OvmfPkg/QemuFwCfgLib: support QEMU's DMA-like fw_cfg access method
The benefits of the DMA-like access method are (a) speed, (b) write
support in QEMU 2.9+.
(IOPort-based write support was discontinued in QEMU 2.4, and the
DMA-based one is being added to QEMU 2.9. Write support needs no separate
feature detection because writeability is governed on the level of
individual fw_cfg files -- if a file meant to be written by the firmware
exists in the directory, then it is writeable with the DMA method.)
We don't enable this feature for the SEC library instance, because:
- the SEC instance remains without clients (I've checked that it builds
though),
- in SEC, any possible fw_cfg use is expected to be small and read-only.
Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
diff --git a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLib.c b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLib.c
index 804d5b0..0bbf121 100644
--- a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLib.c
+++ b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLib.c
@@ -99,6 +99,70 @@
/**
+ Transfer an array of bytes using the DMA interface.
+
+ @param[in] Size Size in bytes to transfer.
+ @param[in,out] Buffer Buffer to read data into or write data from. May be
+ NULL if Size is zero.
+ @param[in] Write TRUE if writing to fw_cfg from Buffer, FALSE if
+ reading from fw_cfg into Buffer.
+**/
+VOID
+InternalQemuFwCfgDmaBytes (
+ IN UINT32 Size,
+ IN OUT VOID *Buffer OPTIONAL,
+ IN BOOLEAN Write
+ )
+{
+ volatile FW_CFG_DMA_ACCESS Access;
+ UINT32 AccessHigh, AccessLow;
+ UINT32 Status;
+
+ if (Size == 0) {
+ return;
+ }
+
+ Access.Control = SwapBytes32 (
+ Write ? FW_CFG_DMA_CTL_WRITE : FW_CFG_DMA_CTL_READ
+ );
+ Access.Length = SwapBytes32 (Size);
+ Access.Address = SwapBytes64 ((UINTN)Buffer);
+
+ //
+ // Delimit the transfer from (a) modifications to Access, (b) in case of a
+ // write, from writes to Buffer by the caller.
+ //
+ MemoryFence ();
+
+ //
+ // Start the transfer.
+ //
+ AccessHigh = (UINT32)RShiftU64 ((UINTN)&Access, 32);
+ AccessLow = (UINT32)(UINTN)&Access;
+ IoWrite32 (0x514, SwapBytes32 (AccessHigh));
+ IoWrite32 (0x518, SwapBytes32 (AccessLow));
+
+ //
+ // Don't look at Access.Control before starting the transfer.
+ //
+ MemoryFence ();
+
+ //
+ // Wait for the transfer to complete.
+ //
+ do {
+ Status = SwapBytes32 (Access.Control);
+ ASSERT ((Status & FW_CFG_DMA_CTL_ERROR) == 0);
+ } while (Status != 0);
+
+ //
+ // After a read, the caller will want to use Buffer.
+ //
+ MemoryFence ();
+}
+
+
+/**
Reads firmware configuration bytes into a buffer
@param[in] Size - Size in bytes to read
@@ -112,6 +176,10 @@
IN VOID *Buffer OPTIONAL
)
{
+ if (InternalQemuFwCfgDmaIsAvailable () && Size <= MAX_UINT32) {
+ InternalQemuFwCfgDmaBytes ((UINT32)Size, Buffer, FALSE);
+ return;
+ }
IoReadFifo8 (0x511, Size, Buffer);
}
@@ -160,6 +228,10 @@
)
{
if (InternalQemuFwCfgIsAvailable ()) {
+ if (InternalQemuFwCfgDmaIsAvailable () && Size <= MAX_UINT32) {
+ InternalQemuFwCfgDmaBytes ((UINT32)Size, Buffer, TRUE);
+ return;
+ }
IoWriteFifo8 (0x511, Size, Buffer);
}
}
diff --git a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLibInternal.h b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLibInternal.h
index 5b162bf..6e87c62 100644
--- a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLibInternal.h
+++ b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLibInternal.h
@@ -30,4 +30,17 @@
VOID
);
+
+/**
+ Returns a boolean indicating whether QEMU provides the DMA-like access method
+ for fw_cfg.
+
+ @retval TRUE The DMA-like access method is available.
+ @retval FALSE The DMA-like access method is unavailable.
+**/
+BOOLEAN
+InternalQemuFwCfgDmaIsAvailable (
+ VOID
+ );
+
#endif
diff --git a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgPeiDxe.c b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgPeiDxe.c
index 88d88c0..ac05f4c 100644
--- a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgPeiDxe.c
+++ b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgPeiDxe.c
@@ -20,6 +20,7 @@
#include "QemuFwCfgLibInternal.h"
STATIC BOOLEAN mQemuFwCfgSupported = FALSE;
+STATIC BOOLEAN mQemuFwCfgDmaSupported;
/**
@@ -53,8 +54,10 @@
//
// Enable the access routines while probing to see if it is supported.
+ // For probing we always use the IO Port (IoReadFifo8()) access method.
//
mQemuFwCfgSupported = TRUE;
+ mQemuFwCfgDmaSupported = FALSE;
QemuFwCfgSelectItem (QemuFwCfgItemSignature);
Signature = QemuFwCfgRead32 ();
@@ -70,7 +73,12 @@
return RETURN_SUCCESS;
}
- DEBUG ((EFI_D_INFO, "QemuFwCfg interface is supported.\n"));
+ if ((Revision & FW_CFG_F_DMA) == 0) {
+ DEBUG ((DEBUG_INFO, "QemuFwCfg interface (IO Port) is supported.\n"));
+ } else {
+ mQemuFwCfgDmaSupported = TRUE;
+ DEBUG ((DEBUG_INFO, "QemuFwCfg interface (DMA) is supported.\n"));
+ }
return RETURN_SUCCESS;
}
@@ -91,3 +99,18 @@
{
return mQemuFwCfgSupported;
}
+
+/**
+ Returns a boolean indicating whether QEMU provides the DMA-like access method
+ for fw_cfg.
+
+ @retval TRUE The DMA-like access method is available.
+ @retval FALSE The DMA-like access method is unavailable.
+**/
+BOOLEAN
+InternalQemuFwCfgDmaIsAvailable (
+ VOID
+ )
+{
+ return mQemuFwCfgDmaSupported;
+}
diff --git a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgSec.c b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgSec.c
index 56c59ca..465ccbe 100644
--- a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgSec.c
+++ b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgSec.c
@@ -79,3 +79,18 @@
//
return TRUE;
}
+
+/**
+ Returns a boolean indicating whether QEMU provides the DMA-like access method
+ for fw_cfg.
+
+ @retval TRUE The DMA-like access method is available.
+ @retval FALSE The DMA-like access method is unavailable.
+**/
+BOOLEAN
+InternalQemuFwCfgDmaIsAvailable (
+ VOID
+ )
+{
+ return FALSE;
+}
