hwrng: Return errors to upper levels in pseries-rng.c

We don't expect to get errors from the hypervisor when reading the rng,
but if we do we should pass the error up to the hwrng driver. Otherwise
the hwrng driver will continue calling us forever.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

drivers/char/hw_random/pseries-rng.c

@@ -17,6 +17,9 @@
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
  */
 
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/hw_random.h>
 #include <asm/vio.h>
@@ -25,10 +28,15 @@
 
 static int pseries_rng_data_read(struct hwrng *rng, u32 *data)
 {
-	if (plpar_hcall(H_RANDOM, (unsigned long *)data) != H_SUCCESS) {
-		printk(KERN_ERR "pseries rng hcall error\n");
-		return 0;
+	int rc;
+
+	rc = plpar_hcall(H_RANDOM, (unsigned long *)data);
+	if (rc != H_SUCCESS) {
+		pr_err_ratelimited("H_RANDOM call failed %d\n", rc);
+		return -EIO;
 	}
+
+	/* The hypervisor interface returns 64 bits */
 	return 8;
 }