[libata] PCI IDE command-end/irq-acknowledge cleanup

Restruct default irq handler (used for many PCI IDE-like SATA
controllers) to obtain device status and acknowledge interrupts
a bit differently.

In an attempt to better attack the "ich5 screaming interrupt" problem,
acknowledge and clear the device's INTRQ by reading the Status register
_before_ ack'ing the controller's irq status.  This is a deviation
from how the Linux IDE driver acknowledges interrupts, but it may
be the best method, since the ICH5 appears to continue to assert
the interrupt bit in the BMDMA until the device INTRQ line is cleared.

Of course, SATA has no INTRQ line per se, so ICH5 essentially has
new interrupt behavior not seen before in the PCI IDE world, while
pretending that it's compatible with PCI IDE.  Sigh.

This change affects all SATA controllers (for which there are libata
drivers) except for sata_promise and sata_sx4.

drivers/scsi/libata-core.c

@@ -50,7 +50,6 @@ static unsigned int ata_busy_sleep (struct ata_port *ap,
 				    unsigned long tmout_pat,
 			    	    unsigned long tmout);
 static void __ata_dev_select (struct ata_port *ap, unsigned int device);
-static void ata_dma_complete(struct ata_queued_cmd *qc, u8 host_stat);
 static void ata_host_set_pio(struct ata_port *ap);
 static void ata_host_set_udma(struct ata_port *ap);
 static void ata_dev_set_pio(struct ata_port *ap, unsigned int device);
@@ -2136,7 +2135,7 @@ static void ata_pio_task(void *_data)
 
 void ata_eng_timeout(struct ata_port *ap)
 {
-	u8 host_stat, drv_stat;
+	u8 host_stat = 0, drv_stat;
 	struct ata_queued_cmd *qc;
 
 	DPRINTK("ENTER\n");
@@ -2157,30 +2156,28 @@ void ata_eng_timeout(struct ata_port *ap)
 	qc->scsidone = scsi_finish_command;
 
 	switch (qc->tf.protocol) {
+
 	case ATA_PROT_DMA:
+	case ATA_PROT_ATAPI_DMA:
 		host_stat = ata_bmdma_status(ap);
 
-		printk(KERN_ERR "ata%u: DMA timeout, stat 0x%x\n",
-		       ap->id, host_stat);
+		/* before we do anything else, clear DMA-Start bit */
+		ata_bmdma_stop(ap);
 
-		ata_dma_complete(qc, host_stat);
-		break;
+		/* fall through */
 
 	case ATA_PROT_NODATA:
-		drv_stat = ata_busy_wait(ap, ATA_BUSY | ATA_DRQ, 1000);
-
-		printk(KERN_ERR "ata%u: command 0x%x timeout, stat 0x%x\n",
-		       ap->id, qc->tf.command, drv_stat);
-
-		ata_qc_complete(qc, drv_stat);
-		break;
-
 	default:
-		drv_stat = ata_busy_wait(ap, ATA_BUSY | ATA_DRQ, 1000);
+		ata_altstatus(ap);
+		drv_stat = ata_chk_status(ap);
+
+		/* ack bmdma irq events */
+		ata_bmdma_ack_irq(ap);
 
-		printk(KERN_ERR "ata%u: unknown timeout, cmd 0x%x stat 0x%x\n",
-		       ap->id, qc->tf.command, drv_stat);
+		printk(KERN_ERR "ata%u: command 0x%x timeout, stat 0x%x host_stat 0x%x\n",
+		       ap->id, qc->tf.command, drv_stat, host_stat);
 
+		/* complete taskfile transaction */
 		ata_qc_complete(qc, drv_stat);
 		break;
 	}
@@ -2412,7 +2409,7 @@ void ata_bmdma_setup_mmio (struct ata_queued_cmd *qc)
 {
 	struct ata_port *ap = qc->ap;
 	unsigned int rw = (qc->tf.flags & ATA_TFLAG_WRITE);
-	u8 host_stat, dmactl;
+	u8 dmactl;
 	void *mmio = (void *) ap->ioaddr.bmdma_addr;
 
 	/* load PRD table addr. */
@@ -2426,10 +2423,6 @@ void ata_bmdma_setup_mmio (struct ata_queued_cmd *qc)
 		dmactl |= ATA_DMA_WR;
 	writeb(dmactl, mmio + ATA_DMA_CMD);
 
-	/* clear interrupt, error bits */
-	host_stat = readb(mmio + ATA_DMA_STATUS);
-	writeb(host_stat | ATA_DMA_INTR | ATA_DMA_ERR, mmio + ATA_DMA_STATUS);
-
 	/* issue r/w command */
 	ap->ops->exec_command(ap, &qc->tf);
 }
@@ -2477,7 +2470,7 @@ void ata_bmdma_setup_pio (struct ata_queued_cmd *qc)
 {
 	struct ata_port *ap = qc->ap;
 	unsigned int rw = (qc->tf.flags & ATA_TFLAG_WRITE);
-	u8 host_stat, dmactl;
+	u8 dmactl;
 
 	/* load PRD table addr. */
 	outl(ap->prd_dma, ap->ioaddr.bmdma_addr + ATA_DMA_TABLE_OFS);
@@ -2489,11 +2482,6 @@ void ata_bmdma_setup_pio (struct ata_queued_cmd *qc)
 		dmactl |= ATA_DMA_WR;
 	outb(dmactl, ap->ioaddr.bmdma_addr + ATA_DMA_CMD);
 
