W dniu 22.04.2024 o 16:18, Peter Maydell pisze:
On Mon, 22 Apr 2024 at 14:38, Marcin Juszkiewicz
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"
Yeah, it looks like it's TF-A that hardcodes the frequency:
https://github.com/ARM-software/arm-trusted-firmware/blob/c8be7c08c3b3a2330d54b58651faa9438ff34f6e/plat/qemu/qemu_sbsa/include/platform_def.h#L269
I imagine that value gets written into CNTFRQ by TF-A somewhere
along the line (and then read by EDK2 later), though I haven't
quite found where. Plus I notice that the TF-A sbsa-watchdog-timer
assumes that the generic-timer frequency and the watchdog
timer frequency are the same, which is a bit dubious IMHO.
It also seems to be hardcoded in TF-A's support for the virt
board too, annoyingly.
I looked at it and it seems that TF-A can just read what is in
CNTFRQ_EL0 instead of hardcoding the value.
Submitted patch:
https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/28313
refactor(qemu): do not hardcode counter frequency [NEW]
