powerpc/wdrtas: Update wdrtas_get_interval to use rtas_data_buf

The buffer passed to the ibm,get-system-parameter RTAS call must be
in the RMA.  To ensure we pass an address in the RMA use rtas_data_buf
for the actual RTAS call and then copy the result to value.  We can't
just make it static because this can be compiled in as a module.

Also add the WDRTAS_SP_SPI_LEN so we don't litter '4' throughout the
function.
Signed-off-by: Mark Nelson <markn@au1.ibm.com>
Tested-by: Adrian Reber <adrian@lisas.de>
Acked-by: Utz Bacher <utz.bacher@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

drivers/watchdog/wdrtas.c

@@ -106,6 +106,8 @@ static int wdrtas_set_interval(int interval)
 	return result;
 }
 
+#define WDRTAS_SP_SPI_LEN 4
+
 /**
  * wdrtas_get_interval - returns the current watchdog interval
  * @fallback_value: value (in seconds) to use, if the RTAS call fails
@@ -119,10 +121,17 @@ static int wdrtas_set_interval(int interval)
 static int wdrtas_get_interval(int fallback_value)
 {
 	long result;
-	char value[4];
+	char value[WDRTAS_SP_SPI_LEN];
 
+	spin_lock(&rtas_data_buf_lock);
+	memset(rtas_data_buf, 0, WDRTAS_SP_SPI_LEN);
 	result = rtas_call(wdrtas_token_get_sp, 3, 1, NULL,
-			   WDRTAS_SP_SPI, (void *)__pa(&value), 4);
+			   WDRTAS_SP_SPI, __pa(rtas_data_buf),
+			   WDRTAS_SP_SPI_LEN);
+
+	memcpy(value, rtas_data_buf, WDRTAS_SP_SPI_LEN);
+	spin_unlock(&rtas_data_buf_lock);
+
 	if (value[0] != 0 || value[1] != 2 || value[3] != 0 || result < 0) {
 		printk(KERN_WARNING "wdrtas: could not get sp_spi watchdog "
 		       "timeout (%li). Continuing\n", result);