On Mon, Dec 13, 2021 at 08:57:01PM +0800, Min Xu wrote: > BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3711 > > Discussion in https://bugzilla.tianocore.org/show_bug.cgi?id=1496 shows > that 8254TimerDxe was not written for OVMF. It was moved over from > PcAtChipsetPkg to OvmfPkg in 2019. Probably because OVMF was the only > user left. > > Most likely the reason OVMF used 8254TimerDxe initially was that it could > just use the existing driver in PcAtChipsetPkg. And it simply hasn't > been changed ever. > > CSM support was moved in 2019 too. (CSM support depends on 8254/8259 > drivers). So 8254TimerDxe will be used when CSM_ENABLE=TRUE. > > There are 4 .dsc which include the 8254Timer. > - OvmfPkg/AmdSev/AmdSevX64.dsc > - OvmfPkg/OvmfPkgIa32.dsc > - OvmfPkg/OvmfPkgIa32X64.dsc > - OvmfPkg/OvmfPkgX64.dsc > > For the three OvmfPkg* configs using 8254TimerDxe with CSM_ENABLE=TRUE > and LapicTimerDxe otherwise. > > For the AmdSev config it doesn't make sense to support a CSM. So use > the lapic timer unconditionally. > > Cc: Ard Biesheuvel <ardb+tianoc...@kernel.org> > Cc: Jordan Justen <jordan.l.jus...@intel.com> > Cc: Brijesh Singh <brijesh.si...@amd.com> > Cc: Erdem Aktas <erdemak...@google.com> > Cc: James Bottomley <j...@linux.ibm.com> > Cc: Jiewen Yao <jiewen....@intel.com> > Cc: Tom Lendacky <thomas.lenda...@amd.com> > Cc: Gerd Hoffmann <kra...@redhat.com> > Suggested-by: Gerd Hoffmann <kra...@redhat.com> > Signed-off-by: Min Xu <min.m...@intel.com>
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