[PATCH v4 4/9] mtd: spi-nor-core: Add support for volatile QE bit

[tkuw584924 at gmail.com]

From: Takahiro Kuwano <Takahiro.Kuwano at infineon.com>

Some of Spansion/Cypress chips support volatile version of configuration
registers and it is recommended to update volatile registers in the field
application due to a risk of the non-volatile registers corruption by
power interrupt. This patch adds a function to set Quad Enable bit in CFR1
volatile.

Signed-off-by: Takahiro Kuwano <Takahiro.Kuwano at infineon.com>
---
 drivers/mtd/spi/spi-nor-core.c | 53 ++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/drivers/mtd/spi/spi-nor-core.c b/drivers/mtd/spi/spi-nor-core.c
index 2803536ed5..624e730524 100644
--- a/drivers/mtd/spi/spi-nor-core.c
+++ b/drivers/mtd/spi/spi-nor-core.c
@@ -1576,6 +1576,59 @@ static int spansion_read_cr_quad_enable(struct spi_nor *nor)
 	return 0;
 }
 
+/**
+ * spansion_quad_enable_volatile() - enable Quad I/O mode in volatile register.
+ * @nor:	pointer to a 'struct spi_nor'
+ * @addr_base:	base address of register (can be >0 in multi-die parts)
+ * @dummy:	number of dummy cycles for register read
+ *
+ * It is recommended to update volatile registers in the field application due
+ * to a risk of the non-volatile registers corruption by power interrupt. This
+ * function sets Quad Enable bit in CFR1 volatile.
+ *
+ * Return: 0 on success, -errno otherwise.
+ */
+static int spansion_quad_enable_volatile(struct spi_nor *nor, u32 addr_base,
+					 u8 dummy)
+{
+	u32 addr = addr_base | SPINOR_REG_ADDR_CFR1V;
+
+	u8 cr;
+	int ret;
+
+	/* Check current Quad Enable bit value. */
+	ret = spansion_read_any_reg(nor, addr, dummy, &cr);
+	if (ret < 0) {
+		dev_dbg(nor->dev,
+			"error while reading configuration register\n");
+		return -EINVAL;
+	}
+
+	if (cr & CR_QUAD_EN_SPAN)
+		return 0;
+
+	cr |= CR_QUAD_EN_SPAN;
+
+	write_enable(nor);
+
+	ret = spansion_write_any_reg(nor, addr, cr);
+
+	if (ret < 0) {
+		dev_dbg(nor->dev,
+			"error while writing configuration register\n");
+		return -EINVAL;
+	}
+
+	/* Read back and check it. */
+	ret = spansion_read_any_reg(nor, addr, dummy, &cr);
+	if (ret || !(cr & CR_QUAD_EN_SPAN)) {
+		dev_dbg(nor->dev, "Spansion Quad bit not set\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 #if CONFIG_IS_ENABLED(SPI_FLASH_SFDP_SUPPORT)
 /**
  * spansion_no_read_cr_quad_enable() - set QE bit in Configuration Register.
-- 
2.25.1