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

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Message-ID: <bed15207-c3d8-4e0b-b356-4880f5a4fdff@oracle.com>
Date: Wed, 13 Nov 2024 13:44:02 +0000
From: John Garry <john.g.garry@...cle.com>
To: Daniel Wagner <dwagner@...e.de>
Cc: Daniel Wagner <wagi@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        Eugenio Pérez <eperezma@...hat.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Keith Busch <kbusch@...nel.org>, Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, virtualization@...ts.linux.dev,
        linux-scsi@...r.kernel.org, megaraidlinux.pdl@...adcom.com,
        mpi3mr-linuxdrv.pdl@...adcom.com, MPT-FusionLinux.pdl@...adcom.com,
        storagedev@...rochip.com, linux-nvme@...ts.infradead.org
Subject: Re: [PATCH v3 1/8] driver core: bus: add irq_get_affinity callback to
 bus_type

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.