On 1/15/24 16:59, Gerd Hoffmann wrote:
> Raise the limit for writes without block erase from two to four
> P30_MAX_BUFFER_SIZE_IN_BYTES blocks. With this in place almost all efi
> variable updates are handled without block erase. With the old limit
> some variable updates (with device paths) took the block erase code
> path.
>
> Signed-off-by: Gerd Hoffmann <kra...@redhat.com>
> ---
> OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c | 18 ++++++++++--------
> 1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c
> b/OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c
> index 67610d6920f7..d80e9f0a2f3a 100644
> --- a/OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c
> +++ b/OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c
> @@ -550,13 +550,15 @@ NorFlashWriteSingleBlock (
> return EFI_BAD_BUFFER_SIZE;
> }
>
> - // Pick P30_MAX_BUFFER_SIZE_IN_BYTES (== 128 bytes) as a good start for
> word
> - // operations as opposed to erasing the block and writing the data
> regardless
> - // if an erase is really needed. It looks like most individual NV variable
> - // writes are smaller than 128 bytes.
> - // To avoid pathological cases were a 2 byte write is disregarded because
> it
> - // occurs right at a 128 byte buffered write alignment boundary, permit up
> to
> - // twice the max buffer size, and perform two writes if needed.
> + // Pick 4 * P30_MAX_BUFFER_SIZE_IN_BYTES (== 512 bytes) as a good
> + // start for word operations as opposed to erasing the block and
> + // writing the data regardless if an erase is really needed.
> + //
> + // Many NV variable updates are small enough for a a single
> + // P30_MAX_BUFFER_SIZE_IN_BYTES block write. In case the update is
> + // larger than a single block, or the update crosses a
> + // P30_MAX_BUFFER_SIZE_IN_BYTES boundary (as shown in the diagram
> + // below), or both, we might have to write two or more blocks.
> //
> // 0 128 256
> // [----------------|----------------]
> @@ -577,7 +579,7 @@ NorFlashWriteSingleBlock (
> Start = Offset & ~BOUNDARY_OF_32_WORDS;
> End = ALIGN_VALUE (Offset + *NumBytes, P30_MAX_BUFFER_SIZE_IN_BYTES);
>
> - if ((End - Start) <= (2 * P30_MAX_BUFFER_SIZE_IN_BYTES)) {
> + if ((End - Start) <= (4 * P30_MAX_BUFFER_SIZE_IN_BYTES)) {
> // Check to see if we need to erase before programming the data into NOR.
> // If the destination bits are only changing from 1s to 0s we can just
> write.
> // After a block is erased all bits in the block is set to 1.
Reviewed-by: Laszlo Ersek <ler...@redhat.com>
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