Re: [PATCH V4 1/3] driver core: mark device as irq affinity managed if any irq is managed

[John Garry <john.garry@huawei.com>]

On 19/07/2021 10:44, Christoph Hellwig wrote:
> On Mon, Jul 19, 2021 at 08:51:22AM +0100, John Garry wrote:
>>> Address this issue by adding one field of .irq_affinity_managed into
>>> 'struct device'.
>>>
>>> Suggested-by: Christoph Hellwig <hch@lst.de>
>>> Signed-off-by: Ming Lei <ming.lei@redhat.com>
>>
>> Did you consider that for PCI device we effectively have this info already:
>>
>> bool dev_has_managed_msi_irq(struct device *dev)
>> {
>> 	struct msi_desc *desc;
>>
>> 	list_for_each_entry(desc, dev_to_msi_list(dev), list)

I just noticed for_each_msi_entry(), which is the same


>> 		if (desc->affinity && desc->affinity->is_managed)
>> 			return true;
>> 	}
>>
>> 	return false;
> 
> Just walking the list seems fine to me given that this is not a
> performance criticial path.  But what are the locking implications?

Since it would be used for sequential setup code, I didn't think any 
locking was required. But would need to consider where that function 
lived and whether it's public.

> 
> Also does the above imply this won't work for your platform MSI case?
> .
> 

Right. I think that it may be possible to reach into the platform msi 
descriptors to get this info, but I am not sure it's worth it. There is 
only 1x user there and there is no generic .map_queues function, so 
could set the flag directly:

int blk_mq_pci_map_queues(struct blk_mq_queue_map *qmap, struct pci_dev 
*pdev,
  		for_each_cpu(cpu, mask)
  			qmap->mq_map[cpu] = qmap->queue_offset + queue;
  	}
+	qmap->use_managed_irq = dev_has_managed_msi_irq(&pdev->dev);
}

--- a/drivers/scsi/hisi_sas/hisi_sas_v2_hw.c
+++ b/drivers/scsi/hisi_sas/hisi_sas_v2_hw.c
@@ -3563,6 +3563,8 @@ static int map_queues_v2_hw(struct Scsi_Host *shost)
                        qmap->mq_map[cpu] = qmap->queue_offset + queue;
        }

+       qmap->use_managed_irq = 1;
+
        return 0;
}