SM501: Check SM501 ID register on initialisation

When binding the driver, check the ID register for a valid identity, in case
the SM501 is not functioning correctly.

Signed-off-by: Ben Dooks <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/mfd/sm501.c

···
 {
 	resource_size_t mem_avail;
 	unsigned long dramctrl;
+	unsigned long devid;
 	int ret;
 
 	mutex_init(&sm->clock_lock);
···
 
 	INIT_LIST_HEAD(&sm->devices);
 
-	dramctrl = readl(sm->regs + SM501_DRAM_CONTROL);
+	devid = readl(sm->regs + SM501_DEVICEID);
 
+	if ((devid & SM501_DEVICEID_IDMASK) != SM501_DEVICEID_SM501) {
+		dev_err(sm->dev, "incorrect device id %08lx\n", devid);
+		return -EINVAL;
+	}
+
+	dramctrl = readl(sm->regs + SM501_DRAM_CONTROL);
 	mem_avail = sm501_mem_local[(dramctrl >> 13) & 0x7];
 
-	dev_info(sm->dev, "SM501 At %p: Version %08x, %ld Mb, IRQ %d\n",
-		 sm->regs, readl(sm->regs + SM501_DEVICEID),
-		 (unsigned long)mem_avail >> 20, sm->irq);
+	dev_info(sm->dev, "SM501 At %p: Version %08lx, %ld Mb, IRQ %d\n",
+		 sm->regs, devid, (unsigned long)mem_avail >> 20, sm->irq);
 
 	sm501_dump_gate(sm);
 

include/linux/sm501-regs.h

···
 #define SM501_DEVICEID			(0x000060)
 /* 0x050100A0 */
 
+#define SM501_DEVICEID_SM501		(0x05010000)
+#define SM501_DEVICEID_IDMASK		(0xffff0000)
+
 #define SM501_PLLCLOCK_COUNT		(0x000064)
 #define SM501_MISC_TIMING		(0x000068)
 #define SM501_CURRENT_SDRAM_CLOCK	(0x00006C)