[edk2-devel] [PATCH 06/11] OvmfPkg/VirtNorFlashDxe: avoid array mode switch after each word write

[Ard Biesheuvel]

NorFlashWriteSingleWord() switches into programming mode and back into
array mode for every single word that it writes. Under KVM, this
involves tearing down the read-only memslot, and setting it up again,
which is costly and unnecessary.

Instead, move the array mode switch into the callers, and only make the
switch when the writing is done.

Signed-off-by: Ard Biesheuvel <a...@kernel.org>
---
 OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c    | 12 +++---------
 OvmfPkg/VirtNorFlashDxe/VirtNorFlashDxe.c |  3 +++
 2 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c 
b/OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c
index f41d9d372f49..0a5c5d48c738 100644
--- a/OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c
+++ b/OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c
@@ -205,9 +205,6 @@ NorFlashWriteSingleWord (
     SEND_NOR_COMMAND (Instance->DeviceBaseAddress, 0, 
P30_CMD_CLEAR_STATUS_REGISTER);
   }
 
-  // Put device back into Read Array mode
-  SEND_NOR_COMMAND (Instance->DeviceBaseAddress, 0, P30_CMD_READ_ARRAY);
-
   return Status;
 }
 
@@ -286,8 +283,7 @@ NorFlashWriteBuffer (
 
   // The buffer was not available for writing
   if (WaitForBuffer == 0) {
-    Status = EFI_DEVICE_ERROR;
-    goto EXIT;
+    return EFI_DEVICE_ERROR;
   }
 
   // From now on we work in 32-bit words
@@ -337,10 +333,6 @@ NorFlashWriteBuffer (
     SEND_NOR_COMMAND (Instance->DeviceBaseAddress, 0, 
P30_CMD_CLEAR_STATUS_REGISTER);
   }
 
-EXIT:
-  // Put device back into Read Array mode
-  SEND_NOR_COMMAND (Instance->DeviceBaseAddress, 0, P30_CMD_READ_ARRAY);
-
   return Status;
 }
 
@@ -739,6 +731,8 @@ NorFlashWriteSingleBlock (
       }
 
       TempStatus = NorFlashWriteSingleWord (Instance, WordAddr, WordToWrite);
+      // Put device back into Read Array mode
+      SEND_NOR_COMMAND (Instance->DeviceBaseAddress, 0, P30_CMD_READ_ARRAY);
       if (EFI_ERROR (TempStatus)) {
         return EFI_DEVICE_ERROR;
       }
diff --git a/OvmfPkg/VirtNorFlashDxe/VirtNorFlashDxe.c 
b/OvmfPkg/VirtNorFlashDxe/VirtNorFlashDxe.c
index 2ceda226359c..f9a41f6aab0f 100644
--- a/OvmfPkg/VirtNorFlashDxe/VirtNorFlashDxe.c
+++ b/OvmfPkg/VirtNorFlashDxe/VirtNorFlashDxe.c
@@ -280,6 +280,9 @@ NorFlashWriteFullBlock (
   }
 
 EXIT:
+  // Put device back into Read Array mode
+  SEND_NOR_COMMAND (Instance->DeviceBaseAddress, 0, P30_CMD_READ_ARRAY);
+
   if (!EfiAtRuntime ()) {
     // Interruptions can resume.
     gBS->RestoreTPL (OriginalTPL);
-- 
2.35.1



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