Re: [PATCH 1/3] drm/i915: Use intel_engine_stop_cs when stopping ringbuffer

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> Quoting Mika Kuoppala (2019-02-28 16:14:11)
>> We have an exported function for stopping the engine before
>> disabling a ringbuffer. Take it into use.
>> 
>> v2: use fw on empty check
>> v3: tail is tail
>> 
>> Cc: Chris Wilson <chris@chris-wilson.co.uk>
>> Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
>> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
>> ---
>>  drivers/gpu/drm/i915/intel_engine_cs.c  |  3 ++
>>  drivers/gpu/drm/i915/intel_ringbuffer.c | 41 ++++++++++++++-----------
>>  2 files changed, 26 insertions(+), 18 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
>> index df8f88142f1d..e35dc0386bf6 100644
>> --- a/drivers/gpu/drm/i915/intel_engine_cs.c
>> +++ b/drivers/gpu/drm/i915/intel_engine_cs.c
>> @@ -856,6 +856,9 @@ void intel_engine_cancel_stop_cs(struct intel_engine_cs *engine)
>>  {
>>         struct drm_i915_private *dev_priv = engine->i915;
>>  
>> +       if (INTEL_GEN(dev_priv) < 3)
>> +               return;
>> +
>>         GEM_TRACE("%s\n", engine->name);
>>  
>>         I915_WRITE_FW(RING_MI_MODE(engine->mmio_base),
>> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
>> index 1b96b0960adc..5fe28d9087b7 100644
>> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
>> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
>> @@ -604,26 +604,32 @@ static void ring_setup_status_page(struct intel_engine_cs *engine)
>>         flush_cs_tlb(engine);
>>  }
>>  
>> +static bool ring_is_empty(struct intel_engine_cs *engine)
>> +{
>> +       struct drm_i915_private *dev_priv = engine->i915;
>> +       const u32 base = engine->mmio_base;
>> +
>> +       return (I915_READ_FW(RING_HEAD(base)) & HEAD_ADDR) ==
>> +               (I915_READ_FW(RING_TAIL(base)) & TAIL_ADDR);
>> +}
>> +
>>  static bool stop_ring(struct intel_engine_cs *engine)
>>  {
>>         struct drm_i915_private *dev_priv = engine->i915;
>> +       int ret;
>>  
>> -       if (INTEL_GEN(dev_priv) > 2) {
>> -               I915_WRITE_MODE(engine, _MASKED_BIT_ENABLE(STOP_RING));
>> -               if (intel_wait_for_register(dev_priv,
>> -                                           RING_MI_MODE(engine->mmio_base),
>> -                                           MODE_IDLE,
>> -                                           MODE_IDLE,
>> -                                           1000)) {
>> -                       DRM_ERROR("%s : timed out trying to stop ring\n",
>> -                                 engine->name);
>> -                       /* Sometimes we observe that the idle flag is not
>> -                        * set even though the ring is empty. So double
>> -                        * check before giving up.
>> -                        */
>> -                       if (I915_READ_HEAD(engine) != I915_READ_TAIL(engine))
>> -                               return false;
>> -               }
>> +       ret = intel_engine_stop_cs(engine);
>> +       if (ret == -ENODEV)
>> +               ret = 0;
>> +
>> +       if (ret) {
>> +               /*
>> +                * Sometimes we observe that the idle flag is not
>> +                * set even though the ring is empty. So double
>> +                * check before giving up.
>> +                */
>> +               if (!ring_is_empty(engine))
>> +                       return false;
>
> Hmm, thinking more about this, shouldn't we push this down to stop_cs()?
>
> If that's reporting an error in a situation where we can determine that
> the ring is idle anyway, we can report the stop_cs succeeded.

Makes sense, I will take a look.

I felt small urge to deflate the 'stop'.

Would it be confusing if we just did
intel_engine_start|stop instead of stop_cs and
cancel_stop_cs?

So hmm:

intel_engine_start()
intel_engine_stop()

these would only toggle the STOP_RING

and for replacing stop_ring with:
intel_engine_empty_ring()

for zeroing the heads.

one 'stop' to rule the (ring)world!?

-Mika
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