diff options
| -rw-r--r-- | OvmfPkg/Include/Library/QemuFwCfgLib.h | 16 | ||||
| -rw-r--r-- | OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLib.c | 44 |
2 files changed, 60 insertions, 0 deletions
diff --git a/OvmfPkg/Include/Library/QemuFwCfgLib.h b/OvmfPkg/Include/Library/QemuFwCfgLib.h index 3e017d53a9..41c3817470 100644 --- a/OvmfPkg/Include/Library/QemuFwCfgLib.h +++ b/OvmfPkg/Include/Library/QemuFwCfgLib.h @@ -159,6 +159,22 @@ QemuFwCfgWriteBytes ( /**
+ Skip bytes in the firmware configuration item.
+
+ Increase the offset of the firmware configuration item without transferring
+ bytes between the item and a caller-provided buffer. Subsequent read, write
+ or skip operations will commence at the increased offset.
+
+ @param[in] Size Number of bytes to skip.
+**/
+VOID
+EFIAPI
+QemuFwCfgSkipBytes (
+ IN UINTN Size
+ );
+
+
+/**
Reads a UINT8 firmware configuration value
@return Value of Firmware Configuration item read
diff --git a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLib.c b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLib.c index 6b6b2c7726..7744873217 100644 --- a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLib.c +++ b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLib.c @@ -193,6 +193,50 @@ QemuFwCfgWriteBytes ( /**
+ Skip bytes in the firmware configuration item.
+
+ Increase the offset of the firmware configuration item without transferring
+ bytes between the item and a caller-provided buffer. Subsequent read, write
+ or skip operations will commence at the increased offset.
+
+ @param[in] Size Number of bytes to skip.
+**/
+VOID
+EFIAPI
+QemuFwCfgSkipBytes (
+ IN UINTN Size
+ )
+{
+ UINTN ChunkSize;
+ UINT8 SkipBuffer[256];
+
+ if (!InternalQemuFwCfgIsAvailable ()) {
+ return;
+ }
+
+ if (InternalQemuFwCfgDmaIsAvailable () && Size <= MAX_UINT32) {
+ InternalQemuFwCfgDmaBytes ((UINT32)Size, NULL, FW_CFG_DMA_CTL_SKIP);
+ return;
+ }
+
+ //
+ // Emulate the skip by reading data in chunks, and throwing it away. The
+ // implementation below is suitable even for phases where RAM or dynamic
+ // allocation is not available or appropriate. It also doesn't affect the
+ // static data footprint for client modules. Large skips are not expected,
+ // therefore this fallback is not performance critical. The size of
+ // SkipBuffer is thought not to exert a large pressure on the stack in any
+ // phase.
+ //
+ while (Size > 0) {
+ ChunkSize = MIN (Size, sizeof SkipBuffer);
+ IoReadFifo8 (0x511, ChunkSize, SkipBuffer);
+ Size -= ChunkSize;
+ }
+}
+
+
+/**
Reads a UINT8 firmware configuration value
@return Value of Firmware Configuration item read
|