From: Clemens Ladisch <clemens@la...> - 2009-10-28 09:51:17
what should the pixclock field for the FBIOPUT_VSCREENINFO ioctl be set
to when an application doesn't care about the timing?
The fbset tool and Xorg's fbdevhw driver set it to zero when they have
no timing. Other programs (like links or xine) set it to the value
returned by FBIOGET_VSCREENINFO.
However, this seems to be different from the actual DRM helpers
drm_fb_helper_single_fb_probe() initializes pixclock to -1, and this is
the value returned by FBIOGET_VSCREENINFO. (Many programs treat this
as a valid value, 0xffffffff = 4 ms.)
drm_fb_helper_check_var() explicitly rejects both values, 0 or -1.
drm_fb_helper_set_par() refuses to work with any value except -1.