Commit ea0c62f7cf70f13a67830471b613337bd0c9a62e 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@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
---
The original report requires further investigation regarding why the
bogus change fixed the problem but this change is the correct thing to
do regardless.
Thanks.
drivers/ata/ahci.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
index 061817a..5e6468a 100644
--- a/drivers/ata/ahci.c
+++ b/drivers/ata/ahci.c
@@ -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);
--
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