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 18:05, Sunil V L <sunilvl@ventanamicro.com> wrote:
>
> On Mon, Oct 10, 2022 at 05:29:15PM +0200, Ard Biesheuvel wrote:
> > 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.
>
> Great. Let me rework these patches then.
> >
> > But you haven't answered my question regarding how your version was simplified.
> >
>
> Oh sorry. I forgot to modify the commit message but what I really meant
> was removing the code which depends upon PcdNorFlashCheckBlockLocked for
> virtual platforms. I thought it is useful only for real platforms and
> qemu doesn't emulate it. Let me know if I am wrong.
> Since the driver is copied for OVMF, I didn't want to add the PCD unnecessarily.
>

What I would like to do is the following:

- move NvVarstoreFormattedLib into MdeModulePkg (as you proposed already)
- create a new NorFlashDxe in Ovmf that is cleaned up, drops the
handling of locked blocks (as you suggest) and minimizes the number of
transitions between array mode and programming mode (i have some
patches i can share as a starting point)
- move ArmPlatformPkg's NorFlashDxe into its only remaining user,
which is is Platform/ARM in edk2-platforms (there are two more users
in edk2-platforms, but both are QEMU based on so they can switch to
the OVMF one)


> > 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.
>
> I was not looking at optimizing it at this point of time.
>

I understand. And yet you are already proposing a different version of
NorFlashDxe, and I don't want to clone the existing NorFlashDxe
without cleaning it up first.