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 <ben-linux@fluff.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 4 deletions

diff --git a/drivers/mfd/sm501.c b/drivers/mfd/sm501.c
index e14d70e07418..8135e4c3bf47 100644
--- a/drivers/mfd/sm501.c
+++ b/drivers/mfd/sm501.c
@@ -893,6 +893,7 @@ static int sm501_init_dev(struct sm501_devdata *sm)
 {
         resource_size_t mem_avail;
         unsigned long dramctrl;
+        unsigned long devid;
         int ret;
 
         mutex_init(&sm->clock_lock);
@@ -900,13 +901,18 @@ static int sm501_init_dev(struct sm501_devdata *sm)
 
         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);