Re: [edk2-devel] [edk2-platforms][PATCH V1 07/11] Platform/ARM/Morello: Port PCI Express library

["chandni cherukuri" <ch.chandni@gmail.com>]

Hi Ard, Leif, Sami, Pierre,

For Morello platform, we created two custom libraries based on the
below two native libraries:
-          https://github.com/tianocore/edk2/tree/master/MdePkg/Library/BasePciSegmentLibPci
-          https://github.com/tianocore/edk2/tree/master/MdePkg/Library/BasePciExpressLib

because of the following reasons.
1.       In Morello platform, the ECAM region of the two root ports
are placed in non-contiguous memory as per the memory map architecture
of the Morello platform. The native PCI Express Library expects both
the ECAM regions for all the root ports to be contiguous.
2.       IORT and kernel currently require each root port to be in a
separate segment. You can refer to the code for more details -
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/acpi/arm64/iort.c#n307.
The native PCI Segment Library supports only a single segment.

Because of these reasons, the current patch series adapts the native
libraries as follows:

The custom PCI Segment Library passes the complete address which is
consumed by the custom PCI Express library where based on the Segment
number, the base address of the PCI Express is returned.

The rationale behind maintaining two separate libraries is that when
the software evolves and support for multiple segments is adapted in
the native PCI Segment Library the custom library could be removed.
Also, we might have other protocols which might try to use the PCI
Express library directly. However, there are some other platforms
where all the platform specific changes have gone in a single custom
PCI library

Could you please provide some inputs as to which of two approaches
would be better to follow as there is one more platform to follow
based on the decision taken?

Thanks
Chandni

On Wed, Dec 8, 2021 at 8:25 AM Khasim Mohammed <khasim.mohammed@arm.com> wrote:
>
> Hi Sami, Chandni,
>
> There was a suggestion from Pierre on a similar patch for N1SDP to remove PCIExpressLib.c and move to workarounds to PCISegmentLib.c,
>
> https://edk2.groups.io/g/devel/message/84165?p=%2C%2C%2C20%2C0%2C0%2C0%3A%3Arecentpostdate%2Fsticky%2C%2Ckhasim%2C20%2C2%2C0%2C87257273
>
> I think we should discuss this implementation for both N1SDP and Morello as they have similar implementation.
>
> Regards,
> Khasim
>