ArmVirtPkg: introduce compile and runtime control of serial debug log level

Add a new PCD `PcdSerialDebugPrintErrorLevel` that overrides the verbosity
set in `DebugPrintErrorLevel` for the serial port debug output and does
not affect memory debug logging.

Accepted values are:
- "silent": DEBUG_ERROR only
- "verbose": use the `DebugPrintErrorLevel` value.
- a hex bitmask (e.g. "0x80000040").

This PCD value can be overridden at runtime using the fw_cfg entry
"opt/org.tianocore/DebugLevel" without rebuilding the firmware.

The runtime override takes priority over the compile-time one. When
neither is set, the serial output uses the compiled-in
PcdDebugPrintErrorLevel.

SEC and PEI_CORE phases do not support this override because they run
from flash, where global variables are not available. Supporting it
would require parsing the device tree on every debug write to locate
the fw_cfg device and read the DebugLevel value — unnecessary overhead
given the low volume of logs in those phases.

ParseSerialDebugLevel() is duplicated as a STATIC function in Flash.c
and PlatformPeiLib.c rather than shared via a header, because EDK2
coding style forbids function definitions in headers. A dedicated
library class would be excessive for a small helper with only two
consumers.

Example QEMU command line:

  -fw_cfg name=opt/org.tianocore/DebugLevel,string=silent
  -fw_cfg name=opt/org.tianocore/DebugLevel,string=verbose
  -fw_cfg name=opt/org.tianocore/DebugLevel,string=0x80000000

Suggested-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Luigi Leonardi <leonardi@redhat.com>

ArmVirtPkg/ArmVirtCloudHv.dsc

@@ -46,6 +46,8 @@
 
   TpmPlatformHierarchyLib|SecurityPkg/Library/PeiDxeTpmPlatformHierarchyLibNull/PeiDxeTpmPlatformHierarchyLib.inf
   ArmTransferListLib|ArmPkg/Library/ArmTransferListLib/ArmTransferListLib.inf
+  QemuFwCfgLib|OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLibNull.inf
+  QemuFwCfgSimpleParserLib|OvmfPkg/Library/QemuFwCfgSimpleParserLib/QemuFwCfgSimpleParserLib.inf
 
 !include MdePkg/MdeLibs.dsc.inc
 

ArmVirtPkg/ArmVirtPkg.dec

@@ -51,3 +51,8 @@
   # Cloud Hypervisor has no other way to pass Rsdp address to the guest except use a PCD.
   #
   gArmVirtTokenSpaceGuid.PcdCloudHvAcpiRsdpBaseAddress|0x0|UINT64|0x00000005
+
+  ## Serial debug log level override.  Accepts "silent", "verbose", or a
+  #  hex bitmask (e.g. "0x80000040").  "verbose" falls back to the
+  #  compiled-in PcdDebugPrintErrorLevel.
+  gArmVirtTokenSpaceGuid.PcdSerialDebugPrintErrorLevel|"verbose"|VOID*|0x00000006

ArmVirtPkg/ArmVirtQemuKernel.dsc

@@ -75,6 +75,9 @@
 
   ArmMonitorLib|ArmVirtPkg/Library/ArmVirtMonitorLib/ArmVirtMonitorLib.inf
 
+[LibraryClasses.common.SEC]
+  QemuFwCfgLib|OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLibNull.inf
+
 [LibraryClasses.common.DXE_DRIVER]
   AcpiPlatformLib|OvmfPkg/Library/AcpiPlatformLib/DxeAcpiPlatformLib.inf
   ReportStatusCodeLib|MdeModulePkg/Library/DxeReportStatusCodeLib/DxeReportStatusCodeLib.inf

ArmVirtPkg/Include/Guid/EarlyPL011BaseAddress.h

@@ -21,9 +21,16 @@ typedef struct {
   //
   // for SerialPortLib and console IO
   //
-  UINT64    ConsoleAddress;
+  UINT64     ConsoleAddress;
   //
   // for DebugLib; may equal ConsoleAddress if there's only one PL011 UART
   //
-  UINT64    DebugAddress;
+  UINT64     DebugAddress;
+  //
+  // Serial debug log level override from fw_cfg "opt/org.tianocore/DebugLevel"
+  // or PcdSerialDebugPrintErrorLevel.  DebugLevelSet is TRUE when an override
+  // is active; DebugLevel contains the parsed bitmask.
+  //
+  BOOLEAN    DebugLevelSet;
+  UINT32     DebugLevel;
 } EARLY_PL011_BASE_ADDRESS;

