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

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

On 5/6/20 12:18 PM, Pete Batard wrote:
> 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?
> 

We should add it, but we can add it to the [Pcd] section.

Alternatively, we could have different .INFs for RPi3 and RPi4, but that 
is really overkill IMO.

Making it patchable on both platforms just to patch it on one is also 
unnecessary I think. The current approach will ensure that we catch any 
issues at build time, without any major hacks,].

> 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"...
> 

We don't actually need the adrp/str pair with the lo12 here, I will 
replace it with adr. (Just muscle memory)



>>>       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>
> 


Thanks