[edk2-platforms][PATCH 4/6] Platform/RPi4: Add switch to select between PL011 and miniUART

["Pete Batard" <pete@akeo.ie>]

The PL011 can be a better choice for the serial console on the RPi4,
given that its baud clock is not derived from the CPU clock (which
may change under our feet unless we keep it fixed at a low rate), and
given the fact that the SBSA/SBBR specs that describe ARM specific
architectural requirements for ACPI only permit PL011 based UARTs to
begin with.

Therefore we add a new PL011_ENABLE build switch to tell the firmware
to use PL011 for all console serial I/O, including for TF-A, SPCR and
DBG2, as well as toggle the BlueTooth module to use the mini UART.

For the time being, the option is disabled by default because it
requires an overlay to be enabled in config.txt that pinmuxes the
PL011 TX/RX lines to the UART pins on the connector block.

Signed-off-by: Pete Batard <pete@akeo.ie>
---
 Platform/RaspberryPi/RPi4/AcpiTables/Dbg2.aslc | 10 +++++
 Platform/RaspberryPi/RPi4/AcpiTables/Spcr.aslc |  9 +++-
 Platform/RaspberryPi/RPi4/AcpiTables/Uart.asl  |  6 ++-
 Platform/RaspberryPi/RPi4/RPi4.dsc             | 23 +++++++++++
 Platform/RaspberryPi/RPi4/RPi4.fdf             |  4 ++
 Platform/RaspberryPi/RPi4/Readme.md            | 43 ++++++++++++++++----
 6 files changed, 84 insertions(+), 11 deletions(-)

diff --git a/Platform/RaspberryPi/RPi4/AcpiTables/Dbg2.aslc b/Platform/RaspberryPi/RPi4/AcpiTables/Dbg2.aslc
index 589a5c2cbd71..e408eb02d027 100644
--- a/Platform/RaspberryPi/RPi4/AcpiTables/Dbg2.aslc
+++ b/Platform/RaspberryPi/RPi4/AcpiTables/Dbg2.aslc
@@ -22,6 +22,11 @@
 #define RPI_DBG2_NUMBER_OF_GENERIC_ADDRESS_REGISTERS    1
 #define RPI_DBG2_NAMESPACESTRING_FIELD_SIZE             10
 
+#ifdef PL011_ENABLE
+#define RPI_UART_BASE_ADDRESS                           FixedPcdGet64 (PcdSerialRegisterBase)
+#define RPI_UART_LENGTH                                 0x1000
+#define RPI_UART_STR                                    { '\\', '_', 'S', 'B', '.', 'U', 'R', 'T', '0', 0x00 }
+#else
 //
 // When using the miniUART, PcdSerialRegisterBase points to the 8250 base address,
 // which is offset by 0x40 from the actual Bcm2835 base address
@@ -32,6 +37,7 @@
 // RPI_UART_STR should match the value used Uart.asl
 //
 #define RPI_UART_STR                                    { '\\', '_', 'S', 'B', '.', 'U', 'R', 'T', 'M', 0x00 }
+#endif
 
 typedef struct {
   EFI_ACPI_DBG2_DEBUG_DEVICE_INFORMATION_STRUCT         Dbg2Device;
@@ -83,7 +89,11 @@ STATIC DBG2_TABLE Dbg2 = {
      */
     DBG2_DEBUG_PORT_DDI (
       RPI_DBG2_NUMBER_OF_GENERIC_ADDRESS_REGISTERS,
+#ifdef PL011_ENABLE
+      EFI_ACPI_DBG2_PORT_SUBTYPE_SERIAL_ARM_PL011_UART,
+#else
       EFI_ACPI_DBG2_PORT_SUBTYPE_SERIAL_BCM2835_UART,
+#endif
       RPI_UART_BASE_ADDRESS,
       RPI_UART_LENGTH,
       RPI_UART_STR
diff --git a/Platform/RaspberryPi/RPi4/AcpiTables/Spcr.aslc b/Platform/RaspberryPi/RPi4/AcpiTables/Spcr.aslc
index 65f48ceae688..e5c10c923626 100644
--- a/Platform/RaspberryPi/RPi4/AcpiTables/Spcr.aslc
+++ b/Platform/RaspberryPi/RPi4/AcpiTables/Spcr.aslc
@@ -18,12 +18,19 @@
 
