[Intel-gfx] intel_dp_detect redesign

[Daniel Stone]

Hi,
+marcheu

On 26 November 2015 at 10:07, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Wed, Nov 25, 2015 at 05:09:02PM +0530, Thulasimani, Sivakumar wrote:
>> however good to explicitly check for this,
>> following needs to be tested before sending in next patch/merge
>> 1) MST displays verification (Ander's reported on first set of patches)
>> 2) check behavior on sleep - resume (dave&danvet)
>> 3) storm handling needs to be handled as well. (i assume this should be
>> fine,
>>      but good to check explicitly) (danvet)
>>
>
> Yeah the storm mitigation will keep on working. What I'm worried about is
> that polling won't work any more: When a storm happens we disable the hpd
> and switch all affected connectors completely to polling. Polling happens
> through the probe helpers in drm_probe_helper.c, and that code exclusively
> uses ->detect callbacks. Which means if we no longer re-probe in detect
> (since we assume hpd works correctly) then this will break the storm
> handling code.
>
> Simplest fix (but a bit a hack) would be to check whether polling is
> enabled at the top of intel_hdmi_detect and if so execute a full probe.
> And not just return the cached values.
>
> Note that storms are only a concern for HDMI, not DP (somehow DP hw is
> less shit).

Hmm, from what I understand it's a concern on DP as well. Maybe due to
DP->HDMI converters which just pass HPD through? Google's Type-C -> DP
cable crushes all short HPD events - breaking MST short pulses - which
I assume wasn't for no reason:
https://chromium.googlesource.com/chromiumos/platform/ec/+/master/board/dingdong/board.c#27

Cheers,
Daniel