Re: [PATCH 1/4] drm/i915: Avoid EBUSY retry on intel_dp_aux_ch.

["Thulasimani, Sivakumar" <sivakumar.thulasimani@intel.com>]

On 10/21/2015 7:54 PM, Vivi, Rodrigo wrote:
> On Wed, 2015-10-21 at 12:19 +0300, Ville Syrjälä wrote:
>> On Wed, Oct 21, 2015 at 10:28:51AM -0700, Rodrigo Vivi wrote:
>>> EBUSY retries are already in place at drm level.
>>> We don't need to replicate the job here.
>>>
>>> Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
>>> ---
>>>   drivers/gpu/drm/i915/intel_dp.c | 20 ++------------------
>>>   1 file changed, 2 insertions(+), 18 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/intel_dp.c
>>> b/drivers/gpu/drm/i915/intel_dp.c
>>> index 09bdd94..d054129 100644
>>> --- a/drivers/gpu/drm/i915/intel_dp.c
>>> +++ b/drivers/gpu/drm/i915/intel_dp.c
>>> @@ -818,24 +818,8 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
>>>   
>>>   	intel_aux_display_runtime_get(dev_priv);
>>>   
>>> -	/* Try to wait for any previous AUX channel activity */
>>> -	for (try = 0; try < 3; try++) {
>>> -		status = I915_READ_NOTRACE(ch_ctl);
>>> -		if ((status & DP_AUX_CH_CTL_SEND_BUSY) == 0)
>>> -			break;
>>> -		msleep(1);
>> The dp helper doesn't sleep at all between the retries, so dropping
>> the
>> sleep from here may change the behaviour.
> hm indeed... what about
> + msleep(1);
> + ret = -EBUSY
> + goto out;
> ?
the current code is one of few test cases that pass during compliance 
testing
so please confirm this change does not break that :).

regards,
Sivakumar
>>> -	}
>>> -
>>> -	if (try == 3) {
>>> -		static u32 last_status = -1;
>>> -		const u32 status = I915_READ(ch_ctl);
>>> -
>>> -		if (status != last_status) {
>>> -			WARN(1, "dp_aux_ch not started status
>>> 0x%08x\n",
>>> -			     status);
>>> -			last_status = status;
>>> -		}
>>> -
>>> +	status = I915_READ_NOTRACE(ch_ctl);
>>> +	if ((status & DP_AUX_CH_CTL_SEND_BUSY) != 0) {
>>>   		ret = -EBUSY;
>>>   		goto out;
>>>   	}
>>> -- 
>>> 2.4.3
>>>
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