 #define RPI_UART_FLOW_CONTROL_NONE           0
 
+#ifdef PL011_ENABLE
+#define RPI_UART_INTERFACE_TYPE              EFI_ACPI_SERIAL_PORT_CONSOLE_REDIRECTION_TABLE_INTERFACE_TYPE_ARM_PL011_UART
+#define RPI_UART_BASE_ADDRESS                FixedPcdGet64 (PcdSerialRegisterBase)
+#define RPI_UART_INTERRUPT                   0x99
+#else
+#define RPI_UART_INTERFACE_TYPE              EFI_ACPI_SERIAL_PORT_CONSOLE_REDIRECTION_TABLE_INTERFACE_TYPE_BCM2835_UART
 //
 // When using the miniUART, PcdSerialRegisterBase points to the 8250 base address,
 // which is offset by 0x40 from the actual Bcm2835 base address
 //
 #define RPI_UART_BASE_ADDRESS                (FixedPcdGet64 (PcdSerialRegisterBase) - 0x40)
 #define RPI_UART_INTERRUPT                   0x7D
+#endif
 
 STATIC EFI_ACPI_SERIAL_PORT_CONSOLE_REDIRECTION_TABLE Spcr = {
   ACPI_HEADER (
@@ -32,7 +39,7 @@ STATIC EFI_ACPI_SERIAL_PORT_CONSOLE_REDIRECTION_TABLE Spcr = {
     EFI_ACPI_SERIAL_PORT_CONSOLE_REDIRECTION_TABLE_REVISION
   ),
   // UINT8                                   InterfaceType;
-  EFI_ACPI_SERIAL_PORT_CONSOLE_REDIRECTION_TABLE_INTERFACE_TYPE_BCM2835_UART,
+  RPI_UART_INTERFACE_TYPE,
   // UINT8                                   Reserved1[3];
   {
     EFI_ACPI_RESERVED_BYTE,
diff --git a/Platform/RaspberryPi/RPi4/AcpiTables/Uart.asl b/Platform/RaspberryPi/RPi4/AcpiTables/Uart.asl
index 15149892f3b0..5b59f2dd3e16 100644
--- a/Platform/RaspberryPi/RPi4/AcpiTables/Uart.asl
+++ b/Platform/RaspberryPi/RPi4/AcpiTables/Uart.asl
@@ -108,7 +108,7 @@ Device(BTH0)
   {
     Name (RBUF, ResourceTemplate ()
     {
-      // BT UART: UART0 (PL011)
+      // BT UART: URT0 (PL011) or URTM (miniUART)
       UARTSerialBus(
         115200,        // InitialBaudRate: in BPS
         ,              // BitsPerByte: default to 8 bits
@@ -133,7 +133,11 @@ Device(BTH0)
                        //   no flow control.
         16,            // ReceiveBufferSize
         16,            // TransmitBufferSize
+#ifdef PL011_ENABLE
+        "\\_SB.URTM",  // ResourceSource:
+#else
         "\\_SB.URT0",  // ResourceSource:
+#endif
                        //   UART bus controller name
         ,              // ResourceSourceIndex: assumed to be 0
         ,              // ResourceUsage: assumed to be
diff --git a/Platform/RaspberryPi/RPi4/RPi4.dsc b/Platform/RaspberryPi/RPi4/RPi4.dsc
index 1624ebda27d7..ccf5bd5b9ef3 100644
--- a/Platform/RaspberryPi/RPi4/RPi4.dsc
+++ b/Platform/RaspberryPi/RPi4/RPi4.dsc
@@ -38,6 +38,7 @@ [Defines]
   DEFINE SECURE_BOOT_ENABLE      = FALSE
   DEFINE INCLUDE_TFTP_COMMAND    = FALSE
   DEFINE DEBUG_PRINT_ERROR_LEVEL = 0x8000004F
+  DEFINE PL011_ENABLE            = FALSE
 