ArmVirtPkg/Library/DebugLibFdtPL011Uart/DebugLib.c

@@ -94,17 +94,28 @@ DebugPrintMarker (
   IN  BASE_LIST    BaseListMarker
   )
 {
-  CHAR8  Buffer[MAX_DEBUG_MESSAGE_LENGTH];
+  CHAR8       Buffer[MAX_DEBUG_MESSAGE_LENGTH];
+  UINT32      SerialDebugLevel;
+  UINT32      DebugLevel;
+  EFI_STATUS  Status;
 
   //
   // If Format is NULL, then ASSERT().
   //
   ASSERT (Format != NULL);
 
+  DebugLevel = GetDebugPrintErrorLevel ();
+
+  Status = GetSerialDebugPrintErrorLevel (&SerialDebugLevel);
+  if (EFI_ERROR (Status)) {
+    SerialDebugLevel = DebugLevel;
+  }
+
   //
-  // Check driver debug mask value and global mask
+  // SerialDebugLevel can be more verbose than DebugLevel.
+  // Check if we have something to print
   //
-  if ((ErrorLevel & GetDebugPrintErrorLevel ()) == 0) {
+  if (((ErrorLevel & DebugLevel) == 0) && ((ErrorLevel & SerialDebugLevel) == 0)) {
     return;
   }
 
@@ -118,12 +129,19 @@ DebugPrintMarker (
   }
 
   //
-  // Send string to Memory Debug Log if enabled
+  // Send string to Memory Debug Log if enabled and error level matches
   //
-  if (MemDebugLogEnabled ()) {
+  if (((ErrorLevel & DebugLevel) != 0) && MemDebugLogEnabled ()) {
     MemDebugLogWrite ((CHAR8 *)Buffer, AsciiStrLen (Buffer));
   }
 
+  //
+  // Check runtime debug mask value and global mask
+  //
+  if ((ErrorLevel & SerialDebugLevel) == 0) {
+    return;
+  }
+
   //
   // Send the print string to a Serial Port
   //

ArmVirtPkg/Library/DebugLibFdtPL011Uart/DebugLibFdtPL011UartFlash.inf

@@ -50,6 +50,7 @@
 
 [FixedPcd]
   gArmPlatformTokenSpaceGuid.PL011UartClkInHz
+  gArmVirtTokenSpaceGuid.PcdSerialDebugPrintErrorLevel
   gEfiMdePkgTokenSpaceGuid.PcdUartDefaultBaudRate
   gEfiMdePkgTokenSpaceGuid.PcdUartDefaultDataBits
   gEfiMdePkgTokenSpaceGuid.PcdUartDefaultParity

ArmVirtPkg/Library/DebugLibFdtPL011Uart/Flash.c

@@ -6,12 +6,64 @@
   SPDX-License-Identifier: BSD-2-Clause-Patent
 **/
 
+#include <Library/BaseLib.h>
+#include <Library/DebugLib.h>
 #include <Library/FdtSerialPortAddressLib.h>
 #include <Library/PL011UartLib.h>
 #include <Library/PcdLib.h>
 
 #include "Write.h"
 
+//
+// Duplicated in ArmVirtPkg/Library/PlatformPeiLib/PlatformPeiLib.c —
+// keep both copies in sync.
+//
+
+/**
+  Parse a serial debug level string.
+
+  Accepted values are "silent" (DEBUG_ERROR only), "verbose" (no
+  override), or a hex bitmask (e.g. "0x80000040").
+
+  @param[in]  String      NUL-terminated ASCII string to parse.
+  @param[out] DebugLevel  On success, the parsed debug level bitmask.
+
+  @retval TRUE   String was recognised; *DebugLevel is valid.
+  @retval FALSE  String is NULL, "verbose", or unrecognised; no override.
+**/
+STATIC
+BOOLEAN
+ParseSerialDebugLevel (
+  IN  CONST CHAR8  *String,
+  OUT UINT32       *DebugLevel
+  )
+{
+  UINT64  Value;
+  CHAR8   *End;
+
+  if ((String == NULL) || (DebugLevel == NULL)) {
+    return FALSE;
+  }
+
+  if (AsciiStrCmp (String, "silent") == 0) {
+    *DebugLevel = DEBUG_ERROR;
+    return TRUE;
+  }
+
+  if (AsciiStrCmp (String, "verbose") == 0) {
+    return FALSE;
+  }
+
+  if (!EFI_ERROR (AsciiStrHexToUint64S (String, &End, &Value)) &&
+      (*End == '\0'))
+  {
+    *DebugLevel = (UINT32)Value;
+    return TRUE;
+  }
+
+  return FALSE;
+}
+
 /**
   (Copied from SerialPortWrite() in "MdePkg/Include/Library/SerialPortLib.h" at
   commit c4547aefb3d0, with the Buffer non-nullity assertion removed:)
@@ -105,3 +157,35 @@ DebugLibFdtPL011UartWrite (
 
