spi: Extend the core to ease integration of SPI memory controllers

Some controllers are exposing high-level interfaces to access various
kind of SPI memories. Unfortunately they do not fit in the current
spi_controller model and usually have drivers placed in
drivers/mtd/spi-nor which are only supporting SPI NORs and not SPI
memories in general.

This is an attempt at defining a SPI memory interface which works for
all kinds of SPI memories (NORs, NANDs, SRAMs).

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Jagan Teki <jagan@openedev.com>

include/spi.h

@@ -9,6 +9,8 @@
 #ifndef _SPI_H_
 #define _SPI_H_
 
+#include <common.h>
+
 /* SPI mode flags */
 #define SPI_CPHA	BIT(0)			/* clock phase */
 #define SPI_CPOL	BIT(1)			/* clock polarity */
@@ -402,6 +404,15 @@ struct dm_spi_ops {
 	int (*xfer)(struct udevice *dev, unsigned int bitlen, const void *dout,
 		    void *din, unsigned long flags);
 
+	/**
+	 * Optimized handlers for SPI memory-like operations.
+	 *
+	 * Optimized/dedicated operations for interactions with SPI memory. This
+	 * field is optional and should only be implemented if the controller
+	 * has native support for memory like operations.
+	 */
+	const struct spi_controller_mem_ops *mem_ops;
+
 	/**
 	 * Set transfer speed.
 	 * This sets a new speed to be applied for next spi_xfer().