Re: [PATCH edk2-platforms 4/5] Platform/RaspberryPi3: query firmware for 16550 input clock at boot

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

On 5/5/20 4:50 PM, Ard Biesheuvel wrote:
> Query the firmware for the clock rate that is used to drive the
> 16550 baud clock, so that we can program the correct baud rate.
> 
> Co-authored-by: Pete Batard <pete@akeo.ie>
> Co-authored-by: Andrei Warkentin <andrey.warkentin@gmail.com>
> Co-authored-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
> Signed-off-by: Pete Batard <pete@akeo.ie>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
> ---
>   Platform/RaspberryPi/Library/PlatformLib/AArch64/RaspberryPiHelper.S | 25 +++++++++++++++++++-
>   1 file changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/Platform/RaspberryPi/Library/PlatformLib/AArch64/RaspberryPiHelper.S b/Platform/RaspberryPi/Library/PlatformLib/AArch64/RaspberryPiHelper.S
> index 91dfe1bb981e..35580e4ed73a 100644
> --- a/Platform/RaspberryPi/Library/PlatformLib/AArch64/RaspberryPiHelper.S
> +++ b/Platform/RaspberryPi/Library/PlatformLib/AArch64/RaspberryPiHelper.S
> @@ -3,7 +3,7 @@
>    *  Copyright (c) 2020, Andrei Warkentin <andrey.warkentin@gmail.com>
>    *  Copyright (c) 2019-2020, Pete Batard <pete@akeo.ie>
>    *  Copyright (c) 2016, Linaro Limited. All rights reserved.
> - *  Copyright (c) 2011-2013, ARM Limited. All rights reserved.
> + *  Copyright (c) 2011-2020, ARM Limited. All rights reserved.
>    *
>    *  SPDX-License-Identifier: BSD-2-Clause-Patent
>    *
> @@ -85,6 +85,14 @@ ASM_FUNC (ArmPlatformPeiBootAction)
>       adr     x2, mBoardRevision
>       str     w0, [x2]
>   
> +#if (RPI_MODEL == 3)

As noted by Pete off-list, doing this doesn't work unless we add 
something like

GCC:*_*_*_PP_FLAGS          = -DRPI_MODEL=3

to the [BuildOptions] in RPi3.dsc



> +    run     .Lclkinfo_buffer
> +
> +    ldr     w0, .Lfrequency
> +    adrp    x2, _gPcd_BinaryPatch_PcdSerialClockRate
> +    str     w0, [x2, :lo12:_gPcd_BinaryPatch_PcdSerialClockRate]
> +#endif
> +
>       ret
>   
>       .align  4
> @@ -127,6 +135,21 @@ ASM_FUNC (ArmPlatformPeiBootAction)
>       .long   0                           // end tag
>       .set    .Lrevinfo_size, . - .Lrevinfo_buffer
>   
> +#if (RPI_MODEL == 3)
> +    .align  4
> +.Lclkinfo_buffer:
> +    .long   .Lclkinfo_size
> +    .long   0x0
> +    .long   RPI_MBOX_GET_CLOCK_RATE
> +    .long   8                           // buf size
> +    .long   4                           // input len
> +    .long   4                           // clock id: 0x04 = Core/VPU
> +.Lfrequency:
> +    .long   0                           // frequency
> +    .long   0                           // end tag
> +    .set    .Lclkinfo_size, . - .Lclkinfo_buffer
> +#endif
> +
>   //UINTN
>   //ArmPlatformGetPrimaryCoreMpId (
>   //  VOID
>