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ahci: give another shot at clearing all bits in irq_stat

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Commit ea0c62f7cf tried to clear all
bits in irq_stat but it didn't actually achieve that as irq_stat was
anded with port_map right after read.  This patch makes ahci driver
always use the unmasked value to clear irq_status.

While at it, add explanation on the peculiarities of ahci IRQ
clearing.

This was spotted by Linus Torvalds.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Tejun Heo 2008-07-05 13:10:50 +09:00 committed by Linus Torvalds
parent d79df630f6
commit d28f87aa87
1 changed files with 13 additions and 3 deletions
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16
drivers/ata/ahci.c
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@ -1777,7 +1777,7 @@ static irqreturn_t ahci_interrupt(int irq, void *dev_instance)
struct ahci_host_priv *hpriv;
unsigned int i, handled = 0;
void __iomem *mmio;
u32 irq_stat;
u32 irq_stat, irq_masked;
VPRINTK("ENTER\n");
@ -1786,16 +1786,17 @@ static irqreturn_t ahci_interrupt(int irq, void *dev_instance)
/* sigh. 0xffffffff is a valid return from h/w */
irq_stat = readl(mmio + HOST_IRQ_STAT);
irq_stat &= hpriv->port_map;
if (!irq_stat)
return IRQ_NONE;
irq_masked = irq_stat & hpriv->port_map;
spin_lock(&host->lock);
for (i = 0; i < host->n_ports; i++) {
struct ata_port *ap;
if (!(irq_stat & (1 << i)))
if (!(irq_masked & (1 << i)))
continue;
ap = host->ports[i];
@ -1812,6 +1813,15 @@ static irqreturn_t ahci_interrupt(int irq, void *dev_instance)
handled = 1;
}
/* HOST_IRQ_STAT behaves as level triggered latch meaning that
* it should be cleared after all the port events are cleared;
* otherwise, it will raise a spurious interrupt after each
* valid one. Please read section 10.6.2 of ahci 1.1 for more
* information.
*
* Also, use the unmasked value to clear interrupt as spurious
* pending event on a dummy port might cause screaming IRQ.
*/
writel(irq_stat, mmio + HOST_IRQ_STAT);
spin_unlock(&host->lock);