[PATCH] libata: waits up to 10 microseconds for early irq problem

[Albert Lee <albertcc@tw.ibm.com>]

Some devices raise irq early before clearing the BSY.
This patch waits up to 10 microseconds to workaround the early irq problem.

Signed-off-by: Albert Lee <albertcc@tw.ibm.com>
---
In additional to the pata_via SET FEATURES XFER problem reported by Matthieu,
we also see the early irq problem with ICH4 + AOpen CD-936E on READ under PIO mode 4.

The following is a port of the pata_via_fix to the libata core.
Patch against 2.6.19-rc6. For your review, thanks.


--- linux-2.6.19-rc6/include/linux/libata.h	2006-11-28 11:14:52.000000000 +0800
+++ linux-2.6.19-rc6-early_irq/include/linux/libata.h	2006-11-28 13:31:07.565194648 +0800
@@ -1039,6 +1039,30 @@ static inline void ata_pause(struct ata_
 	ndelay(400);
 }
 
+/**
+ *	ata_busy_wait_alt - Wait for a port alt status register
+ *	@ap: Port to wait for.
+ *
+ *	Waits up to max microseconds for the selected bits in the port's
+ *	alt status register to be cleared.
+ *	Returns final value of alt status register.
+ *
+ *	LOCKING:
+ *	Inherited from caller.
+ */
+static inline u8 ata_busy_wait_alt(struct ata_port *ap, unsigned int bits,
+				   unsigned int max)
+{
+	u8 status = ata_altstatus(ap);
+
+	while ((status & bits) && (max > 0)) {
+		udelay(1);
+		status = ata_altstatus(ap);
+		max--;
+	};
+
+	return status;
+}
 
 /**
  *	ata_busy_wait - Wait for a port status register
--- linux-2.6.19-rc6/drivers/ata/libata-core.c	2006-11-28 11:14:38.000000000 +0800
+++ linux-2.6.19-rc6-early_irq/drivers/ata/libata-core.c	2006-11-28 13:31:31.275590120 +0800
@@ -4828,8 +4828,10 @@ inline unsigned int ata_host_intr (struc
 		goto idle_irq;
 	}
 
-	/* check altstatus */
-	status = ata_altstatus(ap);
+	/* check altstatus.
+	 * Waits up to 10 microseconds for early irq.
+	 */
+	status = ata_busy_wait_alt(ap, ATA_BUSY, 10);
 	if (status & ATA_BUSY)
 		goto idle_irq;