Re: Fix For Korg Bug #14897 (GM45 Display Flicker)

[ykzhao]

On Wed, 2010-01-27 at 17:31 +0800, David John wrote:
> Hi Jesse, Yakui,
> 
> Sorry for the delay, but I was busy with other work last week. I got
> some time to look into this on Monday and the problem seems to be this:

Hi, David
	Very good work. Thanks for looking at this issue.
	Do you have an opportunity to try the following patch set on 2.6.33-rc5
kernel and see whether the display flicker issue can be fixed?

>http://lists.freedesktop.org/archives/intel-gfx/2010-January/005505.html	

(The first patch can be skipped as it is already in 2.6.33-rc5 kernel).

Thanks.
	Yakui

> 
> With the external display connected on VGA, intel_update_watermarks
> calls update_wm a couple of times in sequence with the following params:
> 
> 1) planea_clock = 148500 planeb_clock = 0, sr_hdisplay=1920 (VGA)
> 2) planea_clock = 148500 planeb_clock = 72330, sr_hdisplay=1366 (LVDS)
> 
> In update_wm (in my case g4x_update_wm), for 1) sr_entries is calculated
> correctly and self refresh is enabled. For 2) sr_entries remains zero
> and the SR watermark is set as such. However, SR remains
> active. On mode switch to console, this causes a FIFO underrun and the
> display flicker.
> 
> The solution that I see is to simply disable SR if more than one pipe is
> enabled. I've written a patch that does this. Also another point is that
> the G45 docs state that a particular sequence has to be followed if SR
> is to be used when only one pipe is active for Cantiga (Pg 30, G45 Vol
> 3). I didn't see any code doing this, but I did not see any untoward
> behaviour either, with only my patch applied.
> 
> I've updated the patch to fix i965 and i9xx as I assume the same problem
> will occur on those chipsets as well, but this has _not_been tested as I
> don't have the relevant platforms.
> 
> Patch follows this mail. Please let me know if any changes are required.
> 
> The VGA output powering-on on mode change mentioned in my bug report is
> a separate DRM bug for which I will send a patch later.
> 
> Regards,
> David.

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