igt. If we agree that
>> > this is ok, it should be at most DRM_INFO. I'd got with DRM_DEBUG_DRIVER.
>> > Ack with that change.
>> 
>> This is in the category 'shouldn't never happen' so I would prefer
>> igt to complain loudly if it can't request reset.
>> 
>> The real culprit was forcewakes missing on reset path, so
>> this patch can be forgotten and only resurrected if,
>> even with forcewake fix in, gen8 fails to request reset.
>> 
>> Here is the patch that fixed the underlying issue:
>> 
>> commit 99106bc17e667989b4c0af0a6afcbd6ddbada8fb
>> Author: Mika Kuoppala <mika.kuoppala at linux.intel.com>
>> Date:   Thu Nov 5 13:11:38 2015 +0200
>> 
>>     drm/i915: Do graphics device reset under forcewake
>
> Oh that story. With the above explanation added to the commit message:
>
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

Mika, is this patch still relevant? Please repost with the above fixed
if it is.

BR,
Jani.


>
>> 
>> 
>> Thanks,
>> -Mika
>> 
>> > -Daniel
>> >
>> >> +
>> >> +	return gen6_do_reset(dev);
>> >>  }
>> >>  
>> >>  static int (*intel_get_gpu_reset(struct drm_device *dev))(struct drm_device *)
>> >> -- 
>> >> 2.5.0
>> >> 
>> >
>> > -- 
>> > Daniel Vetter
>> > Software Engineer, Intel Corporation
>> > http://blog.ffwll.ch

-- 
Jani Nikula, Intel Open Source Technology Center