On Mon, 22 Oct 2012 12:44:18 +0200, Daniel Vetter <daniel.vetter at ffwll.ch> wrote: > The overlay on the i830M has a peculiar failure mode: It works the > first time around after boot-up, but consistenly hangs the second time > it's used. > > Chris Wilson has dug out a nice errata: > > "1.5.12 Clock Gating Disable for Display Register > Address Offset: 06200h???06203h > > "Bit 3 > Ovrunit Clock Gating Disable. > 0 = Clock gating controlled by unit enabling logic > 1 = Disable clock gating function > DevALM Errata ALM049: Overlay Clock Gating Must be Disabled: Overlay > & L2 Cache clock gating must be disabled in order to prevent device > hangs when turning off overlay.SW must turn off Ovrunit clock gating > (6200h) and L2 Cache clock gating (C8h)." > > Now I've nowhere found that 0xc8 register and hence couldn't apply the > l2 cache workaround. But I've remembered that part of the magic that > the OVERLAY_ON/OFF commands are supposed to do is to rearrange cache > allocations so that the overlay scaler has some scratch space. > > And while pondering how that could explain the hang the 2nd time we > enable the overlay, I've remembered that the old ums overlay code did > _not_ issue the OVERLAY_OFF cmd. > > And indeed, disabling the OFF cmd results in the overlay working > flawlessly, so I guess we can workaround the lack of the above > workaround by simply never disabling the overlay engine once it's > enabled. > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=47827 > Cc: stable at vger.kernel.org > Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch> That looks fun, and indeed will probably work. So if we never issue the OFF command, do we still need i830_init_clock_gating()? And if we do still need i830_init_clock_gating() wouldn't it be better applied as a quirk to intel_overlay_on()? -Chris -- Chris Wilson, Intel Open Source Technology Centre
