Re: [edk2-devel] [edk2-staging/RiscV64QemuVirt PATCH 25/29] OvmfPkg: Add NorFlashQemuLib library

["Ard Biesheuvel" <ardb@kernel.org>]

On Wed, 19 Oct 2022 at 15:06, Sami Mujawar <sami.mujawar@arm.com> wrote:
>
> Hi Ard,
>
> Please see my query inline marked [SAMI].
>
> Regards,
>
> Sami Mujawar
>
> On 19/10/2022 01:19 pm, Ard Biesheuvel via groups.io wrote:
> > On Mon, 10 Oct 2022 at 12:13, Sunil V L <sunilvl@ventanamicro.com> wrote:
> >> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4076
> >>
> >> This is copied from ArmVirtPkg since it is required for
> >> other architectures also.
> >>
> >> It also adds the instance for single flash drive which has
> >> both code and variables. This is copied from SbsaQemu.
> >>
> >> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
> >> Cc: Jiewen Yao <jiewen.yao@intel.com>
> >> Cc: Jordan Justen <jordan.l.justen@intel.com>
> >> Cc: Gerd Hoffmann <kraxel@redhat.com>
> >> Cc: Daniel Schaefer <git@danielschaefer.me>
> >> Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
> > Let's call these
> >
> > QemuNorFlashPlatformLib [for the library class]
> >
> > QemuNorFlashDeviceTreeLib
> > QemuNorFlashStaticLib
> >
> > and for the driver
> >
> > QemuNorFlashDxe
>
> [SAMI] We use the NorFlashDxe for the Kvmtool guest firmware, see
> https://github.com/tianocore/edk2/blob/master/ArmVirtPkg/ArmVirtKvmTool.dsc#L294
>
> Considering this, should QemuNorFlashDxe be called OvmfNorFlashDxe?
>
> [/SAMI]
>

Ah yes, good point. So using Qemu as a prefix is slightly problematic.

My intent is for this driver to be optimized towards NOR flash
emulation the way QEMU implements it. The main difference between the
platforms is that some of them (notably, ArmVirtQemu.dsc) also execute
from the emulated region, which requires an executable (read-only)
memslot in KVM, as instruction fetches (as opposed to explicit loads
and stores) cannot be emulated by KVM. KvmTool only uses the NOR flash
for variables, so it doesn't really care how the emulation is
implemented, as long as the loads and stores are carried out in the
expected way.

I don't think the Ovmf prefix makes sense here either - OVMF is still
primarily x86, which uses a different flash emulation altogether.
Maybe VirtNorFlashDxe, to emphasize that it does not expect to be
dealing with actual NOR flash?

Suggestions welcome :-)