Re: [PATCH 0/5] serial: Add MMIO & SPCR support for AWS EC2 metal instances

[Benjamin Herrenschmidt]

On Thu, 2021-03-18 at 19:03 -0500, Glenn Washburn wrote:
> > This was tested using SPCR on an actual c5.metal instance, and using
> > explicit instanciation via serial -p mmioXXXXXXXX on a modified qemu
> > hacked to create MMIO PCI serial ports.
> 
> 
> When you say a modified qemu, was that a source level change? I'm
> curious how hard it would be to add this test to the current GRUB make
> check tests (many of which already use qemu). Of course, if they source
> of qemu was modified, then its probably a deal breaker (until it could
> be accepted upstream). 

Yes, I added an "mmio" option to pci-serial that makes register with
the Amazon UART vid/did and use an MMIO BAR :-) It's a bit of a hack
but I can try upstreaming it.

> Also I haven't looked into it, but seems like it might not be hard to
> add a separate test for the part using the SPCR table via qemu (perhaps
> using the "-acpitable" arg).

My experience with ACPI is extremely limited, I've never done such
things as build tables etc... but I can certainly try to look into it
as time permits.

> Also, could you add to the documentation on the usage of these changes?

I added some documentation to the "serial" command syntax change for
MMIO. I didn't add anything about SPCR indeed, where do you suggest I
add it ? Same spot ?

> New functionality should in general come with new tests (when feasible)

Yes, I understand, it's just that in this specific case it's rather
hard ... :-) I'll see what I can do with qemu but the best case
scenario would involve upstreaming something there and then depending
on that change trickling down to be able to use it in the grub tests
which would be ... tricky....

> and additions to the documentation.

Right, I did a bit, I can look into adding more, let me know if there
are other parts of the doc you wish me to update.

Cheers,
Ben.