mtd: spi-nor: add OTP support

SPI flashes sometimes have a special OTP area, which can (and is) used to
store immutable properties like board serial number or vendor assigned
network hardware addresses.

The MTD subsystem already supports accessing such areas and some (non
SPI NOR) flashes already implement support for it. It differentiates
between user and factory areas. User areas can be written by the user and
factory ones are pre-programmed and locked down by the vendor, usually
containing an "electrical serial number". This patch will only add support
for the user areas.

Lay the foundation and implement the MTD callbacks for the SPI NOR and add
necessary parameters to the flash_info structure. If a flash supports OTP
it can be added by the convenience macro OTP_INFO(). Sometimes there are
individual regions, which might have individual offsets. Therefore, it is
possible to specify the starting address of the first regions as well as
the distance between two regions (e.g. Winbond devices uses this method).

Additionally, the regions might be locked down. Once locked, no further
write access is possible.

For SPI NOR flashes the OTP area is accessed like the normal memory, e.g.
by offset addressing; except that you either have to use special read/write
commands (Winbond) or you have to enter (and exit) a specific OTP mode
(Macronix, Micron).

Thus we introduce four operations to which the MTD callbacks will be
mapped: .read(), .write(), .lock() and .is_locked(). The read and the write
ops will be given an address offset to operate on while the locking ops use
regions because locking always affects a whole region. It is up to the
flash driver to implement these ops.

Signed-off-by: Michael Walle <michael@walle.cc>
[ta: use div64_u64(), IS_ALIGNED, params->otp.org. unsigned int region,
drop comment, add rlen local variable in spi_nor_mtd_otp_lock()]
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/20210321235140.8308-2-michael@walle.cc

