scsi: ppa: Add a module parameter for the transfer mode

I have an Iomega Z100P2 zip drive, but it does not work with my StarTech
PEX1P2 AX99100 PCIe parallel port, which evidently does not support 16-bit
or 32-bit EPP. Currently the only way to tell the PPA driver to use 8-bit
EPP is to write 'mode=3' to /proc/scsi/ppa/*, but the driver doesn't
actually distinguish between the three EPP modes and still tries to use
16-bit or 32-bit EPP. And even if writing to that file did make the driver
use 8-bit EPP, it still wouldn't do me any good because by the time that
file exists, the drive has already failed to initialize.

Add a new parameter /sys/module/ppa/mode to set the transfer mode before
initializing the drive. This parameter replaces the use of
CONFIG_SCSI_IZIP_EPP16 in the PPA driver.

At the same time, default to 8-bit EPP. 16-bit and 32-bit EPP are not
necessary for the drive to function, nor are they part of the IEEE 1284
standard, so the driver should not assume that they are available.

Signed-off-by: Alex Henrie <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/Kconfig

···
 
 config SCSI_IZIP_EPP16
 	bool "ppa/imm option - Use slow (but safe) EPP-16"
-	depends on SCSI_PPA || SCSI_IMM
+	depends on SCSI_IMM
 	help
 	  EPP (Enhanced Parallel Port) is a standard for parallel ports which
 	  allows them to act as expansion buses that can handle up to 64

drivers/scsi/ppa.c

···
 
 #include  "ppa.h"
 
+static unsigned int mode = PPA_AUTODETECT;
+module_param(mode, uint, 0644);
+MODULE_PARM_DESC(mode, "Transfer mode (0 = Autodetect, 1 = SPP 4-bit, "
+	"2 = SPP 8-bit, 3 = EPP 8-bit, 4 = EPP 16-bit, 5 = EPP 32-bit");
+
 static struct scsi_pointer *ppa_scsi_pointer(struct scsi_cmnd *cmd)
 {
 	return scsi_cmd_priv(cmd);
···
 	return 0;
 }
 
-static int device_check(ppa_struct *dev);
+static int device_check(ppa_struct *dev, bool autodetect);
 
 #if PPA_DEBUG > 0
 #define ppa_fail(x,y) printk("ppa: ppa_fail(%i) from %s at line %d\n",\
···
 	case PPA_EPP_8:
 		epp_reset(ppb);
 		w_ctr(ppb, 0x4);
-#ifdef CONFIG_SCSI_IZIP_EPP16
-		if (!(((long) buffer | len) & 0x01))
-			outsw(ppb + 4, buffer, len >> 1);
-#else
-		if (!(((long) buffer | len) & 0x03))
+		if (dev->mode == PPA_EPP_32 && !(((long) buffer | len) & 0x01))
 			outsl(ppb + 4, buffer, len >> 2);
-#endif
+		else if (dev->mode == PPA_EPP_16 && !(((long) buffer | len) & 0x03))
+			outsw(ppb + 4, buffer, len >> 1);
 		else
 			outsb(ppb + 4, buffer, len);
 		w_ctr(ppb, 0xc);
···
 	case PPA_EPP_8:
 		epp_reset(ppb);
 		w_ctr(ppb, 0x24);
-#ifdef CONFIG_SCSI_IZIP_EPP16
-		if (!(((long) buffer | len) & 0x01))
-			insw(ppb + 4, buffer, len >> 1);
-#else
-		if (!(((long) buffer | len) & 0x03))
+		if (dev->mode == PPA_EPP_32 && !(((long) buffer | len) & 0x03))
 			insl(ppb + 4, buffer, len >> 2);
-#endif
+		else if (dev->mode == PPA_EPP_16 && !(((long) buffer | len) & 0x01))
+			insw(ppb + 4, buffer, len >> 1);
 		else
 			insb(ppb + 4, buffer, len);
 		w_ctr(ppb, 0x2c);
···
 {
 	int retv;
 	unsigned short ppb = dev->base;
+	bool autodetect = dev->mode == PPA_AUTODETECT;
+
+	if (autodetect) {
+		int modes = dev->dev->port->modes;
+		int ppb_hi = dev->dev->port->base_hi;
+
+		/* Mode detection works up the chain of speed
+		 * This avoids a nasty if-then-else-if-... tree
+		 */
+		dev->mode = PPA_NIBBLE;
+
+		if (modes & PARPORT_MODE_TRISTATE)
+			dev->mode = PPA_PS2;
+
+		if (modes & PARPORT_MODE_ECP) {
+			w_ecr(ppb_hi, 0x20);
+			dev->mode = PPA_PS2;
+		}
+		if ((modes & PARPORT_MODE_EPP) && (modes & PARPORT_MODE_ECP))
+			w_ecr(ppb_hi, 0x80);
+	}
 
