isdn/capi: make reset_ctr op truly optional

The CAPI controller operation reset_ctr is marked as optional, and
not all drivers do implement it. Add a check to the kernel CAPI
whether it exists before trying to call it.

Signed-off-by: Tilman Schmidt <tilman@imap.cc>
Acked-by: Karsten Keil <isdn@linux-pingi.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/isdn/capi/kcapi.c b/drivers/isdn/capi/kcapi.c
index bd00dceacaf0..bde3c88b8b27 100644
--- a/drivers/isdn/capi/kcapi.c
+++ b/drivers/isdn/capi/kcapi.c
@@ -1147,6 +1147,12 @@ load_unlock_out:
                 if (ctr->state == CAPI_CTR_DETECTED)
                         goto reset_unlock_out;
 
+                if (ctr->reset_ctr == NULL) {
+                        printk(KERN_DEBUG "kcapi: reset: no reset function\n");
+                        retval = -ESRCH;
+                        goto reset_unlock_out;
+                }
+
                 ctr->reset_ctr(ctr);
 
                 retval = wait_on_ctr_state(ctr, CAPI_CTR_DETECTED);