mtd: physmap_of: add a hook for Intel IXP4xx flash probing

In order to support device tree probing of IXP4xx NOR flash
chips, a certain big-endian or mixed-endian memory access
pattern need to be used.

I have opted to use the pattern set by previous plug-ins
to physmap for Gemini and Versatile, just override some
functions and reuse most of the physmap core code as it
is to minimize maintenance.

Parts of drivers/mtd/ixp4xx.c are copied into this file.

After we have IXP4xx converted fully to device tree, the
drivers/mtd/ixp4xx.c file will be deleted and this will
be the only access pattern to the IXP4xx flash.

I did not keep the quirk in the flash write function
after probe, where the old code for a while checks for
access to odd addresses, fails and assigns a "faster"
write function once it has convinced probe to only use
2-byte accesses. As we mandate that this device should
be using bank-width = <2> this should not be a problem
unless misconfigured.

Signed-off-by: Linus Walleij <[e-mail]>
Signed-off-by: Miquel Raynal <[e-mail]>

drivers/mtd/maps/Kconfig

···
 	  platforms, some detection and setting up parallel mode on the
 	  external interface.
 
+config MTD_PHYSMAP_IXP4XX
+	bool "Intel IXP4xx OF-based physical memory map handling"
+	depends on MTD_PHYSMAP_OF
+	depends on ARM
+	select MTD_COMPLEX_MAPPINGS
+	select MTD_CFI_BE_BYTE_SWAP if CPU_BIG_ENDIAN
+	default ARCH_IXP4XX
+	help
+	  This provides some extra DT physmap parsing for the Intel IXP4xx
+	  platforms, some elaborate endianness handling in particular.
+
 config MTD_PHYSMAP_GPIO_ADDR
 	bool "GPIO-assisted Flash Chip Support"
 	depends on MTD_PHYSMAP

drivers/mtd/maps/Makefile

···
 physmap-objs-y			+= physmap-core.o
 physmap-objs-$(CONFIG_MTD_PHYSMAP_VERSATILE) += physmap-versatile.o
 physmap-objs-$(CONFIG_MTD_PHYSMAP_GEMINI) += physmap-gemini.o
+physmap-objs-$(CONFIG_MTD_PHYSMAP_IXP4XX) += physmap-ixp4xx.o
 physmap-objs			:= $(physmap-objs-y)
 obj-$(CONFIG_MTD_PHYSMAP)	+= physmap.o
 obj-$(CONFIG_MTD_PISMO)		+= pismo.o

drivers/mtd/maps/physmap-core.c

···
 #include <linux/gpio/consumer.h>
 
 #include "physmap-gemini.h"
+#include "physmap-ixp4xx.h"
 #include "physmap-versatile.h"
 
 struct physmap_flash_info {
···
 		info->maps[i].device_node = dp;
 
 		err = of_flash_probe_gemini(dev, dp, &info->maps[i]);
+		if (err)
+			return err;
+
+		err = of_flash_probe_ixp4xx(dev, dp, &info->maps[i]);
 		if (err)
 			return err;
 

