linux-kernel - [PATCH v2 3/3] mtd: spi-nor: add locking support for is25xxxxx device

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Date:   Sun, 28 Apr 2019 23:39:16 +0530
From:   Sagar Shrikant Kadam <sagar.kadam@...ive.com>
To:     marek.vasut@...il.com, tudor.ambarus@...rochip.com,
        dwmw2@...radead.org, computersforpeace@...il.com,
        bbrezillon@...nel.org, richard@....at
Cc:     palmer@...ive.com, paul.walmsley@...ive.com,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org,
        Sagar Shrikant Kadam <sagar.kadam@...ive.com>
Subject: [PATCH v2 3/3] mtd: spi-nor: add locking support for is25xxxxx device

The locking scheme for ISSI devices is based on stm_lock mechanism.
The is25xxxxx  devices have 4 bits for selecting the range of blocks to
be locked for write.

The current implementation, blocks entire 512 blocks of flash memory.

Signed-off-by: Sagar Shrikant Kadam <sagar.kadam@...ive.com>
---
 drivers/mtd/spi-nor/spi-nor.c | 60 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
index 81c7b3e..2dba7e9 100644
--- a/drivers/mtd/spi-nor/spi-nor.c
+++ b/drivers/mtd/spi-nor/spi-nor.c
@@ -1459,6 +1459,65 @@ static int macronix_quad_enable(struct spi_nor *nor)
 
 	return 0;
 }
+/**
+ * Lock a region of the flash.Implementation is based on stm_lock
+ * Supports the block protection bits BP{0,1,2,3} in the status register
+ * Returns negative on errors, 0 on success.
+ */
+static int issi_lock(struct spi_nor *nor, loff_t ofs, uint64_t len)
+{
+	struct mtd_info *mtd = &nor->mtd;
+	int status_old, status_new;
+	u8 mask = SR_BP3 | SR_BP2 | SR_BP1 | SR_BP0;
+	u8 shift = ffs(mask) - 1, pow, val = 0;
+	loff_t lock_len;
+	bool use_top = true;
+
+	status_old = read_sr(nor);
+
+	if (status_old < 0)
+		return status_old;
+
+	/* lock_len: length of region that should end up locked */
+	if (use_top)
+		lock_len = mtd->size - ofs;
+	else
+		lock_len = ofs + len;
+
+	/*
+	 * Need smallest pow such that:
+	 *
+	 *   1 / (2^pow) <= (len / size)
+	 *
+	 * so (assuming power-of-2 size) we do:
+	 *
+	 *   pow = ceil(log2(size / len)) = log2(size) - floor(log2(len))
+	 */
+	pow = ilog2(mtd->size) - ilog2(lock_len);
+	val = mask - (pow << shift);
+
+	if (val & ~mask)
+		return -EINVAL;
+
+	/* Don't "lock" with no region! */
+	if (!(val & mask))
+		return -EINVAL;
+
+	status_new = (status_old & ~mask & ~SR_TB) | val;
+
+	/* Disallow further writes if WP pin is asserted */
+	status_new |= SR_SRWD;
+
+	/* Don't bother if they're the same */
+	if (status_new == status_old)
+		return 0;
+
+	/* Only modify protection if it will not unlock other areas */
+	if ((status_new & mask) < (status_old & mask))
+		return -EINVAL;
+
+	return write_sr_and_check(nor, status_new, mask);
+}
 
 /**
  * issi_unlock() - clear BP[0123] write-protection.
@@ -4121,6 +4180,7 @@ int spi_nor_scan(struct spi_nor *nor, const char *name,
 	/* NOR protection support for ISSI chips */
 	if (JEDEC_MFR(info) == SNOR_MFR_ISSI ||
 	    info->flags & SPI_NOR_HAS_LOCK) {
+		nor->flash_lock = issi_lock;
 		nor->flash_unlock = issi_unlock;
 
 	}
-- 
1.9.1