Date:	Mon, 05 Sep 2011 18:14:38 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Dimitris Papastamos <dp@...nsource.wolfsonmicro.com>
CC:	linux-kernel@...r.kernel.org,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Liam Girdwood <lrg@...com>,
	Graeme Gregory <gg@...mlogic.co.uk>,
	Samuel Oritz <sameo@...ux.intel.com>
Subject: Re: [PATCH 1/6] regmap: Introduce caching support

On 09/05/2011 03:50 PM, Dimitris Papastamos wrote:
> This patch introduces caching support for regmap.  The regcache API
> has evolved essentially out of ASoC soc-cache so most of the actual
> caching types (except LZO) have been tested in the past.
> 
> The purpose of regcache is to optimize in time and space the handling
> of register caches.  Time optimization is achieved by not having to go
> over a slow bus like I2C to read the value of a register, instead it is
> cached locally in memory and can be retrieved faster.  Regarding space
> optimization, some of the cache types are better at packing the caches,
> for e.g. the rbtree and the LZO caches.  By doing this the sacrifice in
> time still wins over doing I2C transactions.
> 
> Signed-off-by: Dimitris Papastamos <dp@...nsource.wolfsonmicro.com>

I gave it a try with the rbtree caching on real hardware and noticed some
smaller issues, but with those fixed it seems to work fine.

> ---
>  drivers/base/regmap/Makefile   |    2 +-
>  drivers/base/regmap/internal.h |   52 +++++++
>  drivers/base/regmap/regcache.c |  302 ++++++++++++++++++++++++++++++++++++++++
>  include/linux/regmap.h         |   24 +++-
>  4 files changed, 374 insertions(+), 6 deletions(-)
>  create mode 100644 drivers/base/regmap/regcache.c
> 
> diff --git a/drivers/base/regmap/Makefile b/drivers/base/regmap/Makefile
> index 057c13f..2e103ea 100644
> --- a/drivers/base/regmap/Makefile
> +++ b/drivers/base/regmap/Makefile
> @@ -1,4 +1,4 @@
> -obj-$(CONFIG_REGMAP) += regmap.o
> +obj-$(CONFIG_REGMAP) += regmap.o regcache.o
>  obj-$(CONFIG_DEBUG_FS) += regmap-debugfs.o
>  obj-$(CONFIG_REGMAP_I2C) += regmap-i2c.o
>  obj-$(CONFIG_REGMAP_SPI) += regmap-spi.o
> diff --git a/drivers/base/regmap/internal.h b/drivers/base/regmap/internal.h
> index 5ab3fef..dbeccd2 100644
> --- a/drivers/base/regmap/internal.h
> +++ b/drivers/base/regmap/internal.h
> @@ -17,6 +17,7 @@
>  #include <linux/fs.h>
>  
>  struct regmap;
> +struct regcache_ops;
>  
>  struct regmap_format {
>  	size_t buf_size;
> @@ -46,6 +47,40 @@ struct regmap {
>  	bool (*readable_reg)(struct device *dev, unsigned int reg);
>  	bool (*volatile_reg)(struct device *dev, unsigned int reg);
>  	bool (*precious_reg)(struct device *dev, unsigned int reg);
> +
> +	/* regcache specific members */
> +	const struct regcache_ops *cache_ops;
> +	enum regcache_type cache_type;
> +
> +	/* number of bytes in cache_defaults_raw */
> +	unsigned int cache_size_raw;
> +	/* number of bytes per word in cache_defaults_raw */
> +	unsigned int cache_word_size;
> +	/* number of entries in cache_defaults */
> +	unsigned int num_cache_defaults;
> +	/* number of entries in cache_defaults_raw */
> +	unsigned int num_cache_defaults_raw;
> +
> +	/* if set, only the cache is modified not the HW */
> +	unsigned int cache_only:1;
> +	/* if set, only the HW is modified not the cache */
> +	unsigned int cache_bypass:1;
> +	/* if set, remember to free cache_defaults_raw */
> +	unsigned int cache_free:1;
> +
> +	struct reg_default *cache_defaults;
> +	const void *cache_defaults_raw;
> +	void *cache;
> +};
> +
> +struct regcache_ops {
> +	const char *name;
> +	enum regcache_type type;
> +	int (*init)(struct regmap *map);
> +	int (*exit)(struct regmap *map);
> +	int (*read)(struct regmap *map, unsigned int reg, unsigned int *value);
> +	int (*write)(struct regmap *map, unsigned int reg, unsigned int value);
> +	int (*sync)(struct regmap *map);
>  };
>  
>  bool regmap_writeable(struct regmap *map, unsigned int reg);
> @@ -63,4 +98,21 @@ void regmap_debugfs_init(struct regmap *map) { }
>  void regmap_debugfs_exit(struct regmap *map) { }
>  #endif
>  
> +/* regcache core declarations */
> +int regcache_init(struct regmap *map);
> +void regcache_exit(struct regmap *map);
> +int regcache_read(struct regmap *map,
> +		       unsigned int reg, unsigned int *value);
> +int regcache_write(struct regmap *map,
> +			unsigned int reg, unsigned int value);
> +int regcache_sync(struct regmap *map);
> +
> +unsigned int regcache_get_val(const void *base, unsigned int idx,
> +			      unsigned int word_size);
> +bool regcache_set_val(void *base, unsigned int idx,
> +		      unsigned int val, unsigned int word_size);
> +int regcache_lookup_reg(struct regmap *map, unsigned int reg);
> +int regcache_insert_reg(struct regmap *map, unsigned int reg,
> +			unsigned int val);
> +
>  #endif
> diff --git a/drivers/base/regmap/regcache.c b/drivers/base/regmap/regcache.c
> new file mode 100644
> index 0000000..f26df00
> --- /dev/null
> +++ b/drivers/base/regmap/regcache.c
> @@ -0,0 +1,302 @@
> +/*
> + * Register cache access API
> + *
> + * Copyright 2011 Wolfson Microelectronics plc
> + *
> + * Author: Dimitris Papastamos <dp@...nsource.wolfsonmicro.com>
> + *
> + * This program 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/slab.h>
> +#include <trace/events/regmap.h>
> +
> +#include "internal.h"
> +
> +static const struct regcache_ops *cache_types[] = {
> +};
> +
> +int regcache_init(struct regmap *map)
> +{
> +	int i, j;
> +	int count;
> +	int ret;
> +	unsigned int val;
> +	void *tmp_buf;
> +
> +	if (map->cache_type == REGCACHE_NONE)
> +		return 0;
> +
> +	for (i = 0; i < ARRAY_SIZE(cache_types); i++)
> +		if (cache_types[i]->type == map->cache_type)
> +			break;
> +
> +	if (i == ARRAY_SIZE(cache_