Re: [patch RFC 38/38] irqchip: Add IMS array driver - NOT FOR MERGING

[Thomas Gleixner]

On Sat, Aug 22 2020 at 20:05, Jason Gunthorpe wrote:
> On Sat, Aug 22, 2020 at 03:34:45AM +0200, Thomas Gleixner wrote:
> As a silicon design it might work, but it means existing devices can't
> be used with this dev_msi. It is also the sort of thing that would
> need a standard document to have any hope of multiple vendors fitting
> into it. Eg at PCI-SIG or something.

Fair enough.

>> If you don't do that then you simply can't write to that space from the
>> CPU and you have to transport this kind information always via command
>> queues.
>
> Yes, exactly. This is part of the architectural design of the device,
> has been for a long time. Has positives and negatives.

As always and it clearly follows the general HW design rule "we can fix
that in software".

>> > I suppose the core code could provide this as a service? Sort of a
>> > varient of the other lazy things above?
>> 
>> Kinda. That needs a lot of thought for the affinity setting stuff
>> because it can be called from contexts which do not allow that. It's
>> solvable though, but I clearly need to stare at the corner cases for a
>> while.
>
> If possible, this would be ideal, as we could use the dev_msi on a big
> installed base of existing HW.

I'll have a look, but I'm surely not going to like the outcome.

Thanks,

        tglx