Re: [PATCH] drm/i915: Clear pending reset requests during suspend

[Arun Siluvery <arun.siluvery@linux.intel.com>]

On 19/01/2016 14:13, Chris Wilson wrote:
> On Tue, Jan 19, 2016 at 03:04:40PM +0100, Daniel Vetter wrote:
>> On Tue, Jan 19, 2016 at 01:48:05PM +0000, Chris Wilson wrote:
>>> On Tue, Jan 19, 2016 at 01:09:28PM +0100, Daniel Vetter wrote:
>>>> On Thu, Jan 14, 2016 at 10:49:45AM +0000, Arun Siluvery wrote:
>>>>> Pending reset requests are cleared before suspending, they should be picked up
>>>>> after resume when new work is submitted.
>>>>>
>>>>> This is originally added as part of TDR patches for Gen8 from Tomas Elf which
>>>>> are under review, as suggested by Chris this is extracted as a separate patch
>>>>> as it can be useful now.
>>>>>
>>>>> Cc: Mika Kuoppala <mika.kuoppala@intel.com>
>>>>> Cc: Chris Wilson <chris@chris-wilson.co.uk>
>>>>> Signed-off-by: Arun Siluvery <arun.siluvery@linux.intel.com>
>>>>
>>>> Pulling in the discussion we had from irc: Imo the right approach is to
>>>> simply wait for gpu reset to finish it's job. Since that could in turn
>>>> lead to a dead gpu (if we're unlucky and init_hw failed) we'd need to do
>>>> that in a loop around gem_idle. And drop dev->struct_mutex in-between.
>>>> E.g.
>>>>
>>>> while (busy) {
>>>> 	mutex_lock();
>>>> 	gpu_idle();
>>>> 	mutex_unlock();
>>>>
>>>> 	flush_work(reset_work);
>>>> }
>>>
>>> Where does the requirement for gpu_idle come from? If there is a global
>>> reset in progress, it cannot queue a request to flush the work and
>>> waiting on the old results will be skipped. So just wait for the global
>>> reset to complete, i.e. flush_work().
>>
>> Yes, but the global reset might in turn leave a wrecked gpu behind, or at
>> least a non-idle one. Hence another gpu_idle on top, to make sure. If we
>> change init_hw() of engines to be synchronous then we should have at least
>> a WARN_ON(not_idle_but_i_expected_so()); in there ...

gpu_error.work is removed in b8d24a06568368076ebd5a858a011699a97bfa42, 
we are doing reset in hangcheck work itself so I think there is no need 
to flush work.

while (i915_reset_in_progress(gpu_error) &&
        !i915_terminally_wedged(gpu_error)) {
         int ret;

         mutex_lock(&dev->struct_mutex);
         ret = i915_gpu_idle(dev);
         if (ret)
                 DRM_ERROR("GPU is in inconsistent state after reset\n");
         mutex_unlock(&dev->struct_mutex);
}

If the reset is successful we are idle before suspend otherwise in a 
wedged state. is this ok?

regards
Arun

>
> Does it matter on suspend? We test on resume if the GPU is usable, but
> if we wanted to test on suspend then we should do
>
> flush_work();
> if (i915_terminally_wedged())
>     /* oh noes */;
> -Chris
>

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