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Subject[PATCH v5 1/6] mtd: spi-nor: Fix clearing of QE bit on lock()/unlock()
Date
From: Tudor Ambarus <tudor.ambarus@microchip.com>

Make sure that when doing a lock() or an unlock() operation we don't clear
the QE bit from Status Register 2.

JESD216 revB or later offers information about the *default* Status
Register commands to use (see BFPT DWORDS[15], bits 22:20). In this
standard, Status Register 1 refers to the first data byte transferred on a
Read Status (05h) or Write Status (01h) command. Status register 2 refers
to the byte read using instruction 35h. Status register 2 is the second
byte transferred in a Write Status (01h) command.

Industry naming and definitions of these Status Registers may differ.
The definitions are described in JESD216B, BFPT DWORDS[15], bits 22:20.
There are cases in which writing only one byte to the Status Register 1
has the side-effect of clearing Status Register 2 and implicitly the Quad
Enable bit. This side-effect is hit just by the
BFPT_DWORD15_QER_SR2_BIT1_BUGGY and BFPT_DWORD15_QER_SR2_BIT1 cases.

Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Vignesh Raghavendra <vigneshr@ti.com>
---
drivers/mtd/spi-nor/spi-nor.c | 120 ++++++++++++++++++++++++++++++++++++++++--
include/linux/mtd/spi-nor.h | 3 ++
2 files changed, 118 insertions(+), 5 deletions(-)

diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
index 9960e09136ce..d696334f25f0 100644
--- a/drivers/mtd/spi-nor/spi-nor.c
+++ b/drivers/mtd/spi-nor/spi-nor.c
@@ -959,12 +959,19 @@ static int spi_nor_write_sr(struct spi_nor *nor, const u8 *sr, size_t len)
return spi_nor_wait_till_ready(nor);
}

-/* Write status register and ensure bits in mask match written values */
-static int spi_nor_write_sr_and_check(struct spi_nor *nor, u8 status_new)
+/**
+ * spi_nor_write_sr1_and_check() - Write one byte to the Status Register 1 and
+ * ensure that the byte written match the received value.
+ * @nor: pointer to a 'struct spi_nor'.
+ * @sr1: byte value to be written to the Status Register.
+ *
+ * Return: 0 on success, -errno otherwise.
+ */
+static int spi_nor_write_sr1_and_check(struct spi_nor *nor, u8 sr1)
{
int ret;

- nor->bouncebuf[0] = status_new;
+ nor->bouncebuf[0] = sr1;

ret = spi_nor_write_sr(nor, nor->bouncebuf, 1);
if (ret)
@@ -974,8 +981,73 @@ static int spi_nor_write_sr_and_check(struct spi_nor *nor, u8 status_new)
if (ret)
return ret;

- if (nor->bouncebuf[0] != status_new) {
- dev_dbg(nor->dev, "SR: read back test failed\n");
+ if (nor->bouncebuf[0] != sr1) {
+ dev_dbg(nor->dev, "SR1: read back test failed\n");
+ return -EIO;
+ }
+
+ return 0;
+}
+
+/**
+ * spi_nor_write_16bit_sr_and_check() - Write the Status Register 1 and the
+ * Status Register 2 in one shot. Ensure that the byte written in the Status
+ * Register 1 match the received value, and that the 16-bit Write did not
+ * affect what was already in the Status Register 2.
+ * @nor: pointer to a 'struct spi_nor'.
+ * @sr1: byte value to be written to the Status Register 1.
+ *
+ * Return: 0 on success, -errno otherwise.
+ */
+static int spi_nor_write_16bit_sr_and_check(struct spi_nor *nor, u8 sr1)
+{
+ int ret;
+ u8 *sr_cr = nor->bouncebuf;
+ u8 cr_written;
+
+ /* Make sure we don't overwrite the contents of Status Register 2. */
+ if (!(nor->flags & SNOR_F_NO_READ_CR)) {
+ ret = spi_nor_read_cr(nor, &sr_cr[1]);
+ if (ret)
+ return ret;
+ } else if (nor->params.quad_enable) {
+ /*
+ * If the Status Register 2 Read command (35h) is not
+ * supported, we should at least be sure we don't
+ * change the value of the SR2 Quad Enable bit.
+ *
+ * We can safely assume that when the Quad Enable method is
+ * set, the value of the QE bit is one, as a consequence of the
+ * nor->params.quad_enable() call.
+ *
+ * We can safely assume that the Quad Enable bit is present in
+ * the Status Register 2 at BIT(1). According to the JESD216
+ * revB standard, BFPT DWORDS[15], bits 22:20, the 16-bit
+ * Write Status (01h) command is available just for the cases
+ * in which the QE bit is described in SR2 at BIT(1).
+ */
+ sr_cr[1] = CR_QUAD_EN_SPAN;
+ } else {
+ sr_cr[1] = 0;
+ }
+
+ sr_cr[0] = sr1;
+
+ ret = spi_nor_write_sr(nor, sr_cr, 2);
+ if (ret)
+ return ret;
+
+ if (nor->flags & SNOR_F_NO_READ_CR)
+ return 0;
+
+ cr_written = sr_cr[1];
+
+ ret = spi_nor_read_cr(nor, &sr_cr[1]);
+ if (ret)
+ return ret;
+
+ if (cr_written != sr_cr[1]) {
+ dev_dbg(nor->dev, "CR: read back test failed\n");
return -EIO;
}

