pata_ali: disable ATAPI DMA

ATAPI DMA just doesn't work reliably on pata_ali.  The IDE driver can
do it but for some mysterious reason, pata_ali can't.  This patch
disables it by default and makes the driver whine during
initialization.  "pata_ali.atapi_dma" parameter is added so that user
can bypass the workaround.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/ata/pata_ali.c

@@ -36,6 +36,10 @@
 #define DRV_NAME "pata_ali"
 #define DRV_VERSION "0.7.5"
 
+int ali_atapi_dma = 0;
+module_param_named(atapi_dma, ali_atapi_dma, int, 0644);
+MODULE_PARM_DESC(atapi_dma, "Enable ATAPI DMA (0=disable, 1=enable)");
+
 /*
  *	Cable special cases
  */
@@ -269,6 +273,27 @@ static void ali_set_dmamode(struct ata_port *ap, struct ata_device *adev)
 	}
 }
 
+/**
+ *	ali_warn_atapi_dma	-	Warn about ATAPI DMA disablement
+ *	@adev: Device
+ *
+ *	Whine about ATAPI DMA disablement if @adev is an ATAPI device.
+ *	Can be used as ->dev_config.
+ */
+
+static void ali_warn_atapi_dma(struct ata_device *adev)
+{
+	struct ata_eh_context *ehc = &adev->link->eh_context;
+	int print_info = ehc->i.flags & ATA_EHI_PRINTINFO;
+
+	if (print_info && adev->class == ATA_DEV_ATAPI && !ali_atapi_dma) {
+		ata_dev_printk(adev, KERN_WARNING,
+			       "WARNING: ATAPI DMA disabled for reliablity issues.  It can be enabled\n");
+		ata_dev_printk(adev, KERN_WARNING,
+			       "WARNING: via pata_ali.atapi_dma modparam or corresponding sysfs node.\n");
+	}
+}
+
 /**
  *	ali_lock_sectors	-	Keep older devices to 255 sector mode
  *	@adev: Device
@@ -283,6 +308,7 @@ static void ali_set_dmamode(struct ata_port *ap, struct ata_device *adev)
 static void ali_lock_sectors(struct ata_device *adev)
 {
 	adev->max_sectors = 255;
+	ali_warn_atapi_dma(adev);
 }
 
 /**
@@ -294,6 +320,18 @@ static void ali_lock_sectors(struct ata_device *adev)
 
 static int ali_check_atapi_dma(struct ata_queued_cmd *qc)
 {
+	if (!ali_atapi_dma) {
+		/* FIXME: pata_ali can't do ATAPI DMA reliably but the
+		 * IDE alim15x3 driver can.  I tried lots of things
+		 * but couldn't find what the actual difference was.
+		 * If you got an idea, please write it to
+		 * linux-ide@vger.kernel.org and cc htejun@gmail.com.
+		 *
+		 * Disable ATAPI DMA for now.
+		 */
+		return -EOPNOTSUPP;
+	}
+
 	/* If its not a media command, its not worth it */
 	if (atapi_cmd_type(qc->cdb[0]) == ATAPI_MISC)
 		return -EOPNOTSUPP;
@@ -359,6 +397,7 @@ static struct ata_port_operations ali_20_port_ops = {
 
 	.tf_load	= ata_tf_load,
 	.tf_read	= ata_tf_read,
+	.check_atapi_dma = ali_check_atapi_dma,
 	.check_status 	= ata_check_status,
 	.exec_command	= ata_exec_command,
 	.dev_select 	= ata_std_dev_select,
@@ -438,6 +477,7 @@ static struct ata_port_operations ali_c5_port_ops = {
 	.check_status 	= ata_check_status,
 	.exec_command	= ata_exec_command,
 	.dev_select 	= ata_std_dev_select,
+	.dev_config	= ali_warn_atapi_dma,
 
 	.freeze		= ata_bmdma_freeze,
 	.thaw		= ata_bmdma_thaw,