Re: [PATCH v3 1/8] driver core: bus: add irq_get_affinity callback to bus_type

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, Nov 13, 2024 at 01:44:02PM +0000, John Garry wrote:
> On 13/11/2024 12:36, Daniel Wagner wrote:
> > > > @@ -48,6 +48,7 @@ struct fwnode_handle;
> > > >     *		will never get called until they do.
> > > >     * @remove:	Called when a device removed from this bus.
> > > My impression is that this would be better suited to "struct device_driver",
> > > but I assume that there is a good reason to add to "struct bus_type".
> > I think the main reason to put it here is that most of the drivers are
> > happy with the getter on bus level and don't need special treatment. We
> > don't have to touch all the drivers to hookup a common getter, nor do we
> > have to install a default handler when the driver doesn't specify one.
> > Having the callback in struct bus_driver avoids this. Though Christoph
> > suggested it, so I can only guess.
> > 
> > But you bring up a good point, if we had also an irq_get_affinity
> > callback in struct device_driver it would be possible for the
> > hisi_sas v2 driver to provide a getter and blk_mq_hctx_map_queues could
> > do:
> > 
> > 	for (queue = 0; queue < qmap->nr_queues; queue++) {
> > 		if (dev->driver->irq_get_affinity)
> > 			mask = dev->driver->irq_get_affinity;
> > 		else if (dev->bus->irq_get_affinity)
> > 			mask = dev->bus->irq_get_affinity(dev, queue + offset);
> > 		if (!mask)
> > 			goto fallback;
> > 
> > 		for_each_cpu(cpu, mask)
> > 			qmap->mq_map[cpu] = qmap->queue_offset + queue;
> > 	}
> > 
> > and with this in place the open coded version in hisi_sas v2 can also be
> > replaced.
> 
> Yeah, I think that it could be plugged in like:
> 
> diff --git a/drivers/scsi/hisi_sas/hisi_sas_v2_hw.c
> b/drivers/scsi/hisi_sas/hisi_sas_v2_hw.c
> index 342d75f12051..5172af77a3f0 100644
> --- a/drivers/scsi/hisi_sas/hisi_sas_v2_hw.c
> +++ b/drivers/scsi/hisi_sas/hisi_sas_v2_hw.c
> @@ -3636,6 +3636,7 @@ static struct platform_driver hisi_sas_v2_driver = {
>                .name = DRV_NAME,
>                .of_match_table = sas_v2_of_match,
>                .acpi_match_table = ACPI_PTR(sas_v2_acpi_match),
> +               .irq_get_affinity_mask = hisi_sas_v2_get_affinity_mask,
>        },
> };
> 
> 
> > If no one objects, I go ahead and add the callback to struct
> > device_driver.
> 
> I'd wait for Christoph and Greg to both agree. I was just wondering why we
> use bus_type.

bus types are good to set it at a bus level so you don't have to
explicitly set it at each-and-every-driver.  Depends on what you want
this to be, if it is a "all drivers of this bus type will have the same
callback" then put it on the bus.  otherwise if you are going to
mix/match on a same bus, then put it in the driver structure.

hope this helps,

greg k-h