Re: [Intel-gfx] [PATCH 0/2] drm: link status property and DP link training failure handling

[Jani Nikula <jani.nikula@intel.com>]

On Fri, 20 Jan 2017, Martin Peres <martin.peres@linux.intel.com> wrote:
> On 19/01/17 11:18, Jani Nikula wrote:
>> On Wed, 18 Jan 2017, Martin Peres <martin.peres@linux.intel.com> wrote:
>>> On 16/12/16 15:48, Daniel Vetter wrote:
>>>> On Fri, Dec 16, 2016 at 12:29:05PM +0200, Jani Nikula wrote:
>>>>> The two remaining patches from [1], rebased.
>>>>>
>>>>> BR,
>>>>> Jani.
>>>>>
>>>>>
>>>>> [1] http://mid.mail-archive.com/1480984058-552-1-git-send-email-manasi.d.navare@intel.com
>>>>
>>>> Just for the record, I think the only thing missing here is the Xorg
>>>> review on the -modesetting patch. As soon as we have that I can vacuum
>>>> this up (probably best through drm-misc, but not sure).
>>>
>>> Hey Daniel,
>>>
>>> I tested again on Monday -modesetting with the patch from Jani to inject
>>> faults and did manage to get both the link-status BAD and a lower
>>> resolution got select dynamically when running KDE. For the latter, I
>>> however needed the following patch:
>>> https://patchwork.kernel.org/patch/9491869/
>>>
>>> Now, that being said, Jani's patch just prevents a new modeset to work,
>>> it does not tear down the current mode. This may be the reason why I do
>>> not manage to get a black screen after > 3 failures (and already a
>>> 1024x768 resolution).
>>>
>>> I however need to do more testing when running without a DE (straight X
>>> + twm and xterm). Indeed, when I hotplug my DP screen, it gets to the
>>> native resolution automatically without me asking for it using xrandr.
>>> Also, the mode that is set does not seem to go through
>>> intel_dp_start_link_train (what the heck?), so I do not get any failure
>>> and I cannot induce one :s
>>
>> Huh, does your X + twm actually respond to hotplugs?
>>
>
> No, that was the point of the test :) I just wanted to see the screen 
> turn black but it did not because even if the link training fails, i915 
> keeps on going and pushes the pixels out constantly. My screen was 
> good-enough to pick it up and display it without complaining ... which 
> is really surprising for DP, isn't it?

And this, my friend, is why we plunge on in spite of errors, instead of
failing fast and bailing out. If you were a normal user, you'd
*appreciate* not having a black screen! ;)

BR,
Jani.

-- 
Jani Nikula, Intel Open Source Technology Center
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