mtd: mchp23k256: Add driver for this SPI SRAM device

The Microchip 23k256 is a 32K Byte SRAM connected via SPI.

Signed-off-by: Andrew Lunn <[e-mail]>
Reviewed-by: Boris Brezillon <[e-mail]>
Reviewed-by: Cyrille Pitchen <[e-mail]>
[Brian: fixed copyright to be in this millenium]
Signed-off-by: Brian Norris <[e-mail]>

drivers/mtd/devices/Kconfig

···
 	  if you want to specify device partitioning or to use a device which
 	  doesn't support the JEDEC ID instruction.
 
+config MTD_MCHP23K256
+	tristate "Microchip 23K256 SRAM"
+	depends on SPI_MASTER
+	help
+	  This enables access to Microchip 23K256 SRAM chips, using SPI.
+
+	  Set up your spi devices with the right board-specific
+	  platform data, or a device tree description if you want to
+	  specify device partitioning
+
 config MTD_SPEAR_SMI
 	tristate "SPEAR MTD NOR Support through SMI controller"
 	depends on PLAT_SPEAR

drivers/mtd/devices/Makefile

···
 obj-$(CONFIG_MTD_BLOCK2MTD)	+= block2mtd.o
 obj-$(CONFIG_MTD_DATAFLASH)	+= mtd_dataflash.o
 obj-$(CONFIG_MTD_M25P80)	+= m25p80.o
+obj-$(CONFIG_MTD_MCHP23K256)	+= mchp23k256.o
 obj-$(CONFIG_MTD_SPEAR_SMI)	+= spear_smi.o
 obj-$(CONFIG_MTD_SST25L)	+= sst25l.o
 obj-$(CONFIG_MTD_BCM47XXSFLASH)	+= bcm47xxsflash.o

drivers/mtd/devices/mchp23k256.c

···
+/*
+ * mchp23k256.c
+ *
+ * Driver for Microchip 23k256 SPI RAM chips
+ *
+ * Copyright © 2016 Andrew Lunn <[e-mail]>
+ *
+ * This code is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/mtd/mtd.h>
+#include <linux/mtd/partitions.h>
+#include <linux/mutex.h>
+#include <linux/sched.h>
+#include <linux/sizes.h>
+#include <linux/spi/flash.h>
+#include <linux/spi/spi.h>
+
+struct mchp23k256_flash {
+	struct spi_device	*spi;
+	struct mutex		lock;
+	struct mtd_info		mtd;
+};
+
+#define MCHP23K256_CMD_WRITE_STATUS	0x01
+#define MCHP23K256_CMD_WRITE		0x02
+#define MCHP23K256_CMD_READ		0x03
+#define MCHP23K256_MODE_SEQ		BIT(6)
+
+#define to_mchp23k256_flash(x) container_of(x, struct mchp23k256_flash, mtd)
+
+static int mchp23k256_write(struct mtd_info *mtd, loff_t to, size_t len,
+			    size_t *retlen, const unsigned char *buf)
+{
+	struct mchp23k256_flash *flash = to_mchp23k256_flash(mtd);
+	struct spi_transfer transfer[2] = {};
+	struct spi_message message;
+	unsigned char command[3];
+
+	spi_message_init(&message);
+
+	command[0] = MCHP23K256_CMD_WRITE;
+	command[1] = to >> 8;
+	command[2] = to;
+
+	transfer[0].tx_buf = command;
+	transfer[0].len = sizeof(command);
+	spi_message_add_tail(&transfer[0], &message);
+
+	transfer[1].tx_buf = buf;
+	transfer[1].len = len;
+	spi_message_add_tail(&transfer[1], &message);
+
+	mutex_lock(&flash->lock);
+
+	spi_sync(flash->spi, &message);
+
+	if (retlen && message.actual_length > sizeof(command))
+		*retlen += message.actual_length - sizeof(command);
+
+	mutex_unlock(&flash->lock);
+	return 0;
+}
+
+static int mchp23k256_read(struct mtd_info *mtd, loff_t from, size_t len,
+			   size_t *retlen, unsigned char *buf)
+{
+	struct mchp23k256_flash *flash = to_mchp23k256_flash(mtd);
+	struct spi_transfer transfer[2] = {};
+	struct spi_message message;
+	unsigned char command[3];
+
+	spi_message_init(&message);
+
+	memset(&transfer, 0, sizeof(transfer));
+	command[0] = MCHP23K256_CMD_READ;
+	command[1] = from >> 8;
+	command[2] = from;
+
+	transfer[0].tx_buf = command;
+	transfer[0].len = sizeof(command);
+	spi_message_add_tail(&transfer[0], &message);
+
+	transfer[1].rx_buf = buf;
+	transfer[1].len = len;
+	spi_message_add_tail(&transfer[1], &message);
+
+	mutex_lock(&flash->lock);
+
+	spi_sync(flash->spi, &message);
+
+	if (retlen && message.actual_length > sizeof(command))
+		*retlen += message.actual_length - sizeof(command);
+
+	mutex_unlock(&flash->lock);
+	return 0;
+}
+
+/*
+ * Set the device into sequential mode. This allows read/writes to the
+ * entire SRAM in a single operation
+ */
+static int mchp23k256_set_mode(struct spi_device *spi)
+{
+	struct spi_transfer transfer = {};
+	struct spi_message message;
+	unsigned char command[2];
+
+	spi_message_init(&message);
+
+	command[0] = MCHP23K256_CMD_WRITE_STATUS;
+	command[1] = MCHP23K256_MODE_SEQ;
+
+	transfer.tx_buf = command;
+	transfer.len = sizeof(command);
+	spi_message_add_tail(&transfer, &message);
+
+	return spi_sync(spi, &message);
+}
+
+static int mchp23k256_probe(struct spi_device *spi)
+{
+	struct mchp23k256_flash *flash;
+	struct flash_platform_data *data;
+	int err;
+
+	flash = devm_kzalloc(&spi->dev, sizeof(*flash), GFP_KERNEL);
+	if (!flash)
+		return -ENOMEM;
+
+	flash->spi = spi;
+	mutex_init(&flash->lock);
+	spi_set_drvdata(spi, flash);
+
+	err = mchp23k256_set_mode(spi);
+	if (err)
+		return err;
+
+	data = dev_get_platdata(&spi->dev);
+
+	flash->mtd.dev.parent	= &spi->dev;
+	flash->mtd.type		= MTD_RAM;
+	flash->mtd.flags	= MTD_CAP_RAM;
+	flash->mtd.writesize	= 1;
+	flash->mtd.size		= SZ_32K;
+	flash->mtd._read	= mchp23k256_read;
+	flash->mtd._write	= mchp23k256_write;
+
+	err = mtd_device_parse_register(&flash->mtd, NULL, NULL,
+					data ? data->parts : NULL,
+					data ? data->nr_parts : 0);
+	if (err)
+		return err;
+
+	return 0;
+}
+
+static int mchp23k256_remove(struct spi_device *spi)
+{
+	struct mchp23k256_flash *flash = spi_get_drvdata(spi);
+
+	return mtd_device_unregister(&flash->mtd);
+}
+
+static struct spi_driver mchp23k256_driver = {
+	.driver = {
+		.name	= "mchp23k256",
+	},
+	.probe		= mchp23k256_probe,
+	.remove		= mchp23k256_remove,
+};
+
+module_spi_driver(mchp23k256_driver);
+
+MODULE_DESCRIPTION("MTD SPI driver for MCHP23K256 RAM chips");
+MODULE_AUTHOR("Andrew Lunn <[e-mail]>");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("spi:mchp23k256");