1 files changed, 212 insertions, 0 deletions

diff --git a/drivers/mtd/spi-nor/otp.c b/drivers/mtd/spi-nor/otp.c
new file mode 100644
index 000000000000..075b7290a95d
--- /dev/null
+++ b/drivers/mtd/spi-nor/otp.c
@@ -0,0 +1,212 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * OTP support for SPI NOR flashes
+ *
+ * Copyright (C) 2021 Michael Walle <michael@walle.cc>
+ */
+
+#include <linux/log2.h>
+#include <linux/mtd/mtd.h>
+#include <linux/mtd/spi-nor.h>
+
+#include "core.h"
+
+#define spi_nor_otp_region_len(nor) ((nor)->params->otp.org->len)
+#define spi_nor_otp_n_regions(nor) ((nor)->params->otp.org->n_regions)
+
+static loff_t spi_nor_otp_region_start(const struct spi_nor *nor, unsigned int region)
+{
+	const struct spi_nor_otp_organization *org = nor->params->otp.org;
+
+	return org->base + region * org->offset;
+}
+
+static size_t spi_nor_otp_size(struct spi_nor *nor)
+{
+	return spi_nor_otp_n_regions(nor) * spi_nor_otp_region_len(nor);
+}
+
+/* Translate the file offsets from and to OTP regions. */
+static loff_t spi_nor_otp_region_to_offset(struct spi_nor *nor, unsigned int region)
+{
+	return region * spi_nor_otp_region_len(nor);
+}
+
+static unsigned int spi_nor_otp_offset_to_region(struct spi_nor *nor, loff_t ofs)
+{
+	return div64_u64(ofs, spi_nor_otp_region_len(nor));
+}
+
+static int spi_nor_mtd_otp_info(struct mtd_info *mtd, size_t len,
+				size_t *retlen, struct otp_info *buf)
+{
+	struct spi_nor *nor = mtd_to_spi_nor(mtd);
+	const struct spi_nor_otp_ops *ops = nor->params->otp.ops;
+	unsigned int n_regions = spi_nor_otp_n_regions(nor);
+	unsigned int i;
+	int ret, locked;
+
+	if (len < n_regions * sizeof(*buf))
+		return -ENOSPC;
+
+	ret = spi_nor_lock_and_prep(nor);
+	if (ret)
+		return ret;
+
+	for (i = 0; i < n_regions; i++) {
+		buf->start = spi_nor_otp_region_to_offset(nor, i);
+		buf->length = spi_nor_otp_region_len(nor);
+
+		locked = ops->is_locked(nor, i);
+		if (locked < 0) {
+			ret = locked;
+			goto out;
+		}
+
+		buf->locked = !!locked;
+		buf++;
+	}
+
+	*retlen = n_regions * sizeof(*buf);
+
+out:
+	spi_nor_unlock_and_unprep(nor);
+
+	return ret;
+}
+
+static int spi_nor_mtd_otp_read_write(struct mtd_info *mtd, loff_t ofs,
+				      size_t total_len, size_t *retlen,
+				      u8 *buf, bool is_write)
+{
+	struct spi_nor *nor = mtd_to_spi_nor(mtd);
+	const struct spi_nor_otp_ops *ops = nor->params->otp.ops;
+	const size_t rlen = spi_nor_otp_region_len(nor);
+	loff_t rstart, rofs;
+	unsigned int region;
+	size_t len;
+	int ret;
+
+	if (ofs < 0 || ofs >= spi_nor_otp_size(nor))
+		return 0;
+
+	ret = spi_nor_lock_and_prep(nor);
+	if (ret)
+		return ret;
+
+	/* don't access beyond the end */
+	total_len = min_t(size_t, total_len, spi_nor_otp_size(nor) - ofs);
+
+	*retlen = 0;
+	while (total_len) {
+		/*
+		 * The OTP regions are mapped into a contiguous area starting
+		 * at 0 as expected by the MTD layer. This will map the MTD
+		 * file offsets to the address of an OTP region as used in the
+		 * actual SPI commands.
+		 */
+		region = spi_nor_otp_offset_to_region(nor, ofs);
+		rstart = spi_nor_otp_region_start(nor, region);
+
+		/*
+		 * The size of a OTP region is expected to be a power of two,
+		 * thus we can just mask the lower bits and get the offset into
+		 * a region.
+		 */
+		rofs = ofs & (rlen - 1);
+
+		/* don't access beyond one OTP region */
+		len = min_t(size_t, total_len, rlen - rofs);
+
+		if (is_write)
+			ret = ops->write(nor, rstart + rofs, len, buf);
+		else
+			ret = ops->read(nor, rstart + rofs, len, buf);
+		if (ret == 0)
+			ret = -EIO;
+		if (ret < 0)
+			goto out;
+
+		*retlen += ret;
+		ofs += ret;
+		buf += ret;
+		total_len -= ret;
+	}
+	ret = 0;
+
+out:
+	spi_nor_unlock_and_unprep(nor);
+	return ret;
+}
+
+static int spi_nor_mtd_otp_read(struct mtd_info *mtd, loff_t from, size_t len,
+				size_t *retlen, u8 *buf)
+{
+	return spi_nor_mtd_otp_read_write(mtd, from, len, retlen, buf, false);
+}
+
+static int spi_nor_mtd_otp_write(struct mtd_info *mtd, loff_t to, size_t len,
+				 size_t *retlen, u8 *buf)
+{
+	return spi_nor_mtd_otp_read_write(mtd, to, len, retlen, buf, true);
+}
+
+static int spi_nor_mtd_otp_lock(struct mtd_info *mtd, loff_t from, size_t len)
+{
+	struct spi_nor *nor = mtd_to_spi_nor(mtd);
+	const struct spi_nor_otp_ops *ops = nor->params->otp.ops;
+	const size_t rlen = spi_nor_otp_region_len(nor);
+	unsigned int region;
+	int ret;
+
+	if (from < 0 || (from + len) > spi_nor_otp_size(nor))
+		return -EINVAL;
+
+	/* the user has to explicitly ask for whole regions */
+	if (!IS_ALIGNED(len, rlen) || !IS_ALIGNED(from, rlen))
+		return -EINVAL;
+
+	ret = spi_nor_lock_and_prep(nor);
+	if (ret)
+		return ret;
+
+	while (len) {
+		region = spi_nor_otp_offset_to_region(nor, from);
+		ret = ops->lock(nor, region);
+		if (ret)
+			goto out;
+
+		len -= rlen;
+		from += rlen;
+	}
+
+out:
+	spi_nor_unlock_and_unprep(nor);
+
+	return ret;
+}
+
+void spi_nor_otp_init(struct spi_nor *nor)
+{
+	struct mtd_info *mtd = &nor->mtd;
+
+	if (!nor->params->otp.ops)
+		return;
+
+	if (WARN_ON(!is_power_of_2(spi_nor_otp_region_len(nor))))
+		return;
+
+	/*
+	 * We only support user_prot callbacks (yet).
+	 *
+	 * Some SPI NOR flashes like Macronix ones can be ordered in two
+	 * different variants. One with a factory locked OTP area and one where
+	 * it is left to the user to write to it. The factory locked OTP is
+	 * usually preprogrammed with an "electrical serial number". We don't
+	 * support these for now.
+	 */
+	mtd->_get_user_prot_info = spi_nor_mtd_otp_info;
+	mtd->_read_user_prot_reg = spi_nor_mtd_otp_read;
+	mtd->_write_user_prot_reg = spi_nor_mtd_otp_write;
+	mtd->_lock_user_prot_reg = spi_nor_mtd_otp_lock;
+}