drivers/mtd/maps/physmap-ixp4xx.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Intel IXP4xx OF physmap add-on
+ * Copyright (C) 2019 Linus Walleij <[e-mail]>
+ *
+ * Based on the ixp4xx.c map driver, originally written by:
+ * Intel Corporation
+ * Deepak Saxena <[e-mail]>
+ * Copyright (C) 2002 Intel Corporation
+ * Copyright (C) 2003-2004 MontaVista Software, Inc.
+ */
+#include <linux/export.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/mtd/map.h>
+#include <linux/mtd/xip.h>
+#include "physmap-ixp4xx.h"
+
+/*
+ * Read/write a 16 bit word from flash address 'addr'.
+ *
+ * When the cpu is in little-endian mode it swizzles the address lines
+ * ('address coherency') so we need to undo the swizzling to ensure commands
+ * and the like end up on the correct flash address.
+ *
+ * To further complicate matters, due to the way the expansion bus controller
+ * handles 32 bit reads, the byte stream ABCD is stored on the flash as:
+ *     D15    D0
+ *     +---+---+
+ *     | A | B | 0
+ *     +---+---+
+ *     | C | D | 2
+ *     +---+---+
+ * This means that on LE systems each 16 bit word must be swapped. Note that
+ * this requires CONFIG_MTD_CFI_BE_BYTE_SWAP to be enabled to 'unswap' the CFI
+ * data and other flash commands which are always in D7-D0.
+ */
+#ifndef CONFIG_CPU_BIG_ENDIAN
+
+static inline u16 flash_read16(void __iomem *addr)
+{
+	return be16_to_cpu(__raw_readw((void __iomem *)((unsigned long)addr ^ 0x2)));
+}
+
+static inline void flash_write16(u16 d, void __iomem *addr)
+{
+	__raw_writew(cpu_to_be16(d), (void __iomem *)((unsigned long)addr ^ 0x2));
+}
+
+#define	BYTE0(h)	((h) & 0xFF)
+#define	BYTE1(h)	(((h) >> 8) & 0xFF)
+
+#else
+
+static inline u16 flash_read16(const void __iomem *addr)
+{
+	return __raw_readw(addr);
+}
+
+static inline void flash_write16(u16 d, void __iomem *addr)
+{
+	__raw_writew(d, addr);
+}
+
+#define	BYTE0(h)	(((h) >> 8) & 0xFF)
+#define	BYTE1(h)	((h) & 0xFF)
+#endif
+
+static map_word ixp4xx_read16(struct map_info *map, unsigned long ofs)
+{
+	map_word val;
+
+	val.x[0] = flash_read16(map->virt + ofs);
+	return val;
+}
+
+/*
+ * The IXP4xx expansion bus only allows 16-bit wide acceses
+ * when attached to a 16-bit wide device (such as the 28F128J3A),
+ * so we can't just memcpy_fromio().
+ */
+static void ixp4xx_copy_from(struct map_info *map, void *to,
+			     unsigned long from, ssize_t len)
+{
+	u8 *dest = (u8 *) to;
+	void __iomem *src = map->virt + from;
+
+	if (len <= 0)
+		return;
+
+	if (from & 1) {
+		*dest++ = BYTE1(flash_read16(src-1));
+		src++;
+		--len;
+	}
+
+	while (len >= 2) {
+		u16 data = flash_read16(src);
+		*dest++ = BYTE0(data);
+		*dest++ = BYTE1(data);
+		src += 2;
+		len -= 2;
+	}
+
+	if (len > 0)
+		*dest++ = BYTE0(flash_read16(src));
+}
+
+static void ixp4xx_write16(struct map_info *map, map_word d, unsigned long adr)
+{
+	flash_write16(d.x[0], map->virt + adr);
+}
+
+int of_flash_probe_ixp4xx(struct platform_device *pdev,
+			  struct device_node *np,
+			  struct map_info *map)
+{
+	struct device *dev = &pdev->dev;
+
+	/* Multiplatform guard */
+	if (!of_device_is_compatible(np, "intel,ixp4xx-flash"))
+		return 0;
+
+	map->read = ixp4xx_read16;
+	map->write = ixp4xx_write16;
+	map->copy_from = ixp4xx_copy_from;
+	map->copy_to = NULL;
+
+	dev_info(dev, "initialized Intel IXP4xx-specific physmap control\n");
+
+	return 0;
+}

drivers/mtd/maps/physmap-ixp4xx.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/of.h>
+#include <linux/mtd/map.h>
+
+#ifdef CONFIG_MTD_PHYSMAP_IXP4XX
+int of_flash_probe_ixp4xx(struct platform_device *pdev,
+			  struct device_node *np,
+			  struct map_info *map);
+#else
+static inline
+int of_flash_probe_ixp4xx(struct platform_device *pdev,
+			  struct device_node *np,
+			  struct map_info *map)
+{
+	return 0;
+}
+#endif