[PATCH v2 2/3] mtd: spi-nor: core: Allow flashes to specify MTD writesize

[Pratyush Yadav]

Some flashes like the Cypress S28 family use ECC. Under this ECC scheme,
multi-pass writes to an ECC block is not allowed. In other words, once
data is programmed to an ECC block, it can't be programmed again without
erasing it first.

Upper layers like file systems need to be given this information so they
do not cause error conditions on the flash by attempting multi-pass
programming. This can be done by setting 'writesize' in 'struct
mtd_info'.

Set the default to 1 but allow flashes to modify it in fixup hooks. If
more flashes show up with this constraint in the future it might be
worth it to add it to 'struct flash_info', but for now increasing its
size is not worth it.

Signed-off-by: Pratyush Yadav <p.yadav@xxxxxx>
---

Notes:
    New in v2.

 drivers/mtd/spi-nor/core.c | 4 +++-
 drivers/mtd/spi-nor/core.h | 3 +++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index 5bee7c8da4dc..80fbcb9c0828 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -3054,6 +3054,8 @@ static int spi_nor_init_params(struct spi_nor *nor)
 	if (!nor->params)
 		return -ENOMEM;
 
+	nor->params->writesize = 1;
+
 	spi_nor_info_init_params(nor);
 
 	spi_nor_manufacturer_init_params(nor);
@@ -3430,7 +3432,7 @@ int spi_nor_scan(struct spi_nor *nor, const char *name,
 		mtd->name = dev_name(dev);
 	mtd->priv = nor;
 	mtd->type = MTD_NORFLASH;
-	mtd->writesize = 1;
+	mtd->writesize = nor->params->writesize;
 	mtd->flags = MTD_CAP_NORFLASH;
 	mtd->size = nor->params->size;
 	mtd->_erase = spi_nor_erase;
diff --git a/drivers/mtd/spi-nor/core.h b/drivers/mtd/spi-nor/core.h
index 0a775a7b5606..413ea311e632 100644
--- a/drivers/mtd/spi-nor/core.h
+++ b/drivers/mtd/spi-nor/core.h
@@ -197,6 +197,8 @@ struct spi_nor_locking_ops {
  * @rdsr_dummy:		dummy cycles needed for Read Status Register command.
  * @rdsr_addr_nbytes:	dummy address bytes needed for Read Status Register
  *			command.
+ * @writesize		Minimal writable flash unit size. Defaults to 1. Set to
+ *			ECC unit size for ECC-ed flashes.
  * @hwcaps:		describes the read and page program hardware
  *			capabilities.
  * @reads:		read capabilities ordered by priority: the higher index
@@ -222,6 +224,7 @@ struct spi_nor_flash_parameter {
 	u32				page_size;
 	u8				rdsr_dummy;
 	u8				rdsr_addr_nbytes;
+	u32				writesize;
 
 	struct spi_nor_hwcaps		hwcaps;
 	struct spi_nor_read_command	reads[SNOR_CMD_READ_MAX];
-- 
2.28.0