 ################################################################################
 #
@@ -116,10 +117,16 @@ [LibraryClasses.common]
   ArmHvcLib|ArmPkg/Library/ArmHvcLib/ArmHvcLib.inf
   ArmGenericTimerCounterLib|ArmPkg/Library/ArmGenericTimerPhyCounterLib/ArmGenericTimerPhyCounterLib.inf
 
+!if $(PL011_ENABLE) == TRUE
+  PL011UartClockLib|ArmPlatformPkg/Library/PL011UartClockLib/PL011UartClockLib.inf
+  PL011UartLib|ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.inf
+  SerialPortLib|ArmPlatformPkg/Library/PL011SerialPortLib/PL011SerialPortLib.inf
+!else
   PciCf8Lib|MdePkg/Library/BasePciCf8Lib/BasePciCf8Lib.inf
   PciLib|MdePkg/Library/BasePciLibCf8/BasePciLibCf8.inf
   PlatformHookLib|MdeModulePkg/Library/BasePlatformHookLibNull/BasePlatformHookLibNull.inf
   SerialPortLib|MdeModulePkg/Library/BaseSerialPortLib16550/BaseSerialPortLib16550.inf
+!endif
 
   # Cryptographic libraries
   IntrinsicLib|CryptoPkg/Library/IntrinsicLib/IntrinsicLib.inf
@@ -229,6 +236,12 @@ [BuildOptions]
   GCC:*_*_AARCH64_DLINK_FLAGS = -Wl,--fix-cortex-a53-843419
   GCC:RELEASE_*_*_CC_FLAGS    = -DMDEPKG_NDEBUG -DNDEBUG
 
+!if $(PL011_ENABLE) == TRUE
+  GCC:*_*_*_CC_FLAGS          = -DPL011_ENABLE
+  GCC:*_*_*_ASLPP_FLAGS       = -DPL011_ENABLE
+  GCC:*_*_*_ASLCC_FLAGS       = -DPL011_ENABLE
+!endif
+
 [BuildOptions.common.EDKII.DXE_RUNTIME_DRIVER]
   GCC:*_*_AARCH64_DLINK_FLAGS = -z common-page-size=0x10000
 
@@ -391,6 +404,13 @@ [PcdsFixedAtBuild.common]
   gBcm27xxTokenSpaceGuid.PcdBcm27xxPciBusMmioLen|0x3ffffff
   gBcm27xxTokenSpaceGuid.PcdBcm27xxPciCpuMmioAdr|0x600000000
 
+!if $(PL011_ENABLE) == TRUE
+  ## PL011 UART
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialRegisterBase|0xfe201000
+  gArmPlatformTokenSpaceGuid.PL011UartInteger|0
+  gArmPlatformTokenSpaceGuid.PL011UartFractional|0
+  gArmPlatformTokenSpaceGuid.PL011UartClkInHz|48000000
+!else
   ## NS16550 compatible UART
   gEfiMdeModulePkgTokenSpaceGuid.PcdSerialRegisterBase|0xfe215040
   gEfiMdeModulePkgTokenSpaceGuid.PcdSerialUseMmio|TRUE
@@ -398,7 +418,10 @@ [PcdsFixedAtBuild.common]
   gEfiMdeModulePkgTokenSpaceGuid.PcdSerialClockRate|500000000
   gEfiMdeModulePkgTokenSpaceGuid.PcdSerialFifoControl|0x27
   gEfiMdeModulePkgTokenSpaceGuid.PcdSerialExtendedTxFifoSize|8
+!endif
+
   gEfiMdePkgTokenSpaceGuid.PcdUartDefaultBaudRate|115200
+  gEfiMdePkgTokenSpaceGuid.PcdUartDefaultReceiveFifoDepth|0
 
