linux-kernel - Re: [PATCH v2] drm/radeon: Retry DDC probing on DVI on failure if we got an HPD interrupt

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Date:	Fri, 4 Dec 2015 10:54:34 +0100
From:	Christian König <christian.koenig@....com>
To:	Boszormenyi Zoltan <zboszor@...hu>, <cpaul@...hat.com>,
	Alex Deucher <alexander.deucher@....com>,
	David Airlie <airlied@...ux.ie>,
	<dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
CC:	Jerome Glisse <jglisse@...hat.com>,
	Benjamin Tissoires <benjamin.tissoires@...hat.com>
Subject: Re: [PATCH v2] drm/radeon: Retry DDC probing on DVI on failure if we
 got an HPD interrupt

On 04.12.2015 10:43, Boszormenyi Zoltan wrote:
> 2015-12-04 09:53 keltezéssel, Christian König írta:
>> On 04.12.2015 00:26, cpaul@...hat.com wrote:
>>> From: Lyude <cpaul@...hat.com>
>>>
>>> HPD signals on DVI ports can be fired off before the pins required for
>>> DDC probing actually make contact, due to the pins for HPD making
>>> contact first. This results in a HPD signal being asserted but DDC
>>> probing failing, resulting in hotplugging occasionally failing.
>>>
>>> This is somewhat rare on most cards (depending on what angle you plug
>>> the DVI connector in), but on some cards it happens constantly. The
>>> Radeon R5 on the machine used for testing this patch for instance, runs
>>> into this issue just about every time I try to hotplug a DVI monitor and
>>> as a result hotplugging almost never works.
>>>
>>> Rescheduling the hotplug work for a second when we run into an HPD
>>> signal with a failing DDC probe usually gives enough time for the rest
>>> of the connector's pins to make contact, and fixes this issue.
>>>
>>> Signed-off-by: Lyude <cpaul@...hat.com>
>> I find a second a bit long, but if it works so what?
>>
>> Looks sane enough to me, patch is Reviewed-by: Christian König <christian.koenig@....com>
> Does this patch help in case of the Radeon chip only has HDMI and DP outputs
> exposed (Zotac ZBOXNANO-AQ01) but used with DVI or VGA monitors with
> converter cables? We have some problems with such scenarios that sounds
> eerily similar to this description.

No, at least active converter cables are a completely different case.

Regards,
Christian.

>
> Inquiry-by: Zoltán Böszörményi <zboszor@...hu>
> ;-)
>
> Thanks in advance.
>

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