 	ppa_disconnect(dev);
 	ppa_connect(dev, CONNECT_NORMAL);
···
 	if (retv)
 		return -EIO;
 
-	return device_check(dev);
+	return device_check(dev, autodetect);
 }
 
 static inline int ppa_send_command(struct scsi_cmnd *cmd)
···
 	return SUCCESS;
 }
 
-static int device_check(ppa_struct *dev)
+static int device_check(ppa_struct *dev, bool autodetect)
 {
 	/* This routine looks for a device and then attempts to use EPP
 	   to send a command. If all goes as planned then EPP is available. */
···
 	old_mode = dev->mode;
 	for (loop = 0; loop < 8; loop++) {
 		/* Attempt to use EPP for Test Unit Ready */
-		if ((ppb & 0x0007) == 0x0000)
-			dev->mode = PPA_EPP_32;
+		if (autodetect && (ppb & 0x0007) == 0x0000)
+			dev->mode = PPA_EPP_8;
 
 second_pass:
 		ppa_connect(dev, CONNECT_EPP_MAYBE);
···
 			udelay(1000);
 			ppa_disconnect(dev);
 			udelay(1000);
-			if (dev->mode == PPA_EPP_32) {
+			if (dev->mode != old_mode) {
 				dev->mode = old_mode;
 				goto second_pass;
 			}
···
 			udelay(1000);
 			ppa_disconnect(dev);
 			udelay(1000);
-			if (dev->mode == PPA_EPP_32) {
+			if (dev->mode != old_mode) {
 				dev->mode = old_mode;
 				goto second_pass;
 			}
···
 	DEFINE_WAIT(wait);
 	ppa_struct *dev, *temp;
 	int ports;
-	int modes, ppb, ppb_hi;
 	int err = -ENOMEM;
 	struct pardev_cb ppa_cb;
 
···
 	if (!dev)
 		return -ENOMEM;
 	dev->base = -1;
-	dev->mode = PPA_AUTODETECT;
+	dev->mode = mode < PPA_UNKNOWN ? mode : PPA_AUTODETECT;
 	dev->recon_tmo = PPA_RECON_TMO;
 	init_waitqueue_head(&waiting);
 	temp = find_parent();
···
 	}
 	dev->waiting = NULL;
 	finish_wait(&waiting, &wait);
-	ppb = dev->base = dev->dev->port->base;
-	ppb_hi = dev->dev->port->base_hi;
-	w_ctr(ppb, 0x0c);
-	modes = dev->dev->port->modes;
-
-	/* Mode detection works up the chain of speed
-	 * This avoids a nasty if-then-else-if-... tree
-	 */
-	dev->mode = PPA_NIBBLE;
-
-	if (modes & PARPORT_MODE_TRISTATE)
-		dev->mode = PPA_PS2;
-
-	if (modes & PARPORT_MODE_ECP) {
-		w_ecr(ppb_hi, 0x20);
-		dev->mode = PPA_PS2;
-	}
-	if ((modes & PARPORT_MODE_EPP) && (modes & PARPORT_MODE_ECP))
-		w_ecr(ppb_hi, 0x80);
+	dev->base = dev->dev->port->base;
+	w_ctr(dev->base, 0x0c);
 
 	/* Done configuration */
 

drivers/scsi/ppa.h

···
     "PS/2",
     "EPP 8 bit",
     "EPP 16 bit",
-#ifdef CONFIG_SCSI_IZIP_EPP16
-    "EPP 16 bit",
-#else
     "EPP 32 bit",
-#endif
     "Unknown"};
 
 /* other options */