Re: [PATCH 11/12] libata: use IRQ expecting

From: Jeff Garzik
Date: Fri Jun 25 2010 - 05:48:14 EST

On 06/25/2010 03:44 AM, Tejun Heo wrote:
Hello, Jeff.

On 06/25/2010 02:22 AM, Jeff Garzik wrote:
@@ -4972,6 +4972,8 @@ void ata_qc_complete(struct ata_queued_cmd *qc)
struct ata_port *ap = qc->ap;

+ unexpect_irq(ap->irq_expect, false);
/* XXX: New EH and old EH use different mechanisms to
* synchronize EH with regular execution path.

Unconditional use of unexpect_irq() here seems incorrect for some cases,
such as sata_mv's use, where ata_qc_complete() is called multiple times
rather than a singleton ata_qc_complete_multiple() call.

Indeed, sata_mv is calling ata_qc_complete() directly multiple times.
I still think calling unexpect_irq() from ata_qc_complete() is correct
as ata_qc_complete() is always a good indicator of completion events.

My basic point is that you are implicitly changing the entire ata_qc_complete() API, and associated underlying assumptions.

The existing assumption, since libata day #0, is that ata_qc_complete() works entirely within the scope of a single qc -- thus enabling multiple calls for a single controller interrupt. Your change greatly widens the scope to an entire port.

This isn't just an issue with sata_mv, that was just the easy example I remember off the top of my head. sata_fsl and sata_nv also make the same assumption. And it's a reasonable assumption, IMO.

I think an unexpect_irq() call is more appropriate outside ata_qc_complete().


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