[edk2-staging/RiscV64QemuVirt PATCH V4 30/34] OvmfPkg/NorFlashDxe: Avoid switching to array mode during writes

["Sunil V L" <sunilvl@ventanamicro.com>]

Switching to array mode (i.e., ROM memory mode rather than NOR flash
programming mode) is rather costly when running under KVM emulation, as it
involves setting up the read-only memslot in the hypervisor's stage 2
page tables. So let's avoid jumping between modes unnecessarily, and
only switch back to array mode when we are done writing to flash.

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Leif Lindholm <quic_llindhol@quicinc.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 OvmfPkg/Drivers/NorFlashDxe/NorFlash.c             | 9 +++------
 OvmfPkg/Drivers/NorFlashDxe/NorFlashDxe.c          | 3 +++
 OvmfPkg/Drivers/NorFlashDxe/NorFlashStandaloneMm.c | 3 +++
 3 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/OvmfPkg/Drivers/NorFlashDxe/NorFlash.c b/OvmfPkg/Drivers/NorFlashDxe/NorFlash.c
index c2a6aa281578..cdc6b5da8bfb 100644
--- a/OvmfPkg/Drivers/NorFlashDxe/NorFlash.c
+++ b/OvmfPkg/Drivers/NorFlashDxe/NorFlash.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;
 }
 
@@ -338,9 +335,6 @@ NorFlashWriteBuffer (
   }
 
 EXIT:
-  // Put device back into Read Array mode
-  SEND_NOR_COMMAND (Instance->DeviceBaseAddress, 0, P30_CMD_READ_ARRAY);
-
   return Status;
 }
 
@@ -750,6 +744,9 @@ 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/Drivers/NorFlashDxe/NorFlashDxe.c b/OvmfPkg/Drivers/NorFlashDxe/NorFlashDxe.c
index f7b92de21a57..862a8e621fd0 100644
--- a/OvmfPkg/Drivers/NorFlashDxe/NorFlashDxe.c
+++ b/OvmfPkg/Drivers/NorFlashDxe/NorFlashDxe.c
@@ -316,6 +316,9 @@ 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);
diff --git a/OvmfPkg/Drivers/NorFlashDxe/NorFlashStandaloneMm.c b/OvmfPkg/Drivers/NorFlashDxe/NorFlashStandaloneMm.c
index b72ad97b0b55..f6dec84176d4 100644
--- a/OvmfPkg/Drivers/NorFlashDxe/NorFlashStandaloneMm.c
+++ b/OvmfPkg/Drivers/NorFlashDxe/NorFlashStandaloneMm.c
@@ -270,6 +270,9 @@ NorFlashWriteFullBlock (
   }
 
 EXIT:
+  // Put device back into Read Array mode
+  SEND_NOR_COMMAND (Instance->DeviceBaseAddress, 0, P30_CMD_READ_ARRAY);
+
   if (EFI_ERROR (Status)) {
     DEBUG ((DEBUG_ERROR, "NOR FLASH Programming [WriteSingleBlock] failed at address 0x%08x. Exit Status = \"%r\".\n", WordAddress, Status));
   }
-- 
2.38.0