drivers: flashdisk: implement basic write caching

Cache written data to avoid rewriting same flash page multiple times
when writing subsequent flash pages. The cache is used for reads to
account for reading not yet committed (i.e. dirty) page data. Speeding
up reads is not intention of this patch and therefore the read path
does not modify cache state.

Fixes: zephyrproject-rtos#30212

Signed-off-by: Tomasz Moń <[email protected]>

Author: tmon-nordic

drivers/disk/flashdisk.c

@@ -28,12 +28,11 @@ struct flashdisk_data {
 	const size_t size;
 	const size_t sector_size;
 	size_t page_size;
+	off_t cached_addr;
+	bool cache_valid;
+	bool cache_dirty;
 };
 
-/* calculate number of blocks required for a given size */
-#define GET_NUM_BLOCK(total_size, block_size) \
-	((total_size + block_size - 1) / block_size)
-
 #define GET_SIZE_TO_BOUNDARY(start, block_size) \
 	(block_size - (start & (block_size - 1)))
 
@@ -83,6 +82,11 @@ static int disk_flash_access_init(struct disk_info *disk)
 		return -ENOMEM;
 	}
 
+	if (ctx->cache_valid && ctx->cache_dirty) {
+		LOG_ERR("Discarding %s dirty cache", disk->name);
+		ctx->cache_valid = false;
+	}
+
 	return 0;
 }
 
@@ -109,8 +113,8 @@ static int disk_flash_access_read(struct disk_info *disk, uint8_t *buff,
 	struct flashdisk_data *ctx;
 	off_t fl_addr;
 	uint32_t remaining;
+	uint32_t offset;
 	uint32_t len;
-	uint32_t num_read;
 
 	ctx = CONTAINER_OF(disk, struct flashdisk_data, info);
 
@@ -120,118 +124,125 @@ static int disk_flash_access_read(struct disk_info *disk, uint8_t *buff,
 
 	fl_addr = ctx->offset + start_sector * ctx->sector_size;
 	remaining = (sector_count * ctx->sector_size);
-	len = ctx->page_size;
-	num_read = GET_NUM_BLOCK(remaining, ctx->page_size);
 
-	for (uint32_t i = 0; i < num_read; i++) {
-		if (remaining < ctx->page_size) {
+	/* Operate on page addresses to easily check for cached data */
+	offset = fl_addr & (ctx->page_size - 1);
+	fl_addr = ROUND_DOWN(fl_addr, ctx->page_size);
+
+	/* Read up to page boundary on first iteration */
+	len = ctx->page_size - offset;
+	while (remaining) {
+		if (remaining < len) {
 			len = remaining;
 		}
 
-		if (flash_read(disk->dev, fl_addr, buff, len) < 0) {
+		if (ctx->cache_valid && ctx->cached_addr == fl_addr) {
+			memcpy(buff, &ctx->cache[offset], len);
+		} else if (flash_read(disk->dev, fl_addr + offset, buff, len) < 0) {
 			return -EIO;
 		}
 
-		fl_addr += len;
-		buff += len;
+		fl_addr += ctx->page_size;
 		remaining -= len;
+		buff += len;
+
+		/* Try to read whole page on next iteration */
+		len = ctx->page_size;
+		offset = 0;
 	}
 
 	return 0;
 }
 
-/* This performs read-copy into an output buffer */
-static int read_copy_flash_block(struct disk_info *disk,
-				 off_t start_addr,
-				 uint32_t size,
-				 const void *src_buff,
-				 uint8_t *dest_buff)
+static int flashdisk_cache_commit(struct flashdisk_data *ctx)
 {
-	struct flashdisk_data *ctx;
-	off_t fl_addr;
-	uint32_t offset;
-	uint32_t remaining;
-
-	ctx = CONTAINER_OF(disk, struct flashdisk_data, info);
-
-	/* adjust offset if starting address is not erase-aligned address */
-	offset = start_addr & (ctx->page_size - 1);
-
-	/* align starting address to page boundary */
-	fl_addr = ROUND_DOWN(start_addr, ctx->page_size);
-
-	if (offset > 0) {
-		/* read page contents prior to user data */
-		if (flash_read(disk->dev, fl_addr, dest_buff, offset) < 0) {
-			return -EIO;
-		}
+	if (!ctx->cache_valid || !ctx->cache_dirty) {
+		/* Either no cached data or cache matches flash data */
+		return 0;
 	}
 
-	/* write user data in page buffer */
-	memcpy(dest_buff + offset, src_buff, size);
+	if (flash_erase(ctx->info.dev, ctx->cached_addr, ctx->page_size) < 0) {
+		return -EIO;
+	}
 
-	remaining = ctx->page_size - (offset + size);
-	if (remaining) {
-		/* read page contents after user data */
-		if (flash_read(disk->dev, start_addr + size,
-				&dest_buff[offset + size], remaining) < 0) {
-			return -EIO;
-		}
+	/* write data to flash */
+	if (flash_write(ctx->info.dev, ctx->cached_addr, ctx->cache, ctx->page_size) < 0) {
+		return -EIO;
 	}
 
+	ctx->cache_dirty = false;
 	return 0;
 }
 
-static int overwrite_flash_block(struct disk_info *disk, off_t fl_addr,
-				 const void *buff)
+static int flashdisk_cache_load(struct flashdisk_data *ctx, off_t fl_addr)
 {
-	struct flashdisk_data *ctx;
+	int rc;
 
-	ctx = CONTAINER_OF(disk, struct flashdisk_data, info);
+	__ASSERT_NO_MSG((fl_addr & (ctx->page_size - 1)) == 0);
 
