Re: [PATCH 4/4] drm/i915: Retry for live status

["Sharma, Shashank" <shashank.sharma@intel.com>]

Regards
Shashank

On 8/26/2015 8:47 PM, Daniel Vetter wrote:
> On Wed, Aug 26, 2015 at 10:05:00AM +0000, Jindal, Sonika wrote:
>> HPD bits control the interrupt but the live status (with some monitors) takes time to get set.
>> We had experienced this with VLV and CHV with few monitors.
>> So Android code always has this retry for live status.
>>
>> Yes, this was not added in the previous series because we planned to add the next set of optimization a little while later.
>> But this seems to be an important one.
>>
>> It will be great if you can try it with your ivb. But for that you would need to first change the gen check and add a call to check live status for ivb.
>
> Done (well I just quickly hacked up the same idea on top of your old
> patches). Lessons to be learned from this:
> - Make sure that you really include _all_ the bugfixes. This pach here
>    isn't just tuning, it's crucial to make it work. And this isn't the
>    first time vpg teams upstream something and later on we notice that
>    important bugfixes have been forgotten.
>
>    Because this wasn't done both you & me wasted a lot of time arguing
>    about these patches and trying to test them.
>
Agree. We thought once the basic optimization goes in, we will add this 
as fine tuning patch. We were afraid of you guys doubting this approach 
at first itself. It looks like a little hack, but the HW itself is 
screwed up like this, to deal with.
> - Please squash this patch in with patch 3 since otherwise we have a
>    regression. Also please try to dig out why exactly this works like this
>    since the hpd irq happening _before_ hpd status settles sounds to me
>    like we have a little time machine in our silicon which can predict the
>    future ...
>
Actually this depends on the monitor also. Few monitors are slow to 
assert the HPD line, or sometimes they don't provide the right voltage 
on that, causing live status to fluctuate for a while. While VLV/CHV 
beta testing we have done this experiment with a big range of monitors, 
and concluded that 30ms(retry of 10ms * 3) is the optimized time where 
most of the monitors respond well.

We saw that we cant delay further, because HDCP compliance expects us to 
respond to HPD (out) with in 100ms. So after careful testing with many 
monitors, we have concluded this range.
> - Please respin the patch series with the IS_VLV || gen >= 8 checks drop,
>    I'm fairly confident that this bugfix here is the bit we've been looking
>    for since years. At least it would be good to retest on all platforms
>    for maximal test coverage.
>
Sure. Will do that.
> Cheers, Daniel
>>
>> Regards,
>> Sonika
>> -----Original Message-----
>> From: Daniel Vetter [mailto:daniel.vetter@ffwll.ch] On Behalf Of Daniel Vetter
>> Sent: Wednesday, August 26, 2015 3:10 PM
>> To: Jindal, Sonika
>> Cc: intel-gfx@lists.freedesktop.org
>> Subject: Re: [Intel-gfx] [PATCH 4/4] drm/i915: Retry for live status
>>
>> On Tue, Aug 25, 2015 at 05:31:33PM +0530, Sonika Jindal wrote:
>>> Some monitors take time in setting the live status.
>>> So retry for few times if this is a connect HPD
>>>
>>> Signed-off-by: Sonika Jindal <sonika.jindal@intel.com>
>>
>> Why was this bugfix not part of the original series? Now I have to retest on my ivb to figure out whether maybe this one here is the issue ...
>>
>> Also how exactly does this work? I thought the hpd bits control whether we get an interrupt, not the other way round? Why exactly does this help?
>> Definitely needs a lot more explanation.
>>
>> Also this seems to break bisect, since before the preceeding patch to check hpd status we just retried edid reading for a while.
>>
>> This kind of hacking doesn't really convince me that hpd status is working, just that our own testing isn't good enough to catch all real-world issues.
>> -Daniel
>>
>>> ---
>>>   drivers/gpu/drm/i915/intel_hdmi.c |   15 +++++++++++++++
>>>   1 file changed, 15 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/i915/intel_hdmi.c
>>> b/drivers/gpu/drm/i915/intel_hdmi.c
>>> index 59518b4..239d70d 100644
>>> --- a/drivers/gpu/drm/i915/intel_hdmi.c
>>> +++ b/drivers/gpu/drm/i915/intel_hdmi.c
>>> @@ -1415,6 +1415,7 @@ void intel_hdmi_probe(struct intel_encoder *intel_encoder)
>>>   	struct intel_connector *intel_connector =
>>>   				intel_hdmi->attached_connector;
>>>   	bool live_status = false;
>>> +	unsigned int retry = 3;
>>>
>>>   	/*
>>>   	 * Sometimes DDI ports are enumerated as DP as well as HDMI and @@
>>> -1425,6 +1426,20 @@ void intel_hdmi_probe(struct intel_encoder *intel_encoder)
>>>   		return;
>>>
>>>   	live_status = intel_hdmi_live_status(hdmi_to_dig_port(intel_hdmi));
>>> +	if (!intel_connector->detect_edid && live_status == false) {
>>> +		/*
>>> +		 * Hotplug had occurred and old status was disconnected,
>>> +		 * so it might be possible that live status is not set,
>>> +		 * so retry for few times
>>> +		 */
>>> +		do {
>>> +			mdelay(10);
>>> +			live_status = intel_hdmi_live_status(hdmi_to_dig_port(intel_hdmi));
>>> +			if (live_status)
>>> +				break;
>>> +		} while (retry--);
>>> +	}
>>> +
>>>   	/*
>>>   	 * We are here, means there is a hotplug or a force
>>>   	 * detection. Clear the cached EDID and probe the
>>> --
>>> 1.7.10.4
>>>
>>> _______________________________________________
>>> Intel-gfx mailing list
>>> Intel-gfx@lists.freedesktop.org
>>> http://lists.freedesktop.org/mailman/listinfo/intel-gfx
>>
>> --
>> Daniel Vetter
>> Software Engineer, Intel Corporation
>> http://blog.ffwll.ch
>
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