Messages in this thread | | | Subject | Re: [PATCH V3 13/18] coresight: tmc: make sysFS and Perf mode mutually exclusive | From | Suzuki K Poulose <> | Date | Tue, 26 Apr 2016 10:23:20 +0100 |
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On 25/04/16 16:18, Mathieu Poirier wrote: > On 25 April 2016 at 09:11, Suzuki K Poulose <Suzuki.Poulose@arm.com> wrote: >> On 25/04/16 16:05, Mathieu Poirier wrote: >>> >>> On 25 April 2016 at 08:52, Suzuki K Poulose <Suzuki.Poulose@arm.com> >>> wrote: >>>> >>>> On 25/04/16 15:48, Mathieu Poirier wrote: >>>>> >>>>> >>>>> On 25 April 2016 at 08:32, Suzuki K Poulose <Suzuki.Poulose@arm.com> >>>>> wrote: >>>>>> >>>>>> >>>>>> On 22/04/16 18:14, Mathieu Poirier wrote: >>>> >>>> >>>> >>>>>>> + spin_lock_irqsave(&drvdata->spinlock, flags); >>>>>>> + if (drvdata->reading) { >>>>>>> + ret = -EINVAL; >>>>>>> + goto out; >>>>>>> + } >>>>>>> + >>>>>>> + val = local_xchg(&drvdata->mode, mode); >>>>>>> + /* >>>>>>> + * In Perf mode there can be only one writer per sink. There >>>>>>> + * is also no need to continue if the ETR is already operated >>>>>>> + * from sysFS. >>>>>>> + */ >>>>>>> + if (val != CS_MODE_DISABLED) { >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> Could val be CS_MODE_PERF ? In other words, should we be checking : >>>>>> if (val == CS_MODE_SYSFS) instead ? >>>>> >>>>> >>>>> >>>>> If we check for CS_MODE_SYSFS we also have to check for CS_MODE_PERF, >>>>> which is two checks rather than a single one with the current >>>>> solution. >>>> >>>> >>>> >>>> I am confused now. The comment says, we want to check for sysfs mode and >>>> don't continue in that case. So, we shouldn't be worried about PERF mode. >>> >>> >>> You are correct about the sysFS part, but the first sentence of the >>> comment also mention that in perf mode there can only be one writer >>> per sink. Otherwise ring buffers for one session would end up with >>> traces from other ongoing sessions, and that is not taking into >>> account the buffer management nightmares it would cause. >> >> >> OK, in either case, val == CS_MODE_SYSFS is much better check there, to >> what we want to do > > If we check for SYSFS we also need to check for PERF. Otherwise > nothing prevents another session from using the sink buffer, which is > not supported.
Ah, I got wrong. Sorry for the noise. The current check makes sense.
Suzuki
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