[RFC PATCH xserver] modesetting: re-set the crtc's mode when link-status goes BAD

[Jani Nikula]

On Tue, 31 Jan 2017, Manasi Navare <manasi.d.navare at intel.com> wrote:
> On Thu, Jan 26, 2017 at 06:21:20PM +0100, Daniel Vetter wrote:
>> On Thu, Jan 26, 2017 at 02:37:28PM +0200, Martin Peres wrote:
>> > Despite all the careful planing of the kernel, a link may become
>> > insufficient to handle the currently-set mode. At this point, the
>> > kernel should mark this particular configuration as being broken
>> > and potentially prune the mode before setting the offending connector's
>> > link-status to BAD and send the userspace a hotplug event. This may
>> > happen right after a modeset or later on.
>> > 
>> > When available, we should use the link-status information to reset
>> > the wanted mode.
>> > 
>> > Signed-off-by: Martin Peres <martin.peres at linux.intel.com>
>> > ---
>> > 
>> > WARNING: The patches have not been merged in the kernel yet, so this patch is
>> > merely an RFC.
>> 
>> That's how it's supposed to happen, before we can merge the kernel side,
>> we need acceptance (=reviewed) by the userspace side. Which is why this
>> patch here.
>> -Daniel
>>
>
> This has been validated with a compliance device inducing a forced link
> failure during modeset, after which the kernel sets the link-status to BAD
> and sends a hotplug to userspace. The -modesetting driver then resets the
> configuration by forcing another mdoeset and retraining the link at lower
> link rate/lane count. This has been proven to pass DP compliance.
> It has been also verified that this avoids the black screens in case of such
> mode failures due to link training failure.

Validation is great, but review is what is required and we're after!

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Technology Center