linux-kernel - Re: [PATCH v5 4/5] Driver core: platform: Add devm_platform_get_irqs

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Date:   Wed, 9 Dec 2020 20:13:15 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     John Garry <john.garry@...wei.com>
Cc:     jejb@...ux.ibm.com, martin.petersen@...cle.com, lenb@...nel.org,
        rjw@...ysocki.net, tglx@...utronix.de, maz@...nel.org,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxarm@...wei.com, linux-acpi@...r.kernel.org, dwagner@...e.de
Subject: Re: [PATCH v5 4/5] Driver core: platform: Add
 devm_platform_get_irqs_affinity()

On Wed, Dec 09, 2020 at 07:04:02PM +0000, John Garry wrote:
> On 09/12/2020 18:32, Greg KH wrote:
> > On Wed, Dec 02, 2020 at 06:36:56PM +0800, John Garry wrote:
> > > Drivers for multi-queue platform devices may also want managed interrupts
> > > for handling HW queue completion interrupts, so add support.
> > 
> 
> Hi Greg,
> 
> > Why would a platform device want all of this?  Shouldn't such a device
> > be on a "real" bus instead?
> 
> For this HW version, the device is on the system bus, directly addressable
> by the CPU.

What do you mean by "system bus"?

> 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 series https://lore.kernel.org/linux-scsi/1606905417-183214-1-git-send-email-john.garry@huawei.com/T/#m0df7e7cd6f0819b99aaeb6b7f8939ef1e17b8a83.

Ah, I missed that, I thought that was some high-speed scsi thing, not a
tiny platform driver...

> 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.

thanks,

greg k-h