Re: [edk2-devel] [PATCH v2 3/7] OvmfPkg: Add the QemuFwCfgMmioLib PEI stage version

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

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Hi Gerd,

I get it, I will refactor the code as soon as I can, it looks like 
there's still some work and will take some time. I will try to send the 
V3 tonight if possible.


Thanks,
Chao
On 2024/4/25 17:02, Gerd Hoffmann wrote:
> On Thu, Apr 25, 2024 at 04:06:13PM +0800, Chao Li wrote:
>> Hi Gerd,
>>
>>
>> Thanks,
>> Chao
>> On 2024/4/25 15:53, Gerd Hoffmann wrote:
>>>     Hi,
>>>
>>>> +UINTN  mFwCfgSelectorAddress;
>>>> +UINTN  mFwCfgDataAddress;
>>>> +UINTN  mFwCfgDmaAddress;
>>> Hmm, global variables for PEI?  I think the point of storing these in
>>> the HOB is to avoid the need for global variables?  Also does that work
>>> when running PEI in-place from flash?
>> I think it would be useful if some platforms(not LoongArch) could use the
>> global variables in PEI, because the global variables are faster.
> Performance isn't my main concern here, I very much prefer code which is
> easy to maintain.  Taking the same code path on all platforms is good
> for that.  It's less code and it also makes testing easier.  The risk of
> breaking loongarch when changing something for riscv or arm is much
> lower if all platforms work the same way.
>
> I'd suggest to first refactor the existing DXE code to use a HOB instead
> of global variables.  Have a helper function which looks up the HOB and
> returns a pointer to the configuration struct.  That helper function can
> be slightly different for DXE/PEI, the DXE variant can cache the pointer
> to the struct in a global variable so it needs to do the lookup only
> once.
>
>>>> +  UINT64        FwCfgDataSize;
>>>> +  UINT64        FwCfgDmaAddress;
>>>> +  UINT64        FwCfgDmaSize;
>>> First thing this function should do is check whenever the HOB already
>>> exists.  Should that be the case there is no need to parse the device
>>> tree.
>> This is a constructor in PEI, that has to parse the device tree and then
>> build the HOBs.
> This is a library, so it can be linked into multiple PEI and DXE
> modules.  So it must be prepared to run multiple times.  On the
> second and all following runs the HOB will already exist.
>
> The DXE variant will need the check for sure.  I'd strongly suggest to
> add it to the PEI variant too, even though it might not be needed right
> now because PlatformPei is the only PEI module using the library.
>
> take care,
>    Gerd
>
>
>
> 
>


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