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drm/i915: Fix up fifo underrun tracking, take N
So apparently this is tricky. We need to consider: - We start out with all the hw enabling bits disabled, both the individual fifo underrun interrupts and the shared display error interrupts masked. Otherwise if the bios config is broken we'll blow up with a NULL deref in our interrupt handler since the crtc structures aren't set up yet at driver load time. - On gmch we need to mask fifo underruns on the sw side, so always need to set that in sanitize_crtc for those platforms. - On other platforms we try to set the sw tracking so that it reflects the real state. But since a few platforms have shared bits we must _not_ disable fifo underrun reporting. Otherwise we'll never enable the shared error interrupt. This is the state before out patch, but unfortunately this is not good enough. But after a suspend resume operation this is broken: 1. We don't enable the hw interrupts since the same code runs on resume as on driver load. 2. The fifo underrun state adjustments we do in sanitize_crtc doesn't fire on resume since (except for hilarious firmware) all pipes are off at that point. But they also don't hurt since the subsequent crtc enabling due to force_restore will enable fifo underruns. Which means when we enable fifo underrun reporting we notice that the per-crtc state is already correct and short-circuit everthing out. And the interrupt doesn't get enabled. A similar problem would happen if the bios doesn't light up anything when the driver loads. Which is exactly what happens when we reload the driver since our unload functions disables all outputs. Now we can't just rip out the short-circuit logic and unconditionally update the fifo underrun reporting interrupt masking: We have some checks for shared error interrupts to catch issues that happened when the shared error interrupt was disabled. The right fix is to push down this logic so that we can always update the hardware state, but only check for missed fifo underruns on a real enabled->disabled transition and ignore them when we're already disabled. On platforms with shared error interrupt the pipe CRC interrupts are grouped together with the fifo underrun reporting this fixes pipe CRC support after suspend and driver reloads. Testcase: igt/kms_pipe_crc_basic/suspend-* Reviewed-by:Ville Syrjälä <ville.syrjala@linux.intel.com> Signed-off-by: