[v3] mtd: physmap: Add Baikal-T1 physically mapped ROM support

diff --git a/drivers/mtd/maps/Kconfig b/drivers/mtd/maps/Kconfig
index fd37553f1b07..6650acbc961e 100644
--- a/drivers/mtd/maps/Kconfig
+++ b/drivers/mtd/maps/Kconfig
@@ -75,6 +75,17 @@  config MTD_PHYSMAP_OF
 	  physically into the CPU's memory. The mapping description here is
 	  taken from OF device tree.
 
+config MTD_PHYSMAP_BT1_ROM
+	bool "Baikal-T1 Boot ROMs OF-based physical memory map handling"
+	depends on MTD_PHYSMAP_OF
+	depends on MIPS_BAIKAL_T1 || COMPILE_TEST
+	select MTD_COMPLEX_MAPPINGS
+	select MULTIPLEXER
+	select MUX_MMIO
+	help
+	  This provides some extra DT physmap parsing for the Baikal-T1
+	  platforms, some detection and setting up ROMs-specific accessors.
+
 config MTD_PHYSMAP_VERSATILE
 	bool "ARM Versatile OF-based physical memory map handling"
 	depends on MTD_PHYSMAP_OF
diff --git a/drivers/mtd/maps/Makefile b/drivers/mtd/maps/Makefile
index c0da86a5d26f..79f018cf412f 100644
--- a/drivers/mtd/maps/Makefile
+++ b/drivers/mtd/maps/Makefile
@@ -18,6 +18,7 @@  obj-$(CONFIG_MTD_CK804XROM)	+= ck804xrom.o
 obj-$(CONFIG_MTD_TSUNAMI)	+= tsunami_flash.o
 obj-$(CONFIG_MTD_PXA2XX)	+= pxa2xx-flash.o
 physmap-objs-y			+= physmap-core.o
+physmap-objs-$(CONFIG_MTD_PHYSMAP_BT1_ROM) += physmap-bt1-rom.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
diff --git a/drivers/mtd/maps/physmap-bt1-rom.c b/drivers/mtd/maps/physmap-bt1-rom.c
new file mode 100644
index 000000000000..27cfe1c63a2e
--- /dev/null
+++ b/drivers/mtd/maps/physmap-bt1-rom.c
@@ -0,0 +1,126 @@ 
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2020 BAIKAL ELECTRONICS, JSC
+ *
+ * Authors:
+ *   Serge Semin <Sergey.Semin@baikalelectronics.ru>
+ *
+ * Baikal-T1 Physically Mapped Internal ROM driver
+ */
+#include <linux/bits.h>
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/mtd/map.h>
+#include <linux/mtd/xip.h>
+#include <linux/mux/consumer.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/platform_device.h>
+#include <linux/string.h>
+#include <linux/types.h>
+
+#include "physmap-bt1-rom.h"
+
+/*
+ * Baikal-T1 SoC ROMs are only accessible by the dword-aligned instructions.
+ * We have to take this into account when implementing the data read-methods.
+ * Note there is no need in bothering with endianness, since both Baikal-T1
+ * CPU and MMIO are LE.
+ */
+static map_word __xipram bt1_rom_map_read(struct map_info *map,
+					  unsigned long ofs)
+{
+	void __iomem *src = map->virt + ofs;
+	unsigned long shift;
+	map_word ret;
+	u32 data;
+
+	/* Read data within offset dword. */
+	shift = (unsigned long)src & 0x3;
+	data = readl_relaxed(src - shift);
+	if (!shift) {
+		ret.x[0] = data;
+		return ret;
+	}
+	ret.x[0] = data >> (shift * BITS_PER_BYTE);
+
+	/* Read data from the next dword. */
+	shift = 4 - shift;
+	if (ofs + shift >= map->size)
+		return ret;
+
+	data = readl_relaxed(src + shift);
+	ret.x[0] |= data << (shift * BITS_PER_BYTE);
+
+	return ret;
+}
+
+static void __xipram bt1_rom_map_copy_from(struct map_info *map,
