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OvmfPkg/VirtNorFlashDxe: clarify block write logic & fix shadowbuffer reads 

Introduce 'Start' and 'End' variables to make it easier to follow the
logic and code flow.  Also add a ascii art diagram (based on a
suggestion by Laszlo).

This also fixes the 'Size' calculation for the NorFlashRead() call.
Without this patch the code will read only one instead of two
P30_MAX_BUFFER_SIZE_IN_BYTES blocks in case '*NumBytes' is smaller than
P30_MAX_BUFFER_SIZE_IN_BYTES but 'Offset + *NumBytes' is not, i.e. the
update range crosses a P30_MAX_BUFFER_SIZE_IN_BYTES boundary.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20240116171105.37831-3-kraxel@redhat.com>
This commit is contained in:
Gerd Hoffmann 2024-01-16 18:11:01 +01:00 committed by mergify[bot]
parent 0395045ae3
commit 35d8ea8097
1 changed files with 28 additions and 8 deletions
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36
OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c
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@ -520,6 +520,7 @@ NorFlashWriteSingleBlock (
UINTN BlockSize; UINTN BlockSize;
UINTN BlockAddress; UINTN BlockAddress;
UINT8 *OrigData; UINT8 *OrigData;
UINTN Start, End;
DEBUG ((DEBUG_BLKIO, "NorFlashWriteSingleBlock(Parameters: Lba=%ld, Offset=0x%x, *NumBytes=0x%x, Buffer @ 0x%08x)\n", Lba, Offset, *NumBytes, Buffer)); DEBUG ((DEBUG_BLKIO, "NorFlashWriteSingleBlock(Parameters: Lba=%ld, Offset=0x%x, *NumBytes=0x%x, Buffer @ 0x%08x)\n", Lba, Offset, *NumBytes, Buffer));
@ -555,7 +556,28 @@ NorFlashWriteSingleBlock (
// To avoid pathological cases were a 2 byte write is disregarded because it // 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 // occurs right at a 128 byte buffered write alignment boundary, permit up to
// twice the max buffer size, and perform two writes if needed. // twice the max buffer size, and perform two writes if needed.
if ((*NumBytes + (Offset & BOUNDARY_OF_32_WORDS)) <= (2 * P30_MAX_BUFFER_SIZE_IN_BYTES)) { //
// 0 128 256
// [----------------|----------------]
// ^ ^ ^ ^
// | | | |
// | | | End, the next "word" boundary beyond
// | | | the (logical) update
// | | |
// | | (Offset & BOUNDARY_OF_32_WORDS) + NumBytes;
// | | i.e., the relative offset inside (or just past)
// | | the *double-word* such that it is the
// | | *exclusive* end of the (logical) update.
// | |
// | Offset & BOUNDARY_OF_32_WORDS; i.e., Offset within the "word";
// | this is where the (logical) update is supposed to start
// |
// Start = Offset & ~BOUNDARY_OF_32_WORDS; i.e., Offset truncated to "word" boundary
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)) {
// Check to see if we need to erase before programming the data into NOR. // 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. // 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. // After a block is erased all bits in the block is set to 1.
@ -565,8 +587,8 @@ NorFlashWriteSingleBlock (
Status = NorFlashRead ( Status = NorFlashRead (
Instance, Instance,
Lba, Lba,
Offset & ~BOUNDARY_OF_32_WORDS, Start,
(*NumBytes | BOUNDARY_OF_32_WORDS) + 1, End - Start,
Instance->ShadowBuffer Instance->ShadowBuffer
); );
if (EFI_ERROR (Status)) { if (EFI_ERROR (Status)) {
@ -601,7 +623,7 @@ NorFlashWriteSingleBlock (
Status = NorFlashWriteBuffer ( Status = NorFlashWriteBuffer (
Instance, Instance,
BlockAddress + (Offset & ~BOUNDARY_OF_32_WORDS), BlockAddress + Start,
P30_MAX_BUFFER_SIZE_IN_BYTES, P30_MAX_BUFFER_SIZE_IN_BYTES,
Instance->ShadowBuffer Instance->ShadowBuffer
); );
@ -609,12 +631,10 @@ NorFlashWriteSingleBlock (
goto Exit; goto Exit;
} }
if ((*NumBytes + (Offset & BOUNDARY_OF_32_WORDS)) > P30_MAX_BUFFER_SIZE_IN_BYTES) { if ((End - Start) > P30_MAX_BUFFER_SIZE_IN_BYTES) {
BlockAddress += P30_MAX_BUFFER_SIZE_IN_BYTES;
Status = NorFlashWriteBuffer ( Status = NorFlashWriteBuffer (
Instance, Instance,
BlockAddress + (Offset & ~BOUNDARY_OF_32_WORDS), BlockAddress + Start + P30_MAX_BUFFER_SIZE_IN_BYTES,
P30_MAX_BUFFER_SIZE_IN_BYTES, P30_MAX_BUFFER_SIZE_IN_BYTES,
Instance->ShadowBuffer + P30_MAX_BUFFER_SIZE_IN_BYTES Instance->ShadowBuffer + P30_MAX_BUFFER_SIZE_IN_BYTES
); );