Re: [PATCH v5 4/5] Driver core: platform: Add devm_platform_get_irqs_affinity()

[John Garry]

On 09/12/2020 19:13, Greg KH wrote:

Hi Greg,

> > For this HW version, the device is on the system bus, directly addressable
> > by the CPU.
> What do you mean by "system bus"?

Maybe my terminology is wrong, the point is that we have a platform 
device driver.

> > Motivation is that I wanted to switch the HW completion queues to use
> > managed interrupts.
> Fair enough, seems like overkill for a "platform" bus though:)
>
> > > What in-kernel driver needs this complexity?  I can't take new apis
> > > without a real user in the tree, sorry.
> > It's in the final patch in the serieshttps://lore.kernel.org/linux-scsi/1606905417-183214-1-git-send-email-john.garry@xxxxxxxxxx/T/#m0df7e7cd6f0819b99aaeb6b7f8939ef1e17b8a83.
> Ah, I missed that, I thought that was some high-speed scsi thing, not a
> tiny platform driver...

It is actually is a high-speed SCSI thing also, SAS 3.0 :)

> > I don't anticipate a huge number of users of this API in future, as most
> > multi-queue devices are PCI devices; so we could do the work of this API in
> > the driver itself, but the preference was not to export genirq functions
> > like irq_update_affinity_desc() or irq_create_affinity_masks(), and rather
> > have a common helper in the core platform code.
> Ok, I'd like to have the irq maintainers/developers ack this before
> taking it in the driver core, as someone is going to have to maintain
> this crazy thing for forever if it gets merged.

irq experts are cc'ed and have been very helpful here

So the API mushroomed a bit over time, as I realized that we need to 
support tearing down the irq mapping, make as devm method, use 
irq_calc_affinity_vectors(). Not sure how we could factor any of it out 
to become less of your problem.

Thanks,
John