Re: [PATCH 06/13] sata_sil24: implement loss of completion interrupt on PCI-X errta fix

[Tejun Heo <htejun@gmail.com>]

Jeff Garzik wrote:
> Tejun Heo wrote:
>> @@ -738,6 +740,10 @@ static inline void sil24_host_intr(struc
>>      slot_stat = readl(port + PORT_SLOT_STAT);
>>      if (!(slot_stat & HOST_SSTAT_ATTN)) {
>>          struct sil24_port_priv *pp = ap->private_data;
>> +
>> +        if (ap->flags & SIL24_FLAG_PCIX_IRQ_WOC)
>> +            writel(PORT_IRQ_COMPLETE, port + PORT_IRQ_STAT);
>> +
> 
> 
> This looks racy.  Since the interrupt is usually level-triggered, 
> doesn't this introduce the possibility of losing interrupt events?
> 

Above code without the WOC flag test is actually equivalent to...

irq_stat = readl(port + PORT_IRQ_STAT);
if (irq_stat & 0xffff == PORT_IRQ_COMPLETE) {
	writel(PORT_IRQ_COMPLETE, port + PORT_IRQ_STAT);
	/* finish commands */
	return;
}
/* error processing */

So, no race condition that I can think of.  It's just like any other 
interrupt clearing.  Read it, clear it, handle it.  If anything happens 
before the clearing we catch it while handling (in this case, sil24 NCQ 
support will read outstanding command mask after clearing the 
interrupt).  if anything happens after the clearing, we'll be called again.

-- 
tejun