Re: [edk2-staging/RiscV64QemuVirt PATCH 26/29] OvmfPkg: Add generic Qemu NOR flash DXE driver

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

On Mon, 10 Oct 2022 at 17:19, Sunil V L <sunilvl@ventanamicro.com> wrote:
>
> On Mon, Oct 10, 2022 at 12:39:21PM +0200, Ard Biesheuvel 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
> > >
> > > RISC-V needs NorFlashDxe driver for qemu virt machine. The
> > > ArmPlatformPkg has this driver but migrating it to generic
> > > package like MdeModulePkg introduces circular dependencies.
> > > So, add a simplified version of the NorFlashDxe driver in
> > > OvmfPkg.
> > >
> >
> > So what is the difference between this simplified version and the old
> > version? And it is backed in QEMU by the same NOR flash emulation,
> > shouldn't we use this driver for ArmVirtQemu as well?
>
> I agree. If we can break the dependency on EmbeddedPkg due to
> NvVarStoreFormattedLib, then we can migrate to MdeModulePkg and all
> consumers can use the same driver which would be the best solution IMO.
>
> Could you please let me know  why NvVarStoreFormattedLib is added
> in EmbeddedPkg instead of MdePkg or MdeModulePkg? Is it only for
> non-server class platforms? I don't see it doing much so not sure
> its use case.
>

I think that library as well as the definition of
gEdkiiNvVarStoreFormattedGuid should be moved to MdeModulePkg.

Then, we can look at moving NorFlashDxe in there as well.

But you haven't answered my question regarding how your version was simplified.

Note that there is some room for improvement in that driver in
relation to execution under KVM: switching between programming mode
and array mode involves setting up/tearing down the KVM memslot, and
currently, the driver is far from optimized when it comes to
minimizing the number of transitions between read mode and write mode.