flash: Only erase flash block that contain data

It wastes time to erase blocks that are already erased and it is faster
on stm32 to check first. Add a check in flash_physical_erase() on all
chips, using a common flash_is_erased() function.

BUG=none
BRANCH=snow,link
TEST=manual
Do software sync in U-Boot and see that it succeeds. This tests that
we can still erase and then boot a written image. It typically saves
a second on a full sync over i2c.

SMDK5250 # cros_test swsync -f
SF: Detected W25Q32 with page size 4 KiB, total 4 MiB
Flashing RW EC image: erasing, writing, done
Flashing RO EC image: erasing, writing, done
Full software sync completed in 22.949s
SMDK5250 #

Also see that second erase is faster:

SMDK5250 # time mkbp erase rw

time: 0.952 seconds, 952 ticks
SMDK5250 # time mkbp erase rw

time: 0.054 seconds, 54 ticks
SMDK5250 #

Change-Id: I3699577217fdbb2f212d20d150d3ca15fdff03eb
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/30851
Reviewed-by: Randall Spangler <rspangler@chromium.org>

chip/lm4/flash.c

@@ -227,11 +227,17 @@ int flash_physical_write(int offset, int size, const char *data)
 int flash_physical_erase(int offset, int size)
 {
 	LM4_FLASH_FCMISC = LM4_FLASH_FCRIS;  /* Clear previous error status */
-	LM4_FLASH_FMA = offset;
 
-	for ( ; size > 0; size -= CONFIG_FLASH_ERASE_SIZE) {
+	for ( ; size > 0; size -= CONFIG_FLASH_ERASE_SIZE,
+			offset += CONFIG_FLASH_ERASE_SIZE) {
 		int t;
 
+		/* Do nothing if already erased */
+		if (flash_is_erased(offset, CONFIG_FLASH_ERASE_SIZE))
+			continue;
+
+		LM4_FLASH_FMA = offset;
+
 #ifdef CONFIG_TASK_WATCHDOG
 		/* Reload the watchdog timer, so that erasing many flash pages
 		 * doesn't cause a watchdog reset.  May not need this now that
@@ -253,8 +259,6 @@ int flash_physical_erase(int offset, int size)
 		 * protection error */
 		if (LM4_FLASH_FCRIS & 0x0a01)
 			return EC_ERROR_UNKNOWN;
-
-		LM4_FLASH_FMA += CONFIG_FLASH_ERASE_SIZE;
 	}
 
 	return EC_SUCCESS;

chip/stm32/flash-stm32f100.c

@@ -349,7 +349,6 @@ exit_wr:
 
 int flash_physical_erase(int offset, int size)
 {
-	uint32_t address;
 	int res = EC_SUCCESS;
 
 	if (unlock(PRG_LOCK) != EC_SUCCESS)
@@ -361,13 +360,16 @@ int flash_physical_erase(int offset, int size)
 	/* set PER bit */
 	STM32_FLASH_CR |= PER;
 
-	for (address = CONFIG_FLASH_BASE + offset ;
-	     size > 0; size -= CONFIG_FLASH_ERASE_SIZE,
-	     address += CONFIG_FLASH_ERASE_SIZE) {
+	for (; size > 0; size -= CONFIG_FLASH_ERASE_SIZE,
+	     offset += CONFIG_FLASH_ERASE_SIZE) {
 		timestamp_t deadline;
 
+		/* Do nothing if already erased */
+		if (flash_is_erased(offset, CONFIG_FLASH_ERASE_SIZE))
+			continue;
+
 		/* select page to erase */
-		STM32_FLASH_AR = address;
+		STM32_FLASH_AR = CONFIG_FLASH_BASE + offset;
 
 		/* set STRT bit : start erase */
 		STM32_FLASH_CR |= STRT;

chip/stm32/flash-stm32l15x.c

@@ -235,6 +235,12 @@ int flash_physical_erase(int offset, int size)
 	     address += CONFIG_FLASH_ERASE_SIZE / sizeof(uint32_t)) {
 		timestamp_t deadline;
 
+		/*
+		 * crosbug.com/p/13066
+		 * We can't do the flash_is_erased() trick on stm32l since
+		 * bits erase to 0, not 1. Will address later if needed.
+		 */
+
 		/* Start erase */
 		*address = 0x00000000;
 

common/flash_common.c

@@ -26,6 +26,23 @@ int flash_dataptr(int offset, int size_req, int align, char **ptrp)
 	return CONFIG_FLASH_SIZE - offset;
 }
 
+/* crosbug.com/p/13066 - not supported on STM32L */
+#ifndef CHIP_VARIANT_stm32l15x
+int flash_is_erased(uint32_t offset, int size)
+{
+	uint32_t *ptr;
+
+	if (flash_dataptr(offset, size, sizeof(uint32_t), (char **)&ptr) < 0)
+		return 0;
+
+	for (size /= sizeof(uint32_t); size > 0; size -= 4, ptr++)
+		if (*ptr != -1U)
+			return 0;
+
+	return 1;
+}
+#endif
+
 int flash_write(int offset, int size, const char *data)
 {
 	if (flash_dataptr(offset, size, CONFIG_FLASH_WRITE_SIZE, NULL) < 0)

include/flash.h

@@ -31,6 +31,17 @@ static inline char *flash_physical_dataptr(int offset)
 	return (char *)(CONFIG_FLASH_BASE + offset);
 }
 
+/**
+ * Check if a region of flash is erased
+ *
+ * It is assumed that an erased region has all bits set to 1.
+ *
+ * @param offset	Flash offset to check
+ * @param size		Number of bytes to check (word-aligned)
+ * @return 1 if erased, 0 if not erased
+ */
+int flash_is_erased(uint32_t offset, int size);
+
 /**
  * Write to physical flash.
  *