Re: [PATCH 0/3] target/arm: Make the counter frequency default 1GHz for new CPUs, machines

[Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>]

W dniu 22.04.2024 o 14:56, Peter Maydell pisze:
> On Fri, 19 Apr 2024 at 19:46, Peter Maydell <peter.maydell@linaro.org> wrote:

>> The upshot is that the only CPU type that changes is 'max'; but any
>> new type we add in future (whether v8.6 or not) will also get the new
>> 1GHz default (assuming we spot in code review any attempts to set
>> the ARM_FEATURE_BACKCOMPAT_CNTFRQ flag on new CPU types as a result
>> of cut-n-paste from an older CPU initfn ;-)).
>>
>> It remains the case that the machine model can override the default
>> value via the 'cntfrq' QOM property (regardless of the CPU type).
> 
> This patchset turns out to break the sbsa-ref board: the
> Aarch64SbsarefMachine.test_sbsaref_alpine_linux_max_pauth_impdef
> avocado test both (a) takes rather longer to boot and (b) when
> running thinks that time is advancing very fast.
> 
> I suspect this may be because the firmware hard-codes the
> generic timer clock frequency it is expecting. I've cc'd the
> sbsa-ref maintainers: is that correct?
> 
> If so, we can deal with it by making the sbsa-ref board set the
> cntfrq QOM property on its CPUs to force them to the old
> frequency. However this will produce a technically-out-of-spec
> CPU when used with a v8.6-compliant CPU type, so probably we
> should do something to be able to tell the firmware the clock
> frequency (if it doesn't want to just read CNTFRQ_EL0 itself).

 From what I see in EDK2 code we read CNTFREQ_EL0:

GetPlatformTimerFreq() checks for PcdArmArchTimerFreqInHz variable which
sbsa-ref has set to 0. So it calls ArmGenericTimerGetTimerFreq() ->
ArmReadCntFrq() -> "mrs x0, cntfrq_el0"

I added debug output to firmware and it shows me:

HRW: GetPlatformTimerFreq TimerFreq = 62500000

Local tree:
ed0604e99c (HEAD -> test-counter) target/arm: Default to 1GHz cntfrq for 'max' and new CPUs
c0a8c341f5 target/arm: Refactor default generic timer frequency handling
592c01312b hw: Add compat machines for 9.1
62dbe54c24 (tag: v9.0.0-rc4, origin/master, origin/HEAD) Update version for v9.0.0-rc4 release
a12214d1c4 (origin/staging) usb-storage: Fix BlockConf defaults

sbsa-ref with "-cpu max" used. All cpu cores give me same value.