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.

---
I just had another run with pata_ali. I tried various things w/o any success. I just can't see what's the difference between alim15x3 and pata_ali. I again tried to make the command issue path of pata_ali + libata behave virtually identical to alim15x3 but it just didn't work. :-( :-( :-(

drivers/ata/pata_ali.c | 40 ++++++++++++++++++++++++++++++++++++++++

1 file changed, 40 insertions(+)

index 8786455..ce830fe 100644
@@ -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
*/
@@ -270,6 +274,27 @@ 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
+ * [email protected] and cc [email protected].
+ *
+ * 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,

applied