[edk2-devel] [PATCH v2 1/1] OvmfPkg/QemuFlashFvbServicesRuntimeDxe: refine flash detection
Oliver Steffen
osteffen at redhat.com
Thu Jun 1 08:22:31 UTC 2023
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 >,<
> 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 at 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
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