+					   void *to, unsigned long from,
+					   ssize_t len)
+{
+	void __iomem *src = map->virt + from;
+	ssize_t shift, chunk;
+	u32 data;
+
+	if (len <= 0 || from >= map->size)
+		return;
+
+	/* Make sure we don't go over the map limit. */
+	len = min_t(ssize_t, map->size - from, len);
+
+	/*
+	 * Since requested data size can be pretty big we have to implement
+	 * the copy procedure as optimal as possible. That's why it's split
+	 * up into the next three stages: unaligned head, aligned body,
+	 * unaligned tail.
+	 */
+	shift = (ssize_t)src & 0x3;
+	if (shift) {
+		chunk = min_t(ssize_t, 4 - shift, len);
+		data = readl_relaxed(src - shift);
+		memcpy(to, &data + shift, chunk);
+		src += chunk;
+		to += chunk;
+		len -= chunk;
+	}
+
+	while (len >= 4) {
+		data = readl_relaxed(src);
+		memcpy(to, &data, 4);
+		src += 4;
+		to += 4;
+		len -= 4;
+	}
+
+	if (len) {
+		data = readl_relaxed(src);
+		memcpy(to, &data, len);
+	}
+}
+
+int of_flash_probe_bt1_rom(struct platform_device *pdev,
+			   struct device_node *np,
+			   struct map_info *map)
+{
+	struct device *dev = &pdev->dev;
+
+	/* It's supposed to be read-only MTD. */
+	if (!of_device_is_compatible(np, "mtd-rom")) {
+		dev_info(dev, "No mtd-rom compatible string\n");
+		return 0;
+	}
+
+	/* Multiplatform guard. */
+	if (!of_device_is_compatible(np, "baikal,bt1-int-rom"))
+		return 0;
+
+	/* Sanity check the device parameters retrieved from DTB. */
+	if (map->bankwidth != 4)
+		dev_warn(dev, "Bank width is supposed to be 32 bits wide\n");
+
+	map->read = bt1_rom_map_read;
+	map->copy_from = bt1_rom_map_copy_from;
+
+	return 0;
+}
diff --git a/drivers/mtd/maps/physmap-bt1-rom.h b/drivers/mtd/maps/physmap-bt1-rom.h
new file mode 100644
index 000000000000..6782899598a4
--- /dev/null
+++ b/drivers/mtd/maps/physmap-bt1-rom.h
@@ -0,0 +1,17 @@ 
+/* SPDX-License-Identifier: GPL-2.0-only */
+#include <linux/mtd/map.h>
+#include <linux/of.h>
+
+#ifdef CONFIG_MTD_PHYSMAP_BT1_ROM
+int of_flash_probe_bt1_rom(struct platform_device *pdev,
+			   struct device_node *np,
+			   struct map_info *map);
+#else
+static inline
+int of_flash_probe_bt1_rom(struct platform_device *pdev,
+			   struct device_node *np,
+			   struct map_info *map)
+{
+	return 0;
+}
+#endif
diff --git a/drivers/mtd/maps/physmap-core.c b/drivers/mtd/maps/physmap-core.c
index 8f7f966fa9a7..8843e780f5c8 100644
--- a/drivers/mtd/maps/physmap-core.c
+++ b/drivers/mtd/maps/physmap-core.c
@@ -41,6 +41,7 @@ 
 #include <linux/pm_runtime.h>
 #include <linux/gpio/consumer.h>
 
+#include "physmap-bt1-rom.h"
 #include "physmap-gemini.h"
 #include "physmap-ixp4xx.h"
 #include "physmap-versatile.h"
@@ -371,6 +372,10 @@  static int physmap_flash_of_init(struct platform_device *dev)
 		info->maps[i].bankwidth = bankwidth;
 		info->maps[i].device_node = dp;
 
+		err = of_flash_probe_bt1_rom(dev, dp, &info->maps[i]);
+		if (err)
+			return err;
+
 		err = of_flash_probe_gemini(dev, dp, &info->maps[i]);
 		if (err)
 			return err;