   #
   # ARM General Interrupt Controller
diff --git a/Platform/RaspberryPi/RPi4/RPi4.fdf b/Platform/RaspberryPi/RPi4/RPi4.fdf
index 7a506bd2813b..50fe554ec9ec 100644
--- a/Platform/RaspberryPi/RPi4/RPi4.fdf
+++ b/Platform/RaspberryPi/RPi4/RPi4.fdf
@@ -51,7 +51,11 @@ [FD.RPI_EFI]
 # ATF primary boot image
 #
 0x00000000|0x00020000
+!if $(PL011_ENABLE) == TRUE
+FILE = Platform/RaspberryPi/$(PLATFORM_NAME)/TrustedFirmware/bl31_pl011.bin
+!else
 FILE = Platform/RaspberryPi/$(PLATFORM_NAME)/TrustedFirmware/bl31_miniuart.bin
+!endif
 
 #
 # DTB.
diff --git a/Platform/RaspberryPi/RPi4/Readme.md b/Platform/RaspberryPi/RPi4/Readme.md
index 2e37646e043d..2ef38d1b2062 100644
--- a/Platform/RaspberryPi/RPi4/Readme.md
+++ b/Platform/RaspberryPi/RPi4/Readme.md
@@ -18,13 +18,21 @@ following __major__ limitations:
 
 - USB is likely to work only in pre-OS phase at this stage (nonstandard ECAM,
   missing ACPI tables).
-- Serial I/O from the OS may not work at all due to CPU throttling affecting
-  the miniUART baudrate.
+- Serial I/O from the OS may not work due to CPU throttling affecting the
+  miniUART baudrate. This can be worked around by using the `PL011_ENABLE`
+  compilation option.
 
 # Building
 
 Build instructions from the top level edk2-platforms Readme.md apply.
 
+The following additional build options are also available:
+- `-D PL011_ENABLE=1`: Selects PL011 for the serial console instead of the
+  miniUART (default). This doesn't change the GPIO pinout for the UART but
+  can be useful if you find that the miniUART baud rate changes when the
+  OS throttles the CPU. Note that this requires one of `disable-bt.dtbo` or
+  `miniuart-bt.dtbo` overlays to have been applied (see below).
+
 # Booting the firmware
 
 1. Format a uSD card as FAT16 or FAT32
@@ -33,14 +41,31 @@ Build instructions from the top level edk2-platforms Readme.md apply.
   - `bcm2711-rpi-4-b.dtb`
   - `fixup4.dat`
   - `start4.elf`
+  - `overlays/miniuart-bt.dbto` or `overlays/disable-bt.dtbo` (Optional)
 4. Create a `config.txt` with the following content:
-  ```
-  arm_64bit=1
-  enable_uart=1
-  core_freq=250
-  enable_gic=1
-  armstub=RPI_EFI.fd
-  ```
+  - For a firmware **without** the `PL011_ENABLE` build option:
+    ```
+    arm_64bit=1
+    enable_uart=1
+    core_freq=250
+    enable_gic=1
+    armstub=RPI_EFI.fd
+    disable_commandline_tags=1
+    ```
+  - For a firmware **with** the `PL011_ENABLE` build option:
+    ```
+    arm_64bit=1
+    enable_gic=1
+    armstub=RPI_EFI.fd
+    disable_commandline_tags=1
+    device_tree_address=0x20000
+    device_tree_end=0x30000
+    device_tree=bcm2711-rpi-4-b.dtb
+    dtoverlay=miniuart-bt
+    ```
+    The abobe also requires `miniuart-bt.dbto` to have been copied into an `overlays/`
+    directory on the uSD card. Alternatively, you may use `disable-bt` instead of
+    `miniuart-bt` if you don't require BlueTooth.
 5. Insert the uSD card and power up the Pi.
 
 # Notes
-- 
2.21.0.windows.1