On Mon, Jun 03, 2024 at 02:41:32PM +0530, Anshuman Khandual wrote: > On 5/29/24 16:21, Mark Rutland wrote: > > On Fri, Apr 05, 2024 at 08:16:34AM +0530, Anshuman Khandual wrote: > >> + For CPUs with feature Branch Record Buffer Extension (FEAT_BRBE): > >> + > >> + - If the kernel is entered at EL2 and EL1 is present: > >> + > >> + - BRBCR_EL1.CC (bit 3) must be initialised to 0b1. > >> + - BRBCR_EL1.MPRED (bit 4) must be initialised to 0b1. > > > > IIUC this isn't necessary; if the kernel is entered at EL2, it's capable > > of initializing the EL1 regs, and it doesn't look like this silently > > affects something we'd need in the absence of a BRBE driver. > > No, this does not affect anything other than the BRBE driver. Ok. > > AFAICT the __init_el2_brbe() code you add below handles this, so I think > > this is redundant and can be deleted. > > Did not understand the above. __init_el2_brbe() handles setting both BRBCR_EL2 > and BRBCR_EL1 for CC and MPRED config irrespective of whether the kernel enters > EL2 directly or enters EL1 via EL2. But should not that be documented here for > both those scenarios ? OR because once the kernel is in EL2, it can configure > EL1 as required, so it is not a booting requirement anymore ? The latter -- since the kernel can set this up, and only needs to do that for the BRBE driver to work, this doesn't need to be a requiremnt on FW/bootloader. So we can drop this when the kernel is booted at EL2. Mark.