-	/* clear interrupt, error bits */
-	host_stat = inb(ap->ioaddr.bmdma_addr + ATA_DMA_STATUS);
-	outb(host_stat | ATA_DMA_INTR | ATA_DMA_ERR,
-	     ap->ioaddr.bmdma_addr + ATA_DMA_STATUS);
-
 	/* issue r/w command */
 	ap->ops->exec_command(ap, &qc->tf);
 }
@@ -2517,29 +2505,6 @@ void ata_bmdma_start_pio (struct ata_queued_cmd *qc)
 	     ap->ioaddr.bmdma_addr + ATA_DMA_CMD);
 }
 
-/**
- *	ata_dma_complete - Complete an active ATA BMDMA command
- *	@qc: Command to complete
- *	@host_stat: BMDMA status register contents
- *
- *	LOCKING:
- */
-
-static void ata_dma_complete(struct ata_queued_cmd *qc, u8 host_stat)
-{
-	struct ata_port *ap = qc->ap;
-	VPRINTK("ENTER\n");
-
-	ata_bmdma_stop(ap);
-	ata_bmdma_ack_irq(ap);
-
-	DPRINTK("host %u, host_stat==0x%X, drv_stat==0x%X\n",
-		ap->id, (u32) host_stat, (u32) ata_chk_status(ap));
-
-	/* get drive status; clear intr; complete txn */
-	ata_qc_complete(qc, ata_wait_idle(ap));
-}
-
 /**
  *	ata_host_intr - Handle host interrupt for given (port, task)
  *	@ap: Port on which interrupt arrived (possibly...)
@@ -2560,55 +2525,60 @@ inline unsigned int ata_host_intr (struct ata_port *ap,
 				   struct ata_queued_cmd *qc)
 {
 	u8 status, host_stat;
-	unsigned int handled = 0;
 
 	switch (qc->tf.protocol) {
 
-	/* BMDMA completion */
 	case ATA_PROT_DMA:
 	case ATA_PROT_ATAPI_DMA:
+		/* check status of DMA engine */
 		host_stat = ata_bmdma_status(ap);
 		VPRINTK("BUS_DMA (host_stat 0x%X)\n", host_stat);
 
-		if (!(host_stat & ATA_DMA_INTR)) {
-			ap->stats.idle_irq++;
-			break;
-		}
+		/* if it's not our irq... */
+		if (!(host_stat & ATA_DMA_INTR))
+			goto idle_irq;
 
-		ata_dma_complete(qc, host_stat);
-		handled = 1;
-		break;
+		/* before we do anything else, clear DMA-Start bit */
+		ata_bmdma_stop(ap);
+
+		/* fall through */
 
-	/* command completion, but no data xfer */
-	/* FIXME: a shared interrupt _will_ cause a non-data command
-	 * to be completed prematurely, with an error.
-	 *
-	 * This doesn't matter right now, since we aren't sending
-	 * non-data commands down this pipe except in development
-	 * situations.
-	 */
-	case ATA_PROT_ATAPI:
 	case ATA_PROT_NODATA:
-		status = ata_busy_wait(ap, ATA_BUSY | ATA_DRQ, 1000);
-		DPRINTK("BUS_NODATA (drv_stat 0x%X)\n", status);
+		/* check altstatus */
+		status = ata_altstatus(ap);
+		if (status & ATA_BUSY)
+			goto idle_irq;
+
+		/* check main status, clearing INTRQ */
+		status = ata_chk_status(ap);
+		if (unlikely(status & ATA_BUSY))
+			goto idle_irq;
+		DPRINTK("BUS_NODATA (dev_stat 0x%X)\n", status);
+
+		/* ack bmdma irq events */
+		ata_bmdma_ack_irq(ap);
+
+		/* complete taskfile transaction */
 		ata_qc_complete(qc, status);
-		handled = 1;
 		break;
 
 	default:
-		ap->stats.idle_irq++;
+		goto idle_irq;
+	}
+
+	return 1;	/* irq handled */
+
+idle_irq:
+	ap->stats.idle_irq++;
 
 #ifdef ATA_IRQ_TRAP
-		if ((ap->stats.idle_irq % 1000) == 0) {
-			handled = 1;
-			ata_irq_ack(ap, 0); /* debug trap */
-			printk(KERN_WARNING "ata%d: irq trap\n", ap->id);
-		}
-#endif
-		break;
+	if ((ap->stats.idle_irq % 1000) == 0) {
+		handled = 1;
+		ata_irq_ack(ap, 0); /* debug trap */
+		printk(KERN_WARNING "ata%d: irq trap\n", ap->id);
 	}
-
-	return handled;
+#endif
+	return 0;	/* irq not handled */
 }
 
 /**
@@ -2642,7 +2612,7 @@ irqreturn_t ata_interrupt (int irq, void *dev_instance, struct pt_regs *regs)
 
 			qc = ata_qc_from_tag(ap, ap->active_tag);
 			if (qc && (!(qc->tf.ctl & ATA_NIEN)))
-				handled += ata_host_intr(ap, qc);
+				handled |= ata_host_intr(ap, qc);
 		}
 	}
 
@@ -2907,6 +2877,10 @@ int ata_device_add(struct ata_probe_ent *ent)
 		return 0;
 	}
 
+	/* TODO: ack irq here, to ensure it won't scream
+	 * when we enable it?
+	 */
+
 	/* obtain irq, that is shared between channels */
 	if (request_irq(ent->irq, ent->port_ops->irq_handler, ent->irq_flags,
 			DRV_NAME, host_set))