On Tue, 22 Mar 2022 at 06:42, Chan Kim <c...@etri.re.kr> wrote: > > Hi, > > It may not be important but I'm trying to make the linux boot log the same > for qemu direct kernel loading and loading by u-boot. > In armv8 the cntfrq_el0 register is supposed to be written with the system > counter frequency. The armv8 manual says it doesn't affect the hardware > operation and it's just for S/W to know the frequency. U-boot program writes > to that register with COUNTER_FREQUENCY value, when it's defined. In current > armv8 virt machine, it's read as 62.5MHz but I coulnd't find where in the > source the value is written. Where should I change to value in the qemu > source?
If you want to model a board with a different CNTFRQ frequency you should set the "cntfrq" property on the CPU object(s), which will then cause the reset CNTFRQ_EL0 to be set accordingly, and more importantly will mean the CPU generic timers actually run at that frequency. hw/arm/aspeed_ast2600.c is an example SoC that does this. (QEMU provides a reset value for this register for when it's directly booting a kernel -- in real hardware the firmware is supposed to set the value, but when QEMU direct-boots a kernel it's QEMU that's doing some of the jobs firmware would do.) -- PMM
