drivers: entropy: use non-cache intermediate buffer for RNG

The CAAM hardware needs to read RNG values into a non-cache
buffer. Since the contract to Zephyr RNG functions do not
require non-cache buffers, we use an intermediate non-cache
buffer to retrieve results.

Added a Kconfig to control the size of the intermediate buffer.

Fixes #53035

Signed-off-by: David Leach <[email protected]>

Author: dleach02

drivers/entropy/Kconfig.mcux

@@ -63,3 +63,16 @@ endchoice
 choice CSPRNG_GENERATOR_CHOICE
 	default CTR_DRBG_CSPRNG_GENERATOR if ENTROPY_MCUX_TRNG
 endchoice
+
+if ENTROPY_MCUX_CAAM
+
+config ENTRY_MCUX_CAAM_POOL_SIZE
+	int "CAAM random number pool size"
+	range 4 1024
+	default 256
+	help
+	  Buffer length in bytes used to store random bytes generated by
+	  CAAM hardware. Please note, that size of the pool must be a
+	  power of 2.
+
+endif # ENTROPY_MCUX_CAAM

drivers/entropy/entropy_mcux_caam.c

@@ -17,7 +17,9 @@ struct mcux_entropy_config {
 	CAAM_Type *base;
 };
 
-static caam_job_ring_interface_t jrif __attribute__((__section__(".nocache")));
+static caam_job_ring_interface_t jrif0 __attribute__((__section__(".nocache")));
+static uint8_t rng_buff_pool[CONFIG_ENTRY_MCUX_CAAM_POOL_SIZE]
+					__attribute__((__section__(".nocache")));
 
 static int entropy_mcux_caam_get_entropy(const struct device *dev,
 					 uint8_t *buffer,
@@ -26,13 +28,26 @@ static int entropy_mcux_caam_get_entropy(const struct device *dev,
 	const struct mcux_entropy_config *config = dev->config;
 	status_t status;
 	caam_handle_t handle;
+	uint16_t read_length = 0;
+	uint16_t insert_idx = 0;
 
 	handle.jobRing = kCAAM_JobRing0;
 
-	status = CAAM_RNG_GetRandomData(
-			config->base, &handle, kCAAM_RngStateHandle0,
-			buffer, length, kCAAM_RngDataAny, NULL);
-	__ASSERT_NO_MSG(!status);
+	/*
+	 * The buffer passed to the CAAM RNG function needs to be in non-cache
+	 * memory. Use an intermediate buffer to stage the data to the user
+	 * buffer.
+	 */
+	while (insert_idx < length) {
+		read_length = MIN(sizeof(rng_buff_pool), (length - insert_idx));
+
+		status = CAAM_RNG_GetRandomData(
+				config->base, &handle, kCAAM_RngStateHandle0,
+				&rng_buff_pool[0], read_length, kCAAM_RngDataAny, NULL);
+
+		memcpy(&buffer[insert_idx], &rng_buff_pool[0], read_length);
+		insert_idx += read_length;
+	}
 
 	return 0;
 }
@@ -52,7 +67,7 @@ static int entropy_mcux_caam_init(const struct device *dev)
 	status_t status;
 
 	CAAM_GetDefaultConfig(&conf);
-	conf.jobRingInterface[0] = &jrif;
+	conf.jobRingInterface[0] = &jrif0;
 
 	status = CAAM_Init(config->base, &conf);
 	__ASSERT_NO_MSG(!status);

west.yml

@@ -93,7 +93,7 @@ manifest:
       groups:
         - hal
     - name: hal_nxp
-      revision: 3ee6020efc1f8323d0fdc85615d3477161f0aa1f
+      revision: d957472002a3758154f402e982d95ce90cf58e12
       path: modules/hal/nxp
       groups:
         - hal