Re: [edk2-devel] [PATCH] ArmPlatformPkg/PL011UartLib: Add PCD for FIFO depth

["Ard Biesheuvel" <ard.biesheuvel@arm.com>]

On 6/6/20 5:23 AM, Irene Park via groups.io wrote:
> From: Irene Park <ipark@nvidia.com>
> 
> PL011UartLib determines its FIFO depth based on the PID2 value but
> the register PID2 is not mandatory in the SBSA spec.
> This change adds a new 32bit PCD reference to define a FIFO depth and
> make PL011UartLib available for the custom UART which is compliant
> to the SBSA spec but doesn't support the optional register of PID2.
> 

What does 'doesn't support' mean in this case?

> * Available values for PL011UartFifoDepth: 0, 16, 32
> 
> Note that a FIFO depth will be determined based on PID2 when the PCD
> reference is set to 0.
> 
> Signed-off-by: Irene Park <ipark@nvidia.com>
> ---
>   ArmPlatformPkg/ArmPlatformPkg.dec                    | 2 ++
>   ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.c   | 4 ++++
>   ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.inf | 1 +
>   3 files changed, 7 insertions(+)
> 
> diff --git a/ArmPlatformPkg/ArmPlatformPkg.dec b/ArmPlatformPkg/ArmPlatformPkg.dec
> index 696d636..b4b950f 100644
> --- a/ArmPlatformPkg/ArmPlatformPkg.dec
> +++ b/ArmPlatformPkg/ArmPlatformPkg.dec
> @@ -72,6 +72,8 @@
>     gArmPlatformTokenSpaceGuid.PL011UartFractional|0|UINT32|0x0000002D
>     gArmPlatformTokenSpaceGuid.PL011UartInterrupt|0x00000000|UINT32|0x0000002F
>     gArmPlatformTokenSpaceGuid.PL011UartRegOffsetVariant|0|UINT8|0x0000003E
> +  ## FIFO Depth in 0/16/32 (0 to determine FIFO depth based on PID2)
> +  gArmPlatformTokenSpaceGuid.PL011UartFifoDepth|0|UINT32|0x0000003F
>   
>     ## PL011 Serial Debug UART
>     gArmPlatformTokenSpaceGuid.PcdSerialDbgRegisterBase|0x00000000|UINT64|0x00000030
> diff --git a/ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.c b/ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.c
> index 801990d..1aa6830 100644
> --- a/ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.c
> +++ b/ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.c
> @@ -79,9 +79,13 @@ PL011UartInitializePort (
>     UINT32      Fractional;
>     UINT32      HardwareFifoDepth;
>   
> +  HardwareFifoDepth = FixedPcdGet8 (PL011UartFifoDepth);
> +#if FixedPcdGet8 (PL011UartFifoDepth) == 0
>     HardwareFifoDepth = (PL011_UARTPID2_VER (MmioRead32 (UartBase + UARTPID2)) \
>                          > PL011_VER_R1P4) \
>                         ? 32 : 16 ;
> +#endif
> +
>     // The PL011 supports a buffer of 1, 16 or 32 chars. Therefore we can accept
>     // 1 char buffer as the minimum FIFO size. Because everything can be rounded
>     // down, there is no maximum FIFO size.
> diff --git a/ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.inf b/ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.inf
> index d99e89f..3e5efc7 100644
> --- a/ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.inf
> +++ b/ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.inf
> @@ -35,3 +35,4 @@
>     gArmPlatformTokenSpaceGuid.PL011UartInteger
>     gArmPlatformTokenSpaceGuid.PL011UartFractional
>     gArmPlatformTokenSpaceGuid.PL011UartRegOffsetVariant
> +  gArmPlatformTokenSpaceGuid.PL011UartFifoDepth
>