[PATCH v2 04/10] block: allow block devices to implement the cdev erase operation

[Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx>]

We mainly implement cdev erase for raw flashes. Many block devices, like
NVMe, SSD or SD/MMC are also flash-based and expose a mechanism or
multiple to trigger an erase on hardware or flash translation layer
level without an accompanied write.

To make it possible to use this functionality elsewhere in barebox,
let's have the common block device layer pass through the erase
operation, so it may be implemented in a device-specific manner.

Signed-off-by: Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx>
---
v1 -> v2:
  - use newly added region_overlap_size helper in range.h
---
 common/block.c  | 34 ++++++++++++++++++++++++++++++++++
 include/block.h |  1 +
 2 files changed, 35 insertions(+)

diff --git a/common/block.c b/common/block.c
index f55da775a797..eaec454ecbb2 100644
--- a/common/block.c
+++ b/common/block.c
@@ -11,6 +11,7 @@
 #include <linux/err.h>
 #include <linux/list.h>
 #include <dma.h>
+#include <range.h>
 #include <file-list.h>
 
 LIST_HEAD(block_device_list);
@@ -380,10 +381,35 @@ static int block_op_discard_range(struct cdev *cdev, loff_t count, loff_t offset
 	return 0;
 }
 
+static __maybe_unused int block_op_erase(struct cdev *cdev, loff_t count, loff_t offset)
+{
+	struct block_device *blk = cdev->priv;
+	struct chunk *chunk, *tmp;
+	int ret;
+
+	if (!blk->ops->erase)
+		return -EOPNOTSUPP;
+
+	count >>= blk->blockbits;
+	offset >>= blk->blockbits;
+
+	list_for_each_entry_safe(chunk, tmp, &blk->buffered_blocks, list) {
+		if (region_overlap_size(offset, count, chunk->block_start, blk->rdbufsize)) {
+			ret = chunk_flush(blk, chunk);
+			if (ret < 0)
+				return ret;
+			list_move(&chunk->list, &blk->idle_blocks);
+		}
+	}
+
+	return blk->ops->erase(blk, offset, count);
+}
+
 static struct cdev_operations block_ops = {
 	.read	= block_op_read,
 #ifdef CONFIG_BLOCK_WRITE
 	.write	= block_op_write,
+	.erase = block_op_erase,
 #endif
 	.close	= block_op_close,
 	.flush	= block_op_flush,
@@ -429,6 +455,14 @@ int blockdevice_register(struct block_device *blk)
 		list_add_tail(&chunk->list, &blk->idle_blocks);
 	}
 
+	/* TODO: We currently set this to ignore ERASE_TO_FLASH, but it could
+	 * be useful to propagate the enum erase_type down into the erase
+	 * callbacks and then map ERASE_TO_FLASH here to a discard operation.
+	 * Before doing that though, we need to optimize the hardware drivers
+	 * (currently eMMC) to erase bigger regions at once
+	 */
+	blk->cdev.flags |= DEVFS_WRITE_AUTOERASE;
+
 	ret = devfs_create(&blk->cdev);
 	if (ret)
 		return ret;
diff --git a/include/block.h b/include/block.h
index a0f226c7649f..eb319b953d32 100644
--- a/include/block.h
+++ b/include/block.h
@@ -12,6 +12,7 @@ struct file_list;
 struct block_device_ops {
 	int (*read)(struct block_device *, void *buf, sector_t block, blkcnt_t num_blocks);
 	int (*write)(struct block_device *, const void *buf, sector_t block, blkcnt_t num_blocks);
+	int (*erase)(struct block_device *blk, sector_t block, blkcnt_t num_blocks);
 	int (*flush)(struct block_device *);
 };
 
-- 
2.39.2