On Wed, 18 Aug 2010 20:46:37 +0200, Maciej Rutecki maciej.rutecki@gmail.com wrote:

Last known good: 2.6.35 Failing kernel: 2.6.36-rc1

During boot kernel display this message: [ 0.831906] [drm:intel_calculate_wm] *ERROR* Insufficient FIFO for plane, expect flickering: entries required = 36, available = 28.

To be honest, I was shocked at how often we were actually computing that we required a larger FIFO for scanout than was available. Typically, it is the result of the pessimistic latency we guess for the memory fetch and so we err on the side of extreme caution when computing the watermark. So in effect, we have been clamping the FIFO since the beginning, but we only just added the warning message as an aide to diagnosing some FIFO underruns. We could tone down the error message, the real goal though is to improve the accuracy of the calculation and thereby reduce power.

Systems seems work OK, but in 2.6.35 I don't have this message. On another system with 2.6.36-rc1 kernel I have the same message.

Yes, there was just a couple of places where we changed the calculation to round-up but otherwise the wm logic remained mostly the same. So if you haven't been experiencing FIFO underruns, e.g. the screen flickering, then it is likely that the error is benign (and just wasting power).