staging: comedi: amplc_pc236: fix invalid register access during detach

commit aaeb61a97b7159ebe30b18a422d04eeabfa8790b upstream.

`pc236_detach()` is called by the comedi core if it attempted to attach
a device and failed.  `pc236_detach()` calls `pc236_intr_disable()` if
the comedi device private data pointer (`devpriv`) is non-null.  This
test is insufficient as `pc236_intr_disable()` accesses hardware
registers and the attach routine may have failed before it has saved
their I/O base addresses.

Fix it by checking `dev->iobase` is non-zero before calling
`pc236_intr_disable()` as that means the I/O base addresses have been
saved and the hardware registers can be accessed.  It also implies the
comedi device private data pointer is valid, so there is no need to
check it.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
[Ian Abbott: This patch is for the stable 3.0 kernel.]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/staging/comedi/drivers/amplc_pc236.c b/drivers/staging/comedi/drivers/amplc_pc236.c
index 48246cd50d470fa499eca602b553e90c272158bc..b4311bf66e6d9974a2abb0575ce2b82c4dec6170 100644 (file)
--- a/drivers/staging/comedi/drivers/amplc_pc236.c
+++ b/drivers/staging/comedi/drivers/amplc_pc236.c
@@ -470,7 +470,7 @@ static int pc236_detach(struct comedi_device *dev)
 {
        printk(KERN_DEBUG "comedi%d: %s: detach\n", dev->minor,
               PC236_DRIVER_NAME);
-       if (devpriv)
+       if (dev->iobase)
                pc236_intr_disable(dev);
 
        if (dev->irq)