   return PL011UartWrite ((UINTN)DebugAddress, Buffer, NumberOfBytes);
 }
+
+/**
+  Retrieve the serial debug print error level override.
+
+  The flash variant parses the compile-time PCD only.  The fw_cfg
+  override is not available in SEC/PEI_CORE phases.
+
+  @param[out] Value  On success, the debug log level bitmask.
+
+  @retval EFI_SUCCESS    The debug level was retrieved successfully.
+  @retval EFI_INVALID_PARAMETER  Value is NULL.
+  @retval EFI_NOT_FOUND  No override is configured (e.g. "verbose").
+**/
+EFI_STATUS
+GetSerialDebugPrintErrorLevel (
+  OUT UINT32  *Value
+  )
+{
+  CONST CHAR8  *String;
+
+  if (Value == NULL) {
+    return EFI_INVALID_PARAMETER;
+  }
+
+  String = (CONST CHAR8 *)PcdGetPtr (PcdSerialDebugPrintErrorLevel);
+
+  if (ParseSerialDebugLevel (String, Value)) {
+    return EFI_SUCCESS;
+  }
+
+  return EFI_NOT_FOUND;
+}

ArmVirtPkg/Library/DebugLibFdtPL011Uart/Ram.c

@@ -20,6 +20,8 @@
 
 UINTN          mDebugLibFdtPL011UartAddress;
 RETURN_STATUS  mDebugLibFdtPL011UartPermanentStatus = RETURN_SUCCESS;
+BOOLEAN        mSerialDebugLevelSet;
+UINT32         mSerialDebugLevel;
 
 /**
   Statefully initialize both the library instance and the debug PL011 UART.
@@ -62,6 +64,11 @@ Initialize (
     goto Failed;
   }
 
+  if (UartBase->DebugLevelSet) {
+    mSerialDebugLevelSet = TRUE;
+    mSerialDebugLevel    = UartBase->DebugLevel;
+  }
+
   BaudRate         = (UINTN)PcdGet64 (PcdUartDefaultBaudRate);
   ReceiveFifoDepth = 0; // Use the default value for Fifo depth
   Parity           = (EFI_PARITY_TYPE)PcdGet8 (PcdUartDefaultParity);
@@ -122,3 +129,36 @@ DebugLibFdtPL011UartWrite (
 
   return PL011UartWrite (mDebugLibFdtPL011UartAddress, Buffer, NumberOfBytes);
 }
+
+/**
+  Retrieve the serial debug print error level override.
+
+  @param[out] Value  On success, the debug log level bitmask.
+
+  @retval EFI_SUCCESS            The debug level was retrieved successfully.
+  @retval EFI_INVALID_PARAMETER  Value is NULL.
+  @retval EFI_NOT_FOUND          The debug level is not available.
+**/
+EFI_STATUS
+GetSerialDebugPrintErrorLevel (
+  OUT UINT32  *Value
+  )
+{
+  RETURN_STATUS  Status;
+
+  if (Value == NULL) {
+    return EFI_INVALID_PARAMETER;
+  }
+
+  Status = Initialize ();
+  if (RETURN_ERROR (Status)) {
+    return EFI_NOT_FOUND;
+  }
+
+  if (mSerialDebugLevelSet) {
+    *Value = mSerialDebugLevel;
+    return EFI_SUCCESS;
+  }
+
+  return EFI_NOT_FOUND;
+}

ArmVirtPkg/Library/DebugLibFdtPL011Uart/Write.h

@@ -34,3 +34,17 @@ DebugLibFdtPL011UartWrite (
   IN UINT8  *Buffer,
   IN UINTN  NumberOfBytes
   );
+
+/**
+  Retrieve the serial debug print error level override.
+
+  @param[out] Value  On success, the debug log level bitmask.
+
+  @retval EFI_SUCCESS            The debug level was retrieved successfully.
+  @retval EFI_INVALID_PARAMETER  Value is NULL.
+  @retval EFI_NOT_FOUND          The debug level is not available.
+**/
+EFI_STATUS
+GetSerialDebugPrintErrorLevel (
+  OUT UINT32  *Value
+  );