@@ -983,6 +1055,23 @@ static int spi_nor_write_sr_and_check(struct spi_nor *nor, u8 status_new)
}

/**
+ * spi_nor_write_sr_and_check() - Write the Status Register 1 and ensure that
+ * the byte written match the received value without affecting other bits in the
+ * Status Register 1 and 2.
+ * @nor: pointer to a 'struct spi_nor'.
+ * @sr1: byte value to be written to the Status Register.
+ *
+ * Return: 0 on success, -errno otherwise.
+ */
+static int spi_nor_write_sr_and_check(struct spi_nor *nor, u8 sr1)
+{
+ if (nor->flags & SNOR_F_HAS_16BIT_SR)
+ return spi_nor_write_16bit_sr_and_check(nor, sr1);
+
+ return spi_nor_write_sr1_and_check(nor, sr1);
+}
+
+/**
* spi_nor_write_sr2() - Write the Status Register 2 using the
* SPINOR_OP_WRSR2 (3eh) command.
* @nor: pointer to 'struct spi_nor'.
@@ -3634,19 +3723,38 @@ static int spi_nor_parse_bfpt(struct spi_nor *nor,
break;

case BFPT_DWORD15_QER_SR2_BIT1_BUGGY:
+ /*
+ * Writing only one byte to the Status Register has the
+ * side-effect of clearing Status Register 2.
+ */
case BFPT_DWORD15_QER_SR2_BIT1_NO_RD:
+ /*
+ * Read Configuration Register (35h) instruction is not
+ * supported.
+ */
+ nor->flags |= SNOR_F_HAS_16BIT_SR | SNOR_F_NO_READ_CR;
params->quad_enable = spansion_no_read_cr_quad_enable;
break;

case BFPT_DWORD15_QER_SR1_BIT6:
+ nor->flags &= ~SNOR_F_HAS_16BIT_SR;
params->quad_enable = macronix_quad_enable;
break;

case BFPT_DWORD15_QER_SR2_BIT7:
+ nor->flags &= ~SNOR_F_HAS_16BIT_SR;
params->quad_enable = sr2_bit7_quad_enable;
break;

case BFPT_DWORD15_QER_SR2_BIT1:
+ /*
+ * JESD216 rev B or later does not specify if writing only one
+ * byte to the Status Register clears or not the Status
+ * Register 2, so let's be cautious and keep the default
+ * assumption of a 16-bit Write Status (01h) command.
+ */
+ nor->flags |= SNOR_F_HAS_16BIT_SR;
+
params->quad_enable = spansion_read_cr_quad_enable;
break;

@@ -4613,6 +4721,8 @@ static void spi_nor_info_init_params(struct spi_nor *nor)
params->quad_enable = spansion_read_cr_quad_enable;
params->set_4byte = spansion_set_4byte;
params->setup = spi_nor_default_setup;
+ /* Default to 16-bit Write Status (01h) Command */
+ nor->flags |= SNOR_F_HAS_16BIT_SR;

/* Set SPI NOR sizes. */
params->size = (u64)info->sector_size * info->n_sectors;
diff --git a/include/linux/mtd/spi-nor.h b/include/linux/mtd/spi-nor.h
index d1d736d3c8ab..d6ec55cc6d97 100644
--- a/include/linux/mtd/spi-nor.h
+++ b/include/linux/mtd/spi-nor.h
@@ -243,6 +243,9 @@ enum spi_nor_option_flags {
SNOR_F_4B_OPCODES = BIT(6),
SNOR_F_HAS_4BAIT = BIT(7),
SNOR_F_HAS_LOCK = BIT(8),
+ SNOR_F_HAS_16BIT_SR = BIT(9),
+ SNOR_F_NO_READ_CR = BIT(10),
+
};

/**
--
2.9.5
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