[PATCH RFC 1/4] spi: spi-mem: Add set_iofv() callback

[Biju Das <biju.das.jz@xxxxxxxxxxxxxx>]

As per section 8.14 on the AT25QL128A hardware manual,
IO0..IO3 must be set to Hi-Z state for this flash for fast read quad IO.
Snippet from HW manual section 8.14:
The upper nibble of the Mode(M7-4) controls the length of the next FAST
Read Quad IO instruction through the inclusion or exclusion of the first
byte instruction code. The lower nibble bits of the Mode(M3-0) are don't
care. However, the IO pins must be high-impedance before the falling edge
of the first data out clock.

Add set_iofv() callback for configuring IO fixed values to control the
pin state.

Signed-off-by: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>
---
 drivers/spi/spi-mem.c       | 20 ++++++++++++++++++++
 include/linux/spi/spi-mem.h |  4 ++++
 2 files changed, 24 insertions(+)

diff --git a/drivers/spi/spi-mem.c b/drivers/spi/spi-mem.c
index edd7430d4c05..0cfca8c438e3 100644
--- a/drivers/spi/spi-mem.c
+++ b/drivers/spi/spi-mem.c
@@ -297,6 +297,26 @@ static void spi_mem_access_end(struct spi_mem *mem)
 		pm_runtime_put(ctlr->dev.parent);
 }
 
+/**
+ * spi_mem_set_iofv() - Set IO fixed values to control the pin state
+ * @mem: the SPI memory
+ * @val: the IO fixed values
+ *
+ * Set IO fixed values to control the pin state.
+ *
+ * Return: 0 in case of success, a negative error code otherwise.
+ */
+int spi_mem_set_iofv(struct spi_mem *mem, u32 val)
+{
+	struct spi_controller *ctlr = mem->spi->controller;
+
+	if (ctlr->mem_ops && ctlr->mem_ops->set_iofv)
+		return ctlr->mem_ops->set_iofv(mem, val);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(spi_mem_set_iofv);
+
 /**
  * spi_mem_exec_op() - Execute a memory operation
  * @mem: the SPI memory
diff --git a/include/linux/spi/spi-mem.h b/include/linux/spi/spi-mem.h
index 6b0a7dc48a4b..e50f89bf5ba9 100644
--- a/include/linux/spi/spi-mem.h
+++ b/include/linux/spi/spi-mem.h
@@ -232,6 +232,7 @@ static inline void *spi_mem_get_drvdata(struct spi_mem *mem)
  *		    limitations (can be alignment or max RX/TX size
  *		    limitations)
  * @supports_op: check if an operation is supported by the controller
+ * @set_iofv: set IO fixed values to control the pin state
  * @exec_op: execute a SPI memory operation
  * @get_name: get a custom name for the SPI mem device from the controller.
  *	      This might be needed if the controller driver has been ported
@@ -274,6 +275,7 @@ struct spi_controller_mem_ops {
 	int (*adjust_op_size)(struct spi_mem *mem, struct spi_mem_op *op);
 	bool (*supports_op)(struct spi_mem *mem,
 			    const struct spi_mem_op *op);
+	int (*set_iofv)(struct spi_mem *mem, u32 val);
 	int (*exec_op)(struct spi_mem *mem,
 		       const struct spi_mem_op *op);
 	const char *(*get_name)(struct spi_mem *mem);
@@ -367,6 +369,8 @@ int spi_mem_adjust_op_size(struct spi_mem *mem, struct spi_mem_op *op);
 bool spi_mem_supports_op(struct spi_mem *mem,
 			 const struct spi_mem_op *op);
 
+int spi_mem_set_iofv(struct spi_mem *mem, u32 val);
+
 int spi_mem_exec_op(struct spi_mem *mem,
 		    const struct spi_mem_op *op);
 
-- 
2.25.1