iMX53 PMU returns no data

[Paweł Moll]

Board: Quickstart
Build: https://android-build.linaro.org/builds/~linaro-android/staging-imx53-11.11-release/#build=2
Kernel:

We tried DS-5 Streamline on that build (https://wiki.linaro.org/Platform/DevPlatform/DS5) and observed a problem known long time ago on OMAP3 - all values read from the PMU's performance counters (except for the cycle counter) are always 0. Cortex-A8 PMU behaviour depends on the DBGEN signal state (see http://infocenter.arm.com/help/topic/com.arm.doc.ddi0344k/Bgbhjhjd.html). The way this signal is controlled depends on the SoC implementation and my guess is that it is disabled by default in iMX53 (as it was on OMAP3). TI people are initializing the debug/PMU subsystem when CONFIG_OMAP3_EMU=y.

I was trying to confirm the behaviour using perf, but it explodes because of other reasons (see https://bugs.launchpad.net/bugs/893653).

[Paweł Moll (pawel-moll)]

The same observed on the latest staging build 77 (https://android-build.linaro.org/builds/~linaro-android/staging-imx53/)

Linux version 3.1.0-rc9+ (jenkins-build@ip-10-191-7-147) (gcc version 4.6.2 (Linaro GCC 4.6-2011.11)) 1 PREEMPT Tue Nov 22 12:06:20 UTC 2011

[Paweł Moll (pawel-moll)]

Now confirmed with perf. The "instructions" and "bus-cycles" _must_ return more then 0... As you can see "cpu-cycles" is fine (> 0), which is consistent with PMU behaviour when DBGEN=0.

$ uname -a
Linux vespa 3.1.0-1002-linaro-lt-mx5 #10-Ubuntu PREEMPT Wed Nov 30 03:53:54 UTC 2011 armv7l armv7l armv7l GNU/Linux
$ perf stat -e cpu-cycles sleep 5

 Performance counter stats for 'sleep 5':

           7065432 cpu-cycles # 0.000 GHz

       5.015477242 seconds time elapsed

$ perf stat -e instructions sleep 5

 Performance counter stats for 'sleep 5':

                 0 instructions # 0.00 insns per cycle

       5.016311437 seconds time elapsed

$ perf stat -e bus-cycles sleep 5

 Performance counter stats for 'sleep 5':

                 0 bus-cycles

       5.016281238 seconds time elapsed

[Eric Miao (eric.y.miao)]

The PMU issue has been fixed on the ubuntu side. The Android kernel needs to be rebased against latest lt-3.1 branch. Move this to next month's milestone.

[Fathi Boudra (fboudra)]

Set to fix-released for linaro-ubuntu, according to Eric comment #3 and confirmed on IRC.

[Milosz Wasilewski (mwasilew)]

iMX53 is no longer supported.