Re: [edk2-devel] [PATCH edk2-platforms 3/5] Platform/RaspberryPi: fix 16550 divisor calculation logic

[Ard Biesheuvel]

On 5/6/20 12:18 PM, Pete Batard wrote:
One general remark below:
On 2020.05.05 19:10, Ard Biesheuvel wrote:
On 5/5/20 4:50 PM, Ard Biesheuvel wrote:
The 16550 'miniUART' on the Raspberry Pi gets its input clock from
different sources on RPi3 and RPi3. Fix the logic that derives the

This should be 'Rpi3 and RPi4'

divisor for the 16550 baud clock on the respective platforms.

While at it, make the input clock PCD patchable for RPi3 so we can
manipulate it at runtime in a future patch.

For the sake of harmonization between platforms, wouldn't we want to 
also declare the PCD patchable on RPi4 as well (even though we obviously 
aren't going to patch it for the time being)?


I'd prefer not to. That way, we can easily spot problems when the 
patching code is incorporated inadvertently.

There is some plan of factorizing the DSC content, so if that doesn't 
hurt us, I'd propose we try to keep the Pi3 and Pi4 version as close as 
possible.

This also ties in with my remark for the next patch.


Co-authored-by: Pete Batard <p...@akeo.ie>
Co-authored-by: Andrei Warkentin <andrey.warken...@gmail.com>
Co-authored-by: Ard Biesheuvel <ard.biesheu...@arm.com>
Signed-off-by: Pete Batard <p...@akeo.ie>
Signed-off-by: Ard Biesheuvel <ard.biesheu...@arm.com>
---
  Platform/RaspberryPi/RPi3/RPi3.dsc |  4 +++-
  Platform/RaspberryPi/RPi4/RPi4.dsc |  2 +-
  Platform/RaspberryPi/Library/DualSerialPortLib/DualSerialPortLib.c 
| 14 ++++++++------
  3 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/Platform/RaspberryPi/RPi3/RPi3.dsc 
b/Platform/RaspberryPi/RPi3/RPi3.dsc
index d7218219fc5a..96b27400eef8 100644
--- a/Platform/RaspberryPi/RPi3/RPi3.dsc
+++ b/Platform/RaspberryPi/RPi3/RPi3.dsc
@@ -409,7 +409,6 @@ [PcdsFixedAtBuild.common]
    gArmPlatformTokenSpaceGuid.PL011UartClkInHz|48000000
    gEfiMdeModulePkgTokenSpaceGuid.PcdSerialUseMmio|TRUE
    gEfiMdeModulePkgTokenSpaceGuid.PcdSerialRegisterStride|4
-  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialClockRate|500000000
    gEfiMdeModulePkgTokenSpaceGuid.PcdSerialFifoControl|0x27
    gEfiMdeModulePkgTokenSpaceGuid.PcdSerialExtendedTxFifoSize|8
    gEfiMdePkgTokenSpaceGuid.PcdUartDefaultBaudRate|115200
@@ -441,6 +440,9 @@ [PcdsFixedAtBuild.common]
    gEfiMdeModulePkgTokenSpaceGuid.PcdFirmwareVendor|L"EDK2"
    gEfiMdeModulePkgTokenSpaceGuid.PcdSetNxForStack|TRUE
+[PcdsPatchableInModule]
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialClockRate|250000000
+
  [PcdsDynamicHii.common.DEFAULT]
    #
diff --git a/Platform/RaspberryPi/RPi4/RPi4.dsc 
b/Platform/RaspberryPi/RPi4/RPi4.dsc
index 4fb015b077e6..5d8bd88d7e34 100644
--- a/Platform/RaspberryPi/RPi4/RPi4.dsc
+++ b/Platform/RaspberryPi/RPi4/RPi4.dsc
@@ -420,7 +420,7 @@ [PcdsFixedAtBuild.common]
    gArmPlatformTokenSpaceGuid.PL011UartClkInHz|48000000
    gEfiMdeModulePkgTokenSpaceGuid.PcdSerialUseMmio|TRUE
    gEfiMdeModulePkgTokenSpaceGuid.PcdSerialRegisterStride|4
-  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialClockRate|500000000
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialClockRate|1000000000
    gEfiMdeModulePkgTokenSpaceGuid.PcdSerialFifoControl|0x27
    gEfiMdeModulePkgTokenSpaceGuid.PcdSerialExtendedTxFifoSize|8
    gEfiMdePkgTokenSpaceGuid.PcdUartDefaultBaudRate|115200
diff --git 
a/Platform/RaspberryPi/Library/DualSerialPortLib/DualSerialPortLib.c 
b/Platform/RaspberryPi/Library/DualSerialPortLib/DualSerialPortLib.c
index b1d17d3fa04a..5e83bbf022eb 100644
--- a/Platform/RaspberryPi/Library/DualSerialPortLib/DualSerialPortLib.c
+++ b/Platform/RaspberryPi/Library/DualSerialPortLib/DualSerialPortLib.c
@@ -41,18 +41,20 @@ SerialPortGetDivisor (
    // On the Raspberry Pi, the clock to use for the 16650-compatible 
UART
    // is the base clock divided by the 12.12 fixed point VPU clock 
divisor.
    //
-  BaseClockRate = (UINT64)PcdGet32 (PcdSerialClockRate) * 4;
+  BaseClockRate = (UINT64)PcdGet32 (PcdSerialClockRate);
+#if (RPI_MODEL == 4)
    Divisor = MmioRead32(BCM2836_CM_BASE + 
BCM2836_CM_VPU_CLOCK_DIVISOR) & 0xFFFFFF;
    if (Divisor != 0)
      BaseClockRate = (BaseClockRate << 12) / Divisor;
+#endif
    //
-  // Now calculate divisor for baud generator
-  //    Ref_Clk_Rate / Baud_Rate / 16
+  // As per the BCM2xxx datasheets:
+  // baudrate = system_clock_freq / (8 * (divisor + 1)).
    //
-  Divisor = (UINT32)BaseClockRate / (SerialBaudRate * 16);
-  if (((UINT32)BaseClockRate % (SerialBaudRate * 16)) >= 
SerialBaudRate * 8) {
-    Divisor++;
+  Divisor = (UINT32)BaseClockRate / (SerialBaudRate * 8);
+  if (Divisor != 0) {
+    Divisor--;
    }
    return Divisor;
  }






Reviewed-by: Pete Batard <p...@akeo.ie>



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