Re: [edk2-devel] [PATCH v3 09/39] MdePkg: Add a new library named PeiServicesTablePointerLibReg

["Chao Li" <lichao@loongson.cn>]

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Hi Mike and Liming,

Ping for review, I'd love to know your opinion, as the last email saied, 
your opinion can decide the direction, so please review the new patches 
of MdePkg for this series, please...


Thanks,
Chao
On 2023/11/27 11:27, Chao Li wrote:
>
> Hi Mike and Liming,
>
> You opinion is very important, it will decide the direction. I will 
> send the V4 this week, so can you please review the new patch of 
> MdePkg for this series?
>
> On 2023/11/24 19:35, Laszlo Ersek wrote:
>> On 11/22/23 02:47, Chao Li wrote:
>>> Hi Laszlo,
>>>
>>>
>>> Thanks,
>>> Chao
>>> On 2023/11/21 22:37, Laszlo Ersek wrote:
>>>> On 11/17/23 10:59, Chao Li wrote:
>>>>> Since some ARCH or platform not require execute code on memory during
>>>>> PEI phase, some values may transferred via CPU registers.
>>>>>
>>>>> Adding PeiServcieTablePointerLibReg to allow set and get the PEI service
>>>>> table pointer depend by a CPU register, this library can accommodate lot
>>>>> of platforms who not require execte code on memory during PEI phase.
>>>>>
>>>>> Adding PeiServiceTablePointerLibReg to allows setting and getting the
>>>>> PEI service table pointer via CPU registers, and the library can
>>>>> accommodate many platforms that do not need to execute code on memory
>>>>> during the PEI phase.
>>>>>
>>>>> The idea of this library is derived from
>>>>> ArmPkg/Library/PeiServicesTablePointerLib/
>>>>>
>>>>> BZ:https://bugzilla.tianocore.org/show_bug.cgi?id=4584
>>>>>
>>>>> Cc: Michael D Kinney<michael.d.kinney@intel.com>
>>>>> Cc: Liming Gao<gaoliming@byosoft.com.cn>
>>>>> Cc: Zhiguang Liu<zhiguang.liu@intel.com>
>>>>> Cc: Leif Lindholm<quic_llindhol@quicinc.com>
>>>>> Cc: Ard Biesheuvel<ardb+tianocore@kernel.org>
>>>>> Cc: Sami Mujawar<sami.mujawar@arm.com>
>>>>> Cc: Laszlo Ersek<lersek@redhat.com>
>>>>> Cc: Sunil V L<sunilvl@ventanamicro.com>
>>>>> Signed-off-by: Chao Li<lichao@loongson.cn>
>>>>> ---
>>>>>   .../Library/PeiServicesTablePointerLib.h      | 37 +++++++-
>>>>>   .../PeiServicesTablePointer.c                 | 86 +++++++++++++++++++
>>>>>   .../PeiServicesTablePointerLib.uni            | 20 +++++
>>>>>   .../PeiServicesTablePointerLibReg.inf         | 40 +++++++++
>>>>>   MdePkg/MdePkg.dsc                             |  1 +
>>>>>   5 files changed, 180 insertions(+), 4 deletions(-)
>>>>>   create mode 100644 MdePkg/Library/PeiServicesTablePointerLibReg/PeiServicesTablePointer.c
>>>>>   create mode 100644 MdePkg/Library/PeiServicesTablePointerLibReg/PeiServicesTablePointerLib.uni
>>>>>   create mode 100644 MdePkg/Library/PeiServicesTablePointerLibReg/PeiServicesTablePointerLibReg.inf
>>>> In my opinion, the PeiServicesTablePointerLib class header should not be
>>>> extended with new interfaces. I understand that the generality is
>>>> attractive, but it is not put to use; only the loongarch architecture
>>>> applies the new interfaces (in the subsequent patch), and for example
>>>> the ARM code (ArmPkg/Library/PeiServicesTablePointerLib) is not reworked
>>>> in terms of these new interfaces.
>>> This libarary have ability of accommodate more ARCH why not? I checked
>>> the PI SPEC, all ARCH except IA32 and X64 using the register mechanism,
>>> if this library can be approved, all of them can moved into this
>>> libraryso that code con be reused more, I think this library is fine.
>> The library may be fine from a design point of view, but without
>> actually putting the extra generality to use, it's a waste. It's a
>> maintenance burden. There's a name for this anti-pattern: it is called
>> "speculative generality". "It might be useful down the road."
>>
>> The new generality is only useful if it carries its own weight; namely,
>> if other platform code (aarch64, x64) is converted to it immediately, in
>> the same series. (I'm not asking for this series to be longer. You could
>> even split it up into multiple "waves" of series.) Just saying that
