hwrng: imx-rngc - simpler check for available random bytes

The "level" field in the status register contains the number of random
bytes that are available in the FIFO.  Use GENMASK to extract this field.
We only want to check if level is 0 or if we can read another byte.
There's no need for the shift or the level variable.
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/char/hw_random/imx-rngc.c

@@ -17,6 +17,7 @@
 #include <linux/hw_random.h>
 #include <linux/completion.h>
 #include <linux/io.h>
+#include <linux/bitfield.h>
 
 #define RNGC_VER_ID			0x0000
 #define RNGC_COMMAND			0x0004
@@ -44,8 +45,7 @@
 #define RNGC_CTRL_AUTO_SEED		0x00000010
 
 #define RNGC_STATUS_ERROR		0x00010000
-#define RNGC_STATUS_FIFO_LEVEL_MASK	0x00000f00
-#define RNGC_STATUS_FIFO_LEVEL_SHIFT	8
+#define RNGC_STATUS_FIFO_LEVEL_MASK	GENMASK(11, 8)
 #define RNGC_STATUS_SEED_DONE		0x00000020
 #define RNGC_STATUS_ST_DONE		0x00000010
 
@@ -122,7 +122,6 @@ static int imx_rngc_read(struct hwrng *rng, void *data, size_t max, bool wait)
 {
 	struct imx_rngc *rngc = container_of(rng, struct imx_rngc, rng);
 	unsigned int status;
-	unsigned int level;
 	int retval = 0;
 
 	while (max >= sizeof(u32)) {
@@ -132,11 +131,7 @@ static int imx_rngc_read(struct hwrng *rng, void *data, size_t max, bool wait)
 		if (status & RNGC_STATUS_ERROR)
 			break;
 
-		/* how many random numbers are in FIFO? [0-16] */
-		level = (status & RNGC_STATUS_FIFO_LEVEL_MASK) >>
-			RNGC_STATUS_FIFO_LEVEL_SHIFT;
-
-		if (level) {
+		if (status & RNGC_STATUS_FIFO_LEVEL_MASK) {
 			/* retrieve a random number from FIFO */
 			*(u32 *)data = readl(rngc->base + RNGC_FIFO);