norflash: clean-up norflash.c

- Add comments to all the functions
- Simplify nor_poll_dws
- Simplify nor_word_program

Change-Id: I29c0199d2908a4fceb1ac3430fcfdd699be22bb3
Signed-off-by: Roberto Vargas <roberto.vargas@arm.com>

plat/arm/board/common/drivers/norflash/norflash.c

 /*
- * Copyright (c) 2015, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2015-2017, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -8,6 +8,14 @@
 #include <mmio.h>
 #include <norflash.h>
 
+/*
+ * This file supplies a low level interface to the vexpress NOR flash
+ * memory of juno and fvp. This memory is organized as an interleaved
+ * memory of two chips with a 16 bit word. It means that every 32 bit
+ * access is going to access to two different chips. This is very
+ * important when we send commands or read status of the chips
+ */
+
 /* Helper macros to access two flash banks in parallel */
 #define NOR_2X16(d)			((d << 16) | (d & 0xffff))
 
@@ -18,6 +26,9 @@
  */
 #define DWS_WORD_PROGRAM_RETRIES	1000
 
+/* Helper macro to detect end of command */
+#define NOR_CMD_END (NOR_DWS | NOR_DWS << 16l)
+
 /*
  * Poll Write State Machine. Return values:
  *    0      = WSM ready
@@ -25,24 +36,16 @@
  */
 static int nor_poll_dws(uintptr_t base_addr, unsigned int retries)
 {
-	uint32_t status;
-	int ret;
+	unsigned long status;
 
-	for (;;) {
+	do {
 		nor_send_cmd(base_addr, NOR_CMD_READ_STATUS_REG);
 		status = mmio_read_32(base_addr);
-		if ((status & NOR_DWS) &&
-		    (status & (NOR_DWS << 16))) {
-			ret = 0;
-			break;
-		}
-		if (retries-- == 0) {
-			ret = -EBUSY;
-			break;
-		}
-	}
+		if ((status & NOR_CMD_END) == NOR_CMD_END)
+			return 0;
+	} while (retries-- > 0);
 
-	return ret;
+	return -EBUSY;
 }
 
 void nor_send_cmd(uintptr_t base_addr, unsigned long cmd)
@@ -51,6 +54,9 @@ void nor_send_cmd(uintptr_t base_addr, unsigned long cmd)
 }
 
 /*
+ * This function programs a word in the flash. Be aware that it only
+ * can reset bits that were previously set. It cannot set bits that
+ * were previously reset. The resulting bits = old_bits & new bits.
  * Return values:
  *    0      = success
  *    -EBUSY = WSM not ready
@@ -66,10 +72,7 @@ int nor_word_program(uintptr_t base_addr, unsigned long data)
 	mmio_write_32(base_addr, data);
 
 	ret = nor_poll_dws(base_addr, DWS_WORD_PROGRAM_RETRIES);
-	if (ret != 0) {
-		goto word_program_end;
-	}
-
+	if (ret == 0) {
 		/* Full status check */
 		nor_send_cmd(base_addr, NOR_CMD_READ_STATUS_REG);
 		status = mmio_read_32(base_addr);
@@ -78,12 +81,15 @@ int nor_word_program(uintptr_t base_addr, unsigned long data)
 			nor_send_cmd(base_addr, NOR_CMD_CLEAR_STATUS_REG);
 			ret = -EPERM;
 		}
+	}
 
-word_program_end:
 	nor_send_cmd(base_addr, NOR_CMD_READ_ARRAY);
 	return ret;
 }
 
+/*
+ * Lock a full 256 block
+ */
 void nor_lock(uintptr_t base_addr)
 {
 	nor_send_cmd(base_addr, NOR_CMD_LOCK_UNLOCK);
@@ -91,10 +97,12 @@ void nor_lock(uintptr_t base_addr)
 	nor_send_cmd(base_addr, NOR_CMD_READ_ARRAY);
 }
 
+/*
+ * unlock a full 256 block
+ */
 void nor_unlock(uintptr_t base_addr)
 {
 	nor_send_cmd(base_addr, NOR_CMD_LOCK_UNLOCK);
 	mmio_write_32(base_addr, NOR_2X16(NOR_UNLOCK_BLOCK));
 	nor_send_cmd(base_addr, NOR_CMD_READ_ARRAY);
 }
-