regmap: Add RAM backed register map

Add a register map that is a simple array of memory, for use in
KUnit testing of the framework. This is not exposed in regmap.h
since I can't think of a non-test use case, it is purely for use
internally. To facilitate testing we track if registers have been
read or written to.
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230324-regmap-kunit-v2-1-b208801dc2c8@kernel.org

drivers/base/regmap/Kconfig

@@ -41,6 +41,9 @@ config REGMAP_MMIO
 config REGMAP_IRQ
 	bool
 
+config REGMAP_RAM
+	tristate
+
 config REGMAP_SOUNDWIRE
 	tristate
 	depends on SOUNDWIRE

drivers/base/regmap/Makefile

@@ -7,6 +7,7 @@ obj-$(CONFIG_REGMAP) += regcache-rbtree.o regcache-flat.o
 obj-$(CONFIG_DEBUG_FS) += regmap-debugfs.o
 obj-$(CONFIG_REGMAP_AC97) += regmap-ac97.o
 obj-$(CONFIG_REGMAP_I2C) += regmap-i2c.o
+obj-$(CONFIG_REGMAP_RAM) += regmap-ram.o
 obj-$(CONFIG_REGMAP_SLIMBUS) += regmap-slimbus.o
 obj-$(CONFIG_REGMAP_SPI) += regmap-spi.o
 obj-$(CONFIG_REGMAP_SPMI) += regmap-spmi.o

drivers/base/regmap/internal.h

@@ -306,4 +306,23 @@ static inline unsigned int regcache_get_index_by_order(const struct regmap *map,
 	return reg >> map->reg_stride_order;
 }
 
+struct regmap_ram_data {
+	unsigned int *vals;  /* Allocatd by caller */
+	bool *read;
+	bool *written;
+};
+
+/*
+ * Create a test register map with data stored in RAM, not intended
+ * for practical use.
+ */
+struct regmap *__regmap_init_ram(const struct regmap_config *config,
+				 struct regmap_ram_data *data,
+				 struct lock_class_key *lock_key,
+				 const char *lock_name);
+
+#define regmap_init_ram(config, data)					\
+	__regmap_lockdep_wrapper(__regmap_init_ram, #config, config, data)
+
+
 #endif

drivers/base/regmap/regmap-ram.c

+// SPDX-License-Identifier: GPL-2.0
+//
+// Register map access API - Memory region
+//
+// This is intended for testing only
+//
+// Copyright (c) 2023, Arm Ltd
+
+#include <linux/clk.h>
+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/regmap.h>
+#include <linux/slab.h>
+#include <linux/swab.h>
+
+#include "internal.h"
+
+static int regmap_ram_write(void *context, unsigned int reg, unsigned int val)
+{
+	struct regmap_ram_data *data = context;
+
+	data->vals[reg] = val;
+	data->written[reg] = true;
+
+	return 0;
+}
+
+static int regmap_ram_read(void *context, unsigned int reg, unsigned int *val)
+{
+	struct regmap_ram_data *data = context;
+
+	*val = data->vals[reg];
+	data->read[reg] = true;
+
+	return 0;
+}
+
+static void regmap_ram_free_context(void *context)
+{
+	struct regmap_ram_data *data = context;
+
+	kfree(data->vals);
+	kfree(data->read);
+	kfree(data->written);
+	kfree(data);
+}
+
+static const struct regmap_bus regmap_ram = {
+	.fast_io = true,
+	.reg_write = regmap_ram_write,
+	.reg_read = regmap_ram_read,
+	.free_context = regmap_ram_free_context,
+};
+
+struct regmap *__regmap_init_ram(const struct regmap_config *config,
+				 struct regmap_ram_data *data,
+				 struct lock_class_key *lock_key,
+				 const char *lock_name)
+{
+	struct regmap *map;
+
+	if (!config->max_register) {
+		pr_crit("No max_register specified for RAM regmap\n");
+		return ERR_PTR(-EINVAL);
+	}
+
+	data->read = kcalloc(sizeof(bool), config->max_register + 1,
+			     GFP_KERNEL);
+	if (!data->read)
+		return ERR_PTR(-ENOMEM);
+
+	data->written = kcalloc(sizeof(bool), config->max_register + 1,
+				GFP_KERNEL);
+	if (!data->written)
+		return ERR_PTR(-ENOMEM);
+
+	map = __regmap_init(NULL, &regmap_ram, data, config,
+			    lock_key, lock_name);
+
+	return map;
+}
+EXPORT_SYMBOL_GPL(__regmap_init_ram);
+
+MODULE_LICENSE("GPL v2");