Created attachment 44567 [details] [review]
The patch to fix this issue

The patch to fix this issue

The patch is incorrect.

You want just:

return mask && (mask & -mask) == mask;

Bad me, forgetting is_pot().

I guess 

mask && (mask & (mask - 1) == 0 and
mask && (mask & -mask) == mask 

is equal. Right?

Oh, right, I did something extra. No need to change ffs to fls as we have only one bit set.

Thanks.

The patch works on huronriver.

I've queued:

commit 84ec542510602575073259e10f52b6e8f1ca94b7
Author: Yuanhan Liu <yuanhan.liu@intel.com>
Date:   Fri Mar 18 07:37:35 2011 +0000

    drm/i915: Re-enable self-refresh
    
    A broken implementation of is_pot() prevented the detection of when a
    singular pipe was enabled.
    
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=35402
    Signed-off-by: Yuanhan Liu <yuanhan.liu@intel.com>
    Tested-by: xunx.fang@intel.com
    Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

commit 7ccb4a53eb03c9196646ca0c2a97558313e886f1
Author: Yuanhan Liu <yuanhan.liu@intel.com>
Date:   Fri Mar 18 07:37:35 2011 +0000

    drm/i915: Re-enable self-refresh
    
    A broken implementation of is_pot() prevented the detection of when a
    singular pipe was enabled. Eric Anholt pointed out the existence of
    is_power_of_2() so use that instead of our broken code!
    
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=35402
    Signed-off-by: Yuanhan Liu <yuanhan.liu@intel.com>
    Tested-by: xunx.fang@intel.com
    Reviewed-by: Keith Packard <keithp@keithp.com>
    Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

Verified with Kernel: (drm-intel-next)caee6066332b83e7f8bdd6f2f40ce46d4836d69c and Kernel: (drm-intel-fixes)2fb4e61d9471867677c97bf11dba8f1e9dfa7f7c.

Closing verified+fixed.