>> "could prove useful later" is a prime way to generate technical debt.
>>
>>>> What's more, the new library interfaces, even though they are exposed in
>>>> the lib class header, are not implemented for other architectures, so
>>>> they aren't even callable on those arches.
>>> The patch 10 in this series has added LoongArch instance of this
>>> library, please check.
>> Yes, I'm aware. That's not the point.
>>
>> When you extend a library *class* with a new API, that means all
>> *clients* of the library class can stat calling that API. Which in turn
>> means that *all* existent instances of the library class must implement
>> the API as well.
>>
>> Your series extends the lib class with a new API, but (IIUC) only
>> implements the new API in one (new) lib instance, and not in the other
>> (existent) instances. This has the potential to cause linkage errors,
>> dependent on the actual library instance that a platform DSC chooses.
>>
>>
>>>> I'm commenting on this patch and the subsequent patch in the series
>>>> together, as seen squashed together. NB I'm not an MdePkg maintainer, so
>>>> this is just my opinion.
>>> So, Mike and Liming, what do your think?
>>>> (1) As noted above, the library class should not be modified.
>>>>
>>>> (2) Modifying the *comments* in
>>>> "MdePkg/Include/Library/PeiServicesTablePointerLib.h" is welcome, I
>>>> think, but then we might want to add a (separate!) patch for removing
>>>> the Itanium language, as edk2 no longer supports Itanium.
>>>>
>>>> (3) The PeiServicesTablePointerLibReg instance should be called
>>>> PeiServicesTablePointerLibCsrKs0 or just PeiServicesTablePointerLibKs0.
>>> This library will be a public libray which using the reigster mechanism,
>>> so the name like PeiServiceTablePointerLibCsrKs0 would not appropriate.
>> Of course that name is wrong for a generic library instance, but my
>> whole point is that this library instance should be loongarch-specific.
>>
>> (Unless you port the existent (x64 IDT / aarch64 register) libraries
>> over to it.)
>>
>>>> This follows the example of the lib instance name
>>>> "PeiServicesTablePointerLibIdt". The whole library instance should be
>>>> loongaarch-specific IMO; there isn't much code that's being duplicated,
>>>> so the extra interfaces (internal or external) do not help with code
>>>> unification.
>>>>
>>>> (4) "PeiServicesTablePointerLib.uni" should be named similarly (suffix
>>>> missing).
>>>>
>>>> (5) BASE_NAME in the library instance INF file should be defined
>>>> similarly (suffix missing).
>>>>
>>>> (6) The contents of the UNI file should be loongarch-specific, i.e. be
>>>> explicit about CSR KS0, in both comments and string constants.
>>>>
>>>> (7) The comments in the library instance INF file should be similarly
>>>> loongarch-specific.
>>>>
>>>> (8) I suggest dropping VALID_ARCHITECTURES altogether. If we want to
>>>> keep it, it should exclusively say LOONGARCH64.
>>>>
>>>> (9) The new library instance should be listed in
>>>> [Components.LOONGARCH64] in MdePkg.dec.
>>>>
>>>> This section does not exist yet; I suggest introducing it under
>>>> [Components.RISCV64].
>>> No, it is RISC-V area, not LOONGARCH64.
>> You misunderstood.
>>
>> I didn't suggest to list the *library instance* under [Components.RISCV64].
>>
>> I suggested to introduce the [Components.LOONGARCH64] *section* under
>> [Components.RISCV64].
>>
>>> And I do not recommend going
>>> this way. I believe this library should be a public library for register
>>> mechanism.
>> That's entirely fine, as long as you do the work of porting the existent
>> ARM and X64 IDT code over to it. In my opinion anyway; MdePkg
>> maintainers are the authoritative sources here.
>>
>> Laszlo
>>
>>>> (10) There need not / should not be two separate C source files; just
>>>> access the KS0 CSR in SetPeiServicesTablePointer() and
>>>> GetPeiServicesTablePointer() directly.
>>>>
>>>> (11) The new library instance should probably not introduce new
>>>> references to Itanium.
>>>>
>>>> Thanks,
>>>> Laszlo
> 


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