On 01/29/15 03:50, Jordan Justen wrote:
> On 2015-01-28 14:38:00, Laszlo Ersek wrote:
>> On 01/28/15 20:01, Jordan Justen wrote:
>>> On 2015-01-28 00:50:43, Laszlo Ersek wrote:
>>>> On 01/28/15 00:29, Jordan Justen wrote:
>>>>> On 2015-01-27 00:17:52, Laszlo Ersek wrote:
>>>>>> On 01/26/15 22:32, Jordan Justen wrote:
>>>>>>> On 2015-01-24 15:04:52, Laszlo Ersek wrote:
>>>>>>>> +EFI_STATUS
>>>>>>>> +EFIAPI
>>>>>>>> +InstallAllQemuLinkedTables (
>>>>>>>> + IN EFI_ACPI_TABLE_PROTOCOL *AcpiProtocol
>>>>>>>> + );
>>>>>>>
>>>>>>> What do you think about moving this to QemuFwCfgLib instead?
>>>>>>
>>>>>> This crossed my mind earlier, but I don't think it's a good idea. Just
>>>>>> because it depends on FwCfg, I don't want to fuse it with the base
>>>>>> library. (Same for QemuBootOrderLib.) ("Base" meaning "foundational",
>>>>>> not "available to all phases", in this context, clearly.)
>>>>>>
>>>>>> (1) Main reason is it makes it harder to port the various independent
>>>>>> features gradually, and/or to port them selectively even for the longer
>>>>>> term.
>>>>>>
>>>>>> A good negative example is the QemuFwCfgS3Enabled() API. Because it was
>>>>>> so small and so easy to implement for OVMF / x86, we fused it with the
>>>>>> QemuFwCfgLib interface. When implementing the library class for ARM
>>>>>> guests, I had no choice but to implement it too (as "return FALSE")
>>>>>> because it had already been part of the interface. The implementation is
>>>>>> quite useless, and worse, nothing at all calls it in
>>>>>> ArmVirtualizationPkg.
>>>>>>
>>>>>>> How about:
>>>>>>> RETURN_STATUS
>>>>>>> EFIAPI
>>>>>>> QemuFwCfgInstallAcpiTables (
>>>>>>> VOID
>>>>>>> );
>>>>>>>
>>>>>>> Obviously this should just assert if called in SEC or PEI.
>>>>>>
>>>>>> I can rename the function if you'd like, but I think build-time (ie.
>>>>>> interface-level) constraints of an API are superior to runtime asserts.
>>>>>> This holds for both different UEFI phases and different architectures.
>>>>>>
>>>>>> You probably don't like the proliferation of small, QEMU-specific
>>>>>> libraries in OVMF. I can appreciate that from an aesthetic POV, but
>>>>>> these features are really this fine-grained, and exposing their
>>>>>> dependencies on the library class level allows me to port them more
>>>>>> flexibly.
>>>>>>
>>>>>> (2) Another reason is that by making the QemuFwCfgLib lib class more
>>>>>> comprehensive, code duplication would worsen. The QemuBootOrderLib and
>>>>>> QemuLoaderLib functionality is identical between ARM and x86. The
>>>>>> underlying fw_cfg access / transfer methods are different.
>>>>>
>>>>> They may be different, but looking, I'm wondering why
>>>>> OvmfPkg/Library/QemuFwCfgLib doesn't have arm support, rather than
>>>>> putting it into a separate module over in
>>>>> ArmPlatformPkg/ArmVirtualizationPkg/Library/QemuFwCfgLib.
>>>>
>>>> (a) OvmfPkg/Library/QemuFwCfgLib shares the C-language implementation of
>>>> InternalQemuFwCfgReadBytes() between Ia32 and X64, and the underlying
>>>> IoReadFifo8() function has platform-dependent assembly implementation.
>>>> Whereas ArmPlatformPkg/ArmVirtualizationPkg/Library/QemuFwCfgLib has an
>>>> implementation that differs even on the C language level (and no
>>>> assembly at all).
>>>>
>>>> The library constructor is also different; the latter depends on
>>>> ARM-specific PCDs. It seemed cleaner to break away completely than to
>>>> litter the code with MDE_CPU_* macros, different INF sections, and mix
>>>> in some assembly too.
>>>
>>> I'm thinking arch specific C files, possibly only with
>>> InternalQemuFwCfgReadBytes. It does seem like a single implementation
>>> of QemuFwCfgLib is possible. Regarding the PCDs, I would say they
>>> could be fixed or dynamic depending on the platform. Anyway, I guess
>>> this is more of a cleanup issue at this point...
>>
>> The PCDs are only needed for the memory-mapped fw_cfg registers, and
>> they are detected / set from the DTB. x86 uses IO ports.
>>
>>> Regarding the other issue. How about instead of yet-another-library,
>>> we add OvmfPkg/AcpiPlatformDxe/QemuFwCfgAcpiDxe.inf that only supports
>>> fw-cfg?
>>
>> I assume that in that case, the following two files:
>> - OvmfPkg/AcpiPlatformDxe/AcpiPlatformDxe.inf (current)
>> - OvmfPkg/AcpiPlatformDxe/QemuFwCfgAcpiDxe.inf (suggested)
>>
>> would list different "AcpiPlatform.c" files (ie. the "outer shell" of
>> the drivers would differ), but both INF files would include Qemu.c from
>> that directory (and QemuFwCfgAcpiDxe would only utilize a part of
>> Qemu.obj). Then, ARM would include QemuFwCfgAcpiDxe.inf.
>>
>> I can only speak for myself, but I find several INF files per directory,
>> with an overlapping set of [Sources], *much* more confusing than a new
>> library (with appropriate dependencies). In fact this is my pet peeve with:
>> - OvmfPkg/Library/QemuFwCfgLib/
>> - ArmPlatformPkg/MemoryInitPei/
>> - ArmPlatformPkg/PlatformPei/
>> - MdeModulePkg/Library/SmmLockBoxLib/
>>
>> Whenever I have to look at these directories (and that's "frequently"),
>> my brain melts.
>>
>> ... What is your criticism against introducing QemuLoaderLib, summarily?
>
> To add this support to OvmfPkg/AcpiPlatformDxe, you'd need to add 1
> .inf and 1 .c file.
>
> To extract it out, you now have a new library (with a single function)
> that is used by two separate drivers.
>
> It is also conceivable that an OVMF build could use
> QemuFwCfgAcpiDxe.inf in some scenario where it only wanted to target
> newer QEMU builds.
Understood.
I'm not convinced, but I'll rework the series with QemuFwCfgAcpiDxe, my
conviction notwithstanding.
Thanks
Laszlo
> Regarding merging QemuFwCfgLib implementations, supporting multiple
> architectures in a single module is one thing that EDK II has put some
> effort into. It seems like a good candiate to me. But, that is a
> separate task anyhow.
>
> -Jordan
>
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