ArmVirtPkg/Library/PlatformPeiLib/PlatformPeiLib.c

@@ -9,6 +9,7 @@
 
 #include <PiPei.h>
 
+#include <Library/BaseLib.h>
 #include <Library/BaseMemoryLib.h>
 #include <Library/MemoryAllocationLib.h>
 #include <Library/DebugLib.h>
@@ -17,10 +18,61 @@
 #include <Library/PcdLib.h>
 #include <Library/PeiServicesLib.h>
 #include <Library/FdtSerialPortAddressLib.h>
+#include <Library/QemuFwCfgSimpleParserLib.h>
 
 #include <Guid/EarlyPL011BaseAddress.h>
 #include <Guid/FdtHob.h>
 
+//
+// Duplicated in ArmVirtPkg/Library/DebugLibFdtPL011Uart/Flash.c —
+// keep both copies in sync.
+//
+
+/**
+  Parse a serial debug level string.
+
+  Accepted values are "silent" (DEBUG_ERROR only), "verbose" (no
+  override), or a hex bitmask (e.g. "0x80000040").
+
+  @param[in]  String      NUL-terminated ASCII string to parse.
+  @param[out] DebugLevel  On success, the parsed debug level bitmask.
+
+  @retval TRUE   String was recognised; *DebugLevel is valid.
+  @retval FALSE  String is NULL, "verbose", or unrecognised; no override.
+**/
+STATIC
+BOOLEAN
+ParseSerialDebugLevel (
+  IN  CONST CHAR8  *String,
+  OUT UINT32       *DebugLevel
+  )
+{
+  UINT64  Value;
+  CHAR8   *End;
+
+  if ((String == NULL) || (DebugLevel == NULL)) {
+    return FALSE;
+  }
+
+  if (AsciiStrCmp (String, "silent") == 0) {
+    *DebugLevel = DEBUG_ERROR;
+    return TRUE;
+  }
+
+  if (AsciiStrCmp (String, "verbose") == 0) {
+    return FALSE;
+  }
+
+  if (!EFI_ERROR (AsciiStrHexToUint64S (String, &End, &Value)) &&
+      (*End == '\0'))
+  {
+    *DebugLevel = (UINT32)Value;
+    return TRUE;
+  }
+
+  return FALSE;
+}
+
 STATIC CONST EFI_PEI_PPI_DESCRIPTOR  mTpm2DiscoveredPpi = {
   EFI_PEI_PPI_DESCRIPTOR_PPI | EFI_PEI_PPI_DESCRIPTOR_TERMINATE_LIST,
   &gOvmfTpmDiscoveredPpiGuid,
@@ -56,6 +108,9 @@ PlatformPeim (
   CONST UINT32              *RangesProp;
   UINT64                    TpmBase;
   EFI_STATUS                Status;
+  CHAR8                     DebugLevelBuf[32];
+  UINTN                     DebugLevelBufSize;
+  CONST CHAR8               *DebugLevelStr;
 
   Base = (VOID *)(UINTN)PcdGet64 (PcdDeviceTreeInitialBaseAddress);
   ASSERT (Base != NULL);
@@ -124,6 +179,23 @@ PlatformPeim (
       ));
   }
 
+  DebugLevelBufSize = sizeof (DebugLevelBuf);
+  Status            = QemuFwCfgGetAsString (
+                        "opt/org.tianocore/DebugLevel",
+                        &DebugLevelBufSize,
+                        DebugLevelBuf
+                        );
+  if (!RETURN_ERROR (Status)) {
+    DebugLevelStr = DebugLevelBuf;
+  } else {
+    DebugLevelStr = (CONST CHAR8 *)PcdGetPtr (PcdSerialDebugPrintErrorLevel);
+  }
+
+  UartHobData->DebugLevelSet = ParseSerialDebugLevel (
+                                 DebugLevelStr,
+                                 &UartHobData->DebugLevel
+                                 );
+
   TpmBase = 0;
 
   //

ArmVirtPkg/Library/PlatformPeiLib/PlatformPeiLib.inf

@@ -30,6 +30,7 @@
   gArmVirtTokenSpaceGuid.PcdTpm2SupportEnabled
 
 [LibraryClasses]
+  BaseLib
   BaseMemoryLib
   DebugLib
   HobLib
@@ -37,9 +38,11 @@
   FdtSerialPortAddressLib
   PcdLib
   PeiServicesLib
+  QemuFwCfgSimpleParserLib
 
 [FixedPcd]
   gArmTokenSpaceGuid.PcdFvSize
+  gArmVirtTokenSpaceGuid.PcdSerialDebugPrintErrorLevel
   gUefiOvmfPkgTokenSpaceGuid.PcdDeviceTreeAllocationPadding
 
 [Pcd]