Re: [PATCH v3 1/3] x86/amd_nb: Add support for northbridges on Aldebaran

On Mon, Sep 13, 2021 at 06:07:30PM +0000, Yazen Ghannam wrote:

I really like this idea. I've gone over the current and future code a few
times to make sure things are okay. As far as I can tell, this idea should
work most of the time, since the "node_id" value is mostly used to look up the
right devices in the nb array. But there is one case so far where the "real"
hardware node_id is needed during address translation.

Yap, I figured as much as this is kinda like the only place where you'd
care about the actual node id.

This case is in the new code in review for Data Fabric v3.5, and it
only applies to the GPU devices.

What do you think about having a couple of helper functions to go between the
hardware and Linux index IDs? Most cases will use "hardware -> Linux index",
and when needed there can be a "Linux index -> hardware".

That's fine as long as it is properly documented what it does.

I think we still need some piece of info to indicate a device is a GPU based
on its node_id. The AMD NB code doesn't need to know, but the address
translation code does. The AMD NB enumeration can be mostly generic. I think
it may be enough to save an "id offset" value and also a "first special index"
value. Then we can go back and forth between the appropriate values without
having to allocate a bunch of unused memory or hardcoding certain values.

Well, since we're going to need this in the translation logic and that
is part of amd64_edac and there we said we'll move the family type up
into amd64_pvt so that you can have a family descriptor per node, then I
guess you're all set. :-)

Thanks for the idea!

Sure, np.

Thx.

-- 
Regards/Gruss,
    Boris.

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