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

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

One remark below:

On 2020.05.05 19:11, Ard Biesheuvel wrote:
> 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
>> +

Since we're modifying a patchable PCD here, shouldn't we add a:

[PatchPcd]
   gEfiMdeModulePkgTokenSpaceGuid.PcdSerialClockRate

section in PlatformLib.inf?

Of course, if we do that, we can't keep PcdSerialClockRate fixed for 
RPi4, as the build process will complain about PCD mismatch.

I also wouldn't mind a comment that explains how one arrives at figuring 
out that "_gPcd_BinaryPatch_PcdSerialClockRate" should be used to locate 
our address (and possibly the addition of :lo12:), because I don't think 
it's going to be that straightforward for people reading the code for 
the first time, though I fear that the explanation will boil down to "we 
need to do it this specific way for a gcc aarch64 relocation"...

>>       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
>>
> 
> 
> 
> 

With addition of "GCC:*_*_*_PP_FLAGS = -DRPI_MODEL=3" in the .dsc:
Reviewed-by: Pete Batard <pete@akeo.ie>