Re: [PATCH 08/17] drm/i915: Forcefully flush GuC log buffer on reset

["Goel, Akash" <akash.goel@intel.com>]

On 7/20/2016 2:42 PM, Chris Wilson wrote:
> On Wed, Jul 20, 2016 at 09:51:45AM +0530, Goel, Akash wrote:
>>
>>
>> On 7/19/2016 4:51 PM, Chris Wilson wrote:
>>> On Tue, Jul 19, 2016 at 12:12:20PM +0100, Tvrtko Ursulin wrote:
>>>>
>>>> On 10/07/16 14:41, akash.goel@intel.com wrote:
>>>>> From: Sagar Arun Kamble <sagar.a.kamble@intel.com>
>>>>>
>>>>> If GuC logs are being captured, there should be a force log buffer flush
>>>>> action sent to GuC before proceeding with GPU reset and re-initializing
>>>>> GUC. Those logs would be useful to understand why the GPU reset was
>>>>> initiated.
>>>>>
>>>>> v2: Rebase.
>>>>>
>>>>> Signed-off-by: Sagar Arun Kamble <sagar.a.kamble@intel.com>
>>>>> Signed-off-by: Akash Goel <akash.goel@intel.com>
>>>>> ---
>>>>> drivers/gpu/drm/i915/i915_guc_submission.c | 32 ++++++++++++++++++++++++++++++
>>>>> drivers/gpu/drm/i915/i915_irq.c            |  2 ++
>>>>> drivers/gpu/drm/i915/intel_guc.h           |  1 +
>>>>> 3 files changed, 35 insertions(+)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
>>>>> index 9b436fa..8cc31c6 100644
>>>>> --- a/drivers/gpu/drm/i915/i915_guc_submission.c
>>>>> +++ b/drivers/gpu/drm/i915/i915_guc_submission.c
>>>>> @@ -183,6 +183,16 @@ static int host2guc_logbuffer_flush_complete(struct intel_guc *guc)
>>>>> 	return host2guc_action(guc, data, 1);
>>>>> }
>>>>>
>>>>> +static int host2guc_force_logbuffer_flush(struct intel_guc *guc)
>>>>> +{
>>>>> +	u32 data[2];
>>>>> +
>>>>> +	data[0] = HOST2GUC_ACTION_FORCE_LOG_BUFFER_FLUSH;
>>>>> +	data[1] = 0;
>>>>> +
>>>>> +	return host2guc_action(guc, data, 2);
>>>>> +}
>>>>> +
>>>>> /*
>>>>>  * Initialise, update, or clear doorbell data shared with the GuC
>>>>>  *
>>>>> @@ -1404,6 +1414,28 @@ void i915_guc_capture_logs(struct drm_device *dev)
>>>>> 	intel_runtime_pm_put(dev_priv);
>>>>> }
>>>>>
>>>>> +void i915_guc_capture_logs_on_reset(struct drm_device *dev)
>>>>> +{
>>>>> +	struct drm_i915_private *dev_priv = dev->dev_private;
>>>>> +
>>>>> +	mutex_lock(&dev->struct_mutex);
>>>>
>>>> Not sure what are the repercussion of taking the mutex on the
>>>> i915_reset_and_wakeup and path (error capture, hangcheck, dont' know
>>>> this area well). Check with Chris and Mika I suppose (cc-ed)?
>>>
>>
>> Took the struct_mutex, just to avoid a very remote possibility where
>> i915_guc_capture_logs_on_reset & debugfs function
>> i915_guc_log_control executes concurrently.
>>
>>> Flat out invalid to take struct_mutex on the error capture path, or any
>>> lock at all really (just in case of driver bugs). Consider it to be an
>>> atomic context that may preempt the driver at any point.
>>
>> Actually I see that i915_reset() too takes the struct_mutex right at
>> the beginning and I have plugged the call to
>> i915_guc_capture_logs_on_reset() just before that.
>
> Postmortem state is captured from i915_capture_error_state(), and as I
> recall one of the raison d'etre for this facility was to include the guc
> log in the error state.

Sorry I missed augmenting the error state with guc firmware logs.
For that also a prior flush will be needed, will do the flush without 
acquiring the struct_mutex.

Best regards
Akash

> -Chris
>
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