linux-kernel - Re: Linux 3.8-rc4

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Date:	Wed, 30 Jan 2013 14:12:05 -0700
From:	Shuah Khan <shuahkhan@...il.com>
To:	"Deucher, Alexander" <Alexander.Deucher@....com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 3.8-rc4

On Wed, Jan 30, 2013 at 8:53 AM, Deucher, Alexander
<Alexander.Deucher@....com> wrote:
>> -----Original Message-----
>> From: Shuah Khan [mailto:shuahkhan@...il.com]
>> Sent: Wednesday, January 30, 2013 10:35 AM
>> To: Deucher, Alexander
>> Cc: Linus Torvalds; Linux Kernel Mailing List
>> Subject: Re: Linux 3.8-rc4
>>
>> On Wed, Jan 30, 2013 at 6:31 AM, Deucher, Alexander
>> <Alexander.Deucher@....com> wrote:
>>
>> >>
>> >> ok. I did more debugging in rv515_mc_stop() and here is what's
>> >> happening. It has two display controllers and one of them is enabled
>> >> and the other is in disabled state when AVIVO_D1CRTC_CONTROL is
>> >> checked. The current code doesn't blank the disabled crtc. However, it
>> >> needs to be blanked to avoid DMAR faults it appears. I think that is
>> >> what the original code prior to
>> >> 6253e4c75d96006c06b9ac8f417eba873de2497b commit was doing:
>> >>
>> >> -       WREG32(R_0060E8_D1CRTC_UPDATE_LOCK, 1);
>> >> -       WREG32(R_0068E8_D2CRTC_UPDATE_LOCK, 1);
>> >> -       WREG32(R_006080_D1CRTC_CONTROL, 0);
>> >> -       WREG32(R_006880_D2CRTC_CONTROL, 0);
>> >> -       WREG32(R_0060E8_D1CRTC_UPDATE_LOCK, 0);
>> >> -       WREG32(R_0068E8_D2CRTC_UPDATE_LOCK, 0);
>> >> -       WREG32(R_000330_D1VGA_CONTROL, 0);
>> >> -       WREG32(R_000338_D2VGA_CONTROL, 0);
>> >>
>> >> Anyways, here is the diff for the change (by no means a patch) I made
>> >> that fixed the problem:
>> >
>> > Unfortunately, that just fixes the problem by causing an additional delay
>> since the wait_for_vblank() and get_frame_count() loops will timeout since
>> the secondary display is disabled.  The previous code disabled the displays
>> completely while the new code just disables the memory request interface
>> so that the display timing stays on to avoid additional flicker at startup or GPU
>> reset.  For some reason on your system there seems to be a delay in getting
>> the memory request interface to stop.
>> >
>> > Alex
>>
>> Right. That makes sense and yes the annoying flicker went away. :) Can
>> you think of something that can address systems that would need more
>> time to get the memory request interface to stop such as mine?
>
> Does adding an additional radeon_mc_wait_for_idle(rdev) call at the end of rv515_mc_stop() help?  Can you find out what the minimum delay required for your system is?
>
> Alex

Adding radeon_mc_wait_for_idle(rdev) call at the end of
rv515_mc_stop() - didn't help.

I tried with adding udelay() with delay values of 1,10, and 50, and
100 at the end of rv515_mc_stop(). 100 is the minimum that fixed the
DMAR faults.

-- Shuah
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