Re: [Intel-gfx] [PATCH] drm/dp: add module parameter for the dpcd access max retries

From: Jani Nikula <jani.nikula@linux.intel.com>
Cc: feng.tang@intel.com, David Airlie <airlied@linux.ie>,
	intel-gfx <intel-gfx@lists.freedesktop.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	fei.jiang@intel.com
Subject: Re: [Intel-gfx] [PATCH] drm/dp: add module parameter for the dpcd access max retries
Date: Wed, 09 May 2018 12:28:15 +0300	[thread overview]
Message-ID: <87h8nh41qo.fsf@intel.com> (raw)
In-Reply-To: <20180509075651.cyno666vhmixela6@shbuild888>

On Wed, 09 May 2018, Feng Tang <feng.tang@intel.com> wrote:
> On Wed, May 09, 2018 at 10:53:53AM +0300, Jani Nikula wrote:
>> On Wed, 09 May 2018, Feng Tang <feng.tang@intel.com> wrote:
>> > On Tue, May 08, 2018 at 10:30:19PM +0300, Jani Nikula wrote:
>> >> On Wed, 09 May 2018, Feng Tang <feng.tang@intel.com> wrote:
>> >> >> Well if it's edp probing, then atm we do need to block since we have
>> >> >> no support for panel hotplugging. And userspace generally no
>> >> >> expectations that built-in panels come&go. async_synchronize_full
>> >> >> making our fbdev code less async than desired is kinda a different
>> >> >> story I think here. First step would be trying to figure out why we
>> >> >> even bother with edp probing on this platform, when the thing isn't
>> >> >> there. Sounds like broken VBT.
>> >> >
>> >> > Hi Daniel,
>> >> >
>> >> > Here are some of the VBT and DPCD related logs on my A3900 (bxt + GEN9 LP)
>> >> > based NUC. but I don't have the knowledge to tell if the VBT is broken :)
>> >> 
>> >> Please run current upstream drm-tip when you're suggesting changes to
>> >> upstream code. Looks like you're running at most v4.14. This can't be
>> >> emphasized enough. We can't and won't merge the changes unless they make
>> >> sense with current code.
>> >
>> > Yes, I understand, the patch posted  was created right after git-pulling
>> > Linus' tree, and back-ported to test with 4.14 kernel. 
>> >
>> >> 
>> >> As to vbt, please send me /sys/kernel/debug/dri/0/i915_vbt.
>> >
>> > Sure. as attached
>> 
>> Your VBT claims the device has an eDP panel. Does it have one or not?
>
> After asking around, our platform (BXT NUC) does have a eDP interface (someone
> has tested with a eDP screen), but most of our platforms are connected
> with 2 HDMI LCD monitors.

Sounds like you should have a different VBT for the cases where you ship
with/without eDP connected. As you've noticed, we generally try pretty
hard to talk to the panel if VBT says it's there, to avoid black screens
which are a much worse scenario than delays in detection.

BR,
Jani.

>
> Thanks,
> Feng

-- 
Jani Nikula, Intel Open Source Technology Center
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