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SubjectRe: i915/kms/backlight-combo mode problem
Forward to upstream for more discussion.

於 五,2011-05-13 於 17:27 +0800,Michael Chang 提到:
> Melchior,
>
> I tried to puzzle out the possible cause of the problem, but sorry
> that no further progress to give you. I'd like to debug this issue,
> also did Joey. But there's more questions in my mind, made me feel not
> able to proceed any further.. :(
>
> 1. is_backlight_combination_mode() really returns 0x4 ..? I understand
> your words, but if this is true then Joey Lee provided patch should
> log out some information about changing the LPBC
>
> set backlight lbpc = ...
>
> but I didn't see any of the log output .. :(
>
> 2. I dig the old mailing thread .. found a post
>
> http://marc.info/?l=linux-kernel&m=130462815211684&w=2
>
> If you rebase this patch to your currently git commit, will it fixes
> all problems for you now (only vanilla kernel with this patch)? (You
> replied that this patch works for you ..) Also another interesting
> finding...
>
> > + if (!lbpc)
> > + combo_mode = 0;
>
> Looks like the purpose of it is to NOT touch the LPBC registers if
> lbpc is zero ...(since this forces is_backlight_combination_mode
> return 0). This would make contradiction about the assumption that you
> could change to back-light via LPBC .. (using setpci is actually
> access the LPBC registers .. IMHO).
>
> Total a mess for me now .. Did I made anything wrong .. I know I may
> lose some details.
>
> I'm thinking is it ok for us to discuss in IRC, the communication
> would be more efficient. Would this be convenient for you ? This is up
> to you.
>
> Have nice weekend .. :)
>
> Regards,
> Michael Chang
>
> 2011/5/10 Melchior FRANZ <melchior.franz@gmail.com>:
> > * Michael Chang -- Tuesday 10 May 2011:
> >> Could you please try this patch and get the log ? We wonder why
> >> is_backlight_combination_mode () returns false.
> >
> > This information was already buried in the bugzilla thread:
> >
> > https://bugzilla.kernel.org/show_bug.cgi?id=31522
> > "It turned out that on this machine INTEL_INFO(dev)->gen equals 4,
> > and is_backlight_combination_mode() returns 0x40000000."
> >
> >
> > But to say it again in your words: :-)
> >
> > [drm:is_backlight_combination_mode], BLM_COMBINATION_MODE = 1073741824 (0x40000000)
> >
> > 6x during boot-up, and several times later when changing the backlight
> > brightness.
> >
> >
> > This was with 8b061610dac3a3b89770c85ad63b481a47b0c38e. And now
> > I have a little shocker for you (and me): because this was a
> > vanilla kernel (apart from these debug messages), the screen went
> > black again, like I knew it. But pressing the "brightness down"
> > key turns the backlight on! I can't believe that I haven't tested
> > that. I guess I've only tried "brightness up" and "display toggle".
> > Those don't turn backlight on. Or maybe somethine else relevant
> > meanwhile changed in the i915 drivers. (I've regularly been
> > updating to HEAD.)
> >
> > So, the problem was just the initial state all the time?
> >
> > m.
> >


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