Re: [PATCH v2 1/1] OvmfPkg/QemuFlashFvbServicesRuntimeDxe: refine flash detection

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

On Thu, 1 Jun 2023 at 10:22, Oliver Steffen <osteffen@redhat.com> wrote:
>
> Quoting Gerd Hoffmann (2023-06-01 08:08:03)
> > Flash can be write-protected in qemu (which is usually the case for
> > code).  In case the variable store flash block is configured read-only
> > ovmf wouldn't be able to store EFI variables there, so not setting up
> > fvb in that case (and fallhack to emulation) is the better option.
>
> I like the term "fallhack", I'll keep that in mind for future use >,<
>

+1

Merged as #4461

> > It'll avoid problems later due to flash writes failing.
> >
> > The patch tries to write back the original value read earlier, so flash
> > content doesn't change in case the write succeeds.  But the status we
> > read back after the attempt to write will tell us whenever flash is
> > writable or not.
> >
> > Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> > ---
> >  OvmfPkg/QemuFlashFvbServicesRuntimeDxe/QemuFlash.c | 14 +++++++++++---
> >  1 file changed, 11 insertions(+), 3 deletions(-)
> >
> > diff --git a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/QemuFlash.c b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/QemuFlash.c
> > index 54f859de9ff9..a577aea55614 100644
> > --- a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/QemuFlash.c
> > +++ b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/QemuFlash.c
> > @@ -114,9 +114,17 @@ QemuFlashDetected (
> >        DEBUG ((DEBUG_INFO, "QemuFlashDetected => FD behaves as RAM\n"));
> >        *Ptr = OriginalUint8;
> >      } else if (ProbeUint8 == CLEARED_ARRAY_STATUS) {
> > -      DEBUG ((DEBUG_INFO, "QemuFlashDetected => FD behaves as FLASH\n"));
> > -      FlashDetected = TRUE;
> > -      *Ptr          = READ_ARRAY_CMD;
> > +      *Ptr       = WRITE_BYTE_CMD;
> > +      *Ptr       = OriginalUint8;
> > +      *Ptr       = READ_STATUS_CMD;
> > +      ProbeUint8 = *Ptr;
> > +      *Ptr       = READ_ARRAY_CMD;
> > +      if (ProbeUint8 & 0x10 /* programming error */) {
> > +        DEBUG ((DEBUG_INFO, "QemuFlashDetected => FD behaves as FLASH, write-protected\n"));
> > +      } else {
> > +        DEBUG ((DEBUG_INFO, "QemuFlashDetected => FD behaves as FLASH, writable\n"));
> > +        FlashDetected = TRUE;
> > +      }
> >      }
> >    }
> >
> > --
> > 2.40.1
> >
>
> - Oliver
>