-	if (flash_erase(disk->dev, fl_addr, ctx->page_size) < 0) {
-		return -EIO;
+	if (ctx->cache_valid) {
+		if (ctx->cached_addr == fl_addr) {
+			/* Page is already cached */
+			return 0;
+		}
+		/* Different page is in cache, commit it first */
+		rc = flashdisk_cache_commit(ctx);
+		if (rc < 0) {
+			/* Failed to commit dirty page, abort */
+			return rc;
+		}
 	}
 
-	/* write data to flash */
-	if (flash_write(disk->dev, fl_addr, buff, ctx->page_size) < 0) {
-		return -EIO;
+	/* Load page into cache */
+	ctx->cache_valid = false;
+	ctx->cache_dirty = false;
+	ctx->cached_addr = fl_addr;
+	rc = flash_read(ctx->info.dev, fl_addr, ctx->cache, ctx->page_size);
+	if (rc == 0) {
+		/* Successfully loaded into cache, mark as valid */
+		ctx->cache_valid = true;
+		return 0;
 	}
 
-	return 0;
+	return -EIO;
 }
 
 /* input size is either less or equal to a block size (ctx->page_size)
  * and write data never spans across adjacent blocks.
  */
-static int update_flash_block(struct disk_info *disk, off_t start_addr,
-			      uint32_t size, const void *buff)
+static int flashdisk_cache_write(struct flashdisk_data *ctx, off_t start_addr,
+				uint32_t size, const void *buff)
 {
-	struct flashdisk_data *ctx;
-	off_t fl_addr;
 	int rc;
+	off_t fl_addr;
+	uint32_t offset;
 
-	ctx = CONTAINER_OF(disk, struct flashdisk_data, info);
+	/* adjust offset if starting address is not erase-aligned address */
+	offset = start_addr & (ctx->page_size - 1);
 
-	/* always align starting address for flash write operation */
+	/* always align starting address for flash cache operations */
 	fl_addr = ROUND_DOWN(start_addr, ctx->page_size);
 
 	/* when writing full page the address must be page aligned
 	 * when writing partial page user data must be within a single page
 	 */
 	__ASSERT_NO_MSG(fl_addr + ctx->page_size >= start_addr + size);
 
-	if (size == ctx->page_size) {
-		rc = overwrite_flash_block(disk, fl_addr, buff);
-	} else {
-		/* partial block, perform read-copy with user data */
-		rc = read_copy_flash_block(disk, start_addr, size, buff, ctx->cache);
-		if (rc == 0) {
-			rc = overwrite_flash_block(disk, fl_addr, ctx->cache);
-		}
+	rc = flashdisk_cache_load(ctx, fl_addr);
+	if (rc < 0) {
+		return rc;
 	}
 
-	return rc == 0 ? 0 : -EIO;
+	/* Do not mark cache as dirty if data to be written matches cache.
+	 * If cache is already dirty, copy data to cache without compare.
+	 */
+	if (ctx->cache_dirty || memcmp(&ctx->cache[offset], buff, size)) {
+		/* Update cache and mark it as dirty */
+		memcpy(&ctx->cache[offset], buff, size);
+		ctx->cache_dirty = true;
+	}
+
+	return 0;
 }
 
 static int disk_flash_access_write(struct disk_info *disk, const uint8_t *buff,
@@ -261,7 +272,7 @@ static int disk_flash_access_write(struct disk_info *disk, const uint8_t *buff,
 		block_bnd = block_bnd & ~(ctx->page_size - 1);
 		if ((fl_addr + remaining) <= block_bnd) {
 			/* not over block boundary (a partial block also) */
-			if (update_flash_block(disk, fl_addr, remaining, buff) < 0) {
+			if (flashdisk_cache_write(ctx, fl_addr, remaining, buff) < 0) {
 				return -EIO;
 			}
 			return 0;
@@ -271,7 +282,7 @@ static int disk_flash_access_write(struct disk_info *disk, const uint8_t *buff,
 		size = GET_SIZE_TO_BOUNDARY(fl_addr, ctx->page_size);
 
 		/* write first partial block */
-		if (update_flash_block(disk, fl_addr, size, buff) < 0) {
+		if (flashdisk_cache_write(ctx, fl_addr, size, buff) < 0) {
 			return -EIO;
 		}
 
@@ -286,7 +297,7 @@ static int disk_flash_access_write(struct disk_info *disk, const uint8_t *buff,
 			break;
 		}
 
-		if (update_flash_block(disk, fl_addr, ctx->page_size, buff) < 0) {
+		if (flashdisk_cache_write(ctx, fl_addr, ctx->page_size, buff) < 0) {
 			return -EIO;
 		}
 
@@ -297,7 +308,7 @@ static int disk_flash_access_write(struct disk_info *disk, const uint8_t *buff,
 
 	/* remaining partial block */
 	if (remaining) {
-		if (update_flash_block(disk, fl_addr, remaining, buff) < 0) {
+		if (flashdisk_cache_write(ctx, fl_addr, remaining, buff) < 0) {
 			return -EIO;
 		}
 	}
@@ -313,7 +324,7 @@ static int disk_flash_access_ioctl(struct disk_info *disk, uint8_t cmd, void *bu
 
 	switch (cmd) {
 	case DISK_IOCTL_CTRL_SYNC:
-		return 0;
+		return flashdisk_cache_commit(ctx);
 	case DISK_IOCTL_GET_SECTOR_COUNT:
 		*(uint32_t *)buff = ctx->size / ctx->sector_size;
 		return 0;