[SCSI] hpsa: allow driver to put controller in either simple or performant mode

Signed-off-by: Stephen M. Cameron <scameron@beardog.cce.hp.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>

Documentation/scsi/hpsa.txt

@@ -28,6 +28,12 @@ boot parameter "hpsa_allow_any=1" is specified, however these are not tested
 nor supported by HP with this driver.  For older Smart Arrays, the cciss
 driver should still be used.
 
+The "hpsa_simple_mode=1" boot parameter may be used to prevent the driver from
+putting the controller into "performant" mode.  The difference is that with simple
+mode, each command completion requires an interrupt, while with "performant mode"
+(the default, and ordinarily better performing) it is possible to have multiple
+command completions indicated by a single interrupt.
+
 HPSA specific entries in /sys
 -----------------------------
 

drivers/scsi/hpsa.c

@@ -74,6 +74,10 @@ static int hpsa_allow_any;
 module_param(hpsa_allow_any, int, S_IRUGO|S_IWUSR);
 MODULE_PARM_DESC(hpsa_allow_any,
 		"Allow hpsa driver to access unknown HP Smart Array hardware");
+static int hpsa_simple_mode;
+module_param(hpsa_simple_mode, int, S_IRUGO|S_IWUSR);
+MODULE_PARM_DESC(hpsa_simple_mode,
+	"Use 'simple mode' rather than 'performant mode'");
 
 /* define the PCI info for the cards we can control */
 static const struct pci_device_id hpsa_pci_device_id[] = {
@@ -4038,6 +4042,9 @@ static __devinit void hpsa_put_ctlr_into_performant_mode(struct ctlr_info *h)
 {
 	u32 trans_support;
 
+	if (hpsa_simple_mode)
+		return;
+
 	trans_support = readl(&(h->cfgtable->TransportSupport));
 	if (!(trans_support & PERFORMANT_MODE))
 		return;