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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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