From: Daniel Vetter Date: Mon, 22 Oct 2012 12:55:55 +0200 Subject: drm/i915: fix overlay on i830M MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit commit a9193983f4f292a82a00c72971c17ec0ee8c6c15 upstream. 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. Note that we have the first part of the above w/a already implemented in i830_init_clock_gating - leave that as-is to avoid surprises. v2: Add a comment in the code. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=47827 Tested-by: Rhys Reviewed-by: Chris Wilson Signed-off-by: Daniel Vetter [bwh: Backported to 3.2: - Adjust context - s/intel_ring_emit(ring, /OUT_RING(/] Signed-off-by: Ben Hutchings --- drivers/gpu/drm/i915/intel_overlay.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) --- a/drivers/gpu/drm/i915/intel_overlay.c +++ b/drivers/gpu/drm/i915/intel_overlay.c @@ -428,9 +428,17 @@ static int intel_overlay_off(struct inte OUT_RING(flip_addr); OUT_RING(MI_WAIT_FOR_EVENT | MI_WAIT_FOR_OVERLAY_FLIP); /* turn overlay off */ - OUT_RING(MI_OVERLAY_FLIP | MI_OVERLAY_OFF); - OUT_RING(flip_addr); - OUT_RING(MI_WAIT_FOR_EVENT | MI_WAIT_FOR_OVERLAY_FLIP); + if (IS_I830(dev)) { + /* Workaround: Don't disable the overlay fully, since otherwise + * it dies on the next OVERLAY_ON cmd. */ + OUT_RING(MI_NOOP); + OUT_RING(MI_NOOP); + OUT_RING(MI_NOOP); + } else { + OUT_RING(MI_OVERLAY_FLIP | MI_OVERLAY_OFF); + OUT_RING(flip_addr); + OUT_RING(MI_WAIT_FOR_EVENT | MI_WAIT_FOR_OVERLAY_FLIP); + } ADVANCE_LP_RING(); return intel_overlay_do_wait_request(overlay, request,