spi: spi-mem: Introduce a capability structure

Create a spi_controller_mem_caps structure and put it within the
spi_controller structure close to the spi_controller_mem_ops
strucure. So far the only field in this structure is the support for dtr
operations, but soon we will add another parameter.

Also create a helper to parse the capabilities and check if the
requested capability has been set or not.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Pratyush Yadav <p.yadav@ti.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/linux-mtd/20220127091808.1043392-2-miquel.raynal@bootlin.com

include/linux/spi/spi-mem.h

@@ -285,6 +285,17 @@ struct spi_controller_mem_ops {
 			   unsigned long timeout_ms);
 };
 
+/**
+ * struct spi_controller_mem_caps - SPI memory controller capabilities
+ * @dtr: Supports DTR operations
+ */
+struct spi_controller_mem_caps {
+	bool dtr;
+};
+
+#define spi_mem_controller_is_capable(ctlr, cap)	\
+	((ctlr)->mem_caps && (ctlr)->mem_caps->cap)
+
 /**
  * struct spi_mem_driver - SPI memory driver
  * @spidrv: inherit from a SPI driver

include/linux/spi/spi.h

@@ -23,6 +23,7 @@ struct ptp_system_timestamp;
 struct spi_controller;
 struct spi_transfer;
 struct spi_controller_mem_ops;
+struct spi_controller_mem_caps;
 
 /*
  * INTERFACES between SPI master-side drivers and SPI slave protocol handlers,
@@ -415,6 +416,7 @@ extern struct spi_device *spi_new_ancillary_device(struct spi_device *spi, u8 ch
  * @mem_ops: 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.
+ * @mem_caps: controller capabilities for the handling of memory operations.
  * @unprepare_message: undo any work done by prepare_message().
  * @slave_abort: abort the ongoing transfer request on an SPI slave controller
  * @cs_gpios: LEGACY: array of GPIO descs to use as chip select lines; one per
@@ -639,6 +641,7 @@ struct spi_controller {
 
 	/* Optimized handlers for SPI memory-like operations. */
 	const struct spi_controller_mem_ops *mem_ops;
+	const struct spi_controller_mem_caps *mem_caps;
 
 	/* gpio chip select */
 	int			*cs_gpios;