ahci: give another shot at clearing all bits in irq_stat
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@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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 @@
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 @@
/* 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 @@
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);