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    SubjectRe: [PATCH] drm_fb_helper: fix regression in pixclock check
    Clemens Ladisch wrote:
    > Jason Wessel wrote:
    >> Commit 5349ef3127c77075ff70b2014f17ae0fbcaaf199 changed pixclock to be
    >> initialized to zero instead of -1.
    > Zero meaning "there is no pixel clock value". When I wrote the patch,
    > the FB (helper) code did not use this value at all, so zero was the only
    > value that could possibly be used.
    >> The validation routine always returns -EINVAL for a valid pixclock
    > It declares that the only valid pixclock value is "none". This was
    > required to make the userspace API work, since the GET ioctls return
    > this value, and all programs expect to be able to PUT this value back.
    >> which prevents atomic kernel mode setting from working correctly.
    >> ...
    >> @@ -602,7 +602,7 @@ int drm_fb_helper_check_var(struct fb_var_screeninfo *var,
    >> - if (var->pixclock != 0)
    >> + if (!var->pixclock)
    >> return -EINVAL;
    > This change breaks the userspace API again, unless the other parts of
    > the code have been changed to always return a valid pixclock value when
    > reading the current mode settings.
    > If we want to accept both zero and non-zero values for pixclock, this
    > check should be dropped altogether.
    > In drm_fb_helper_set_par(), there is a corresponding check that must be
    > kept in sync with this one.

    Fair enough. We'll make a special case for when the kernel debugger is

    Looks to me like it worked by luck during the 2.6.32 kernel cycle for
    the atomic kernel mode setting. I have changed it in the next version
    of this patch to always return -EINVAL while the kernel debugger is
    active. This restores the atomic kernel mode setting back to the
    working state, until we can find a better solution.


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      Last update: 2009-12-23 20:07    [W:0.022 / U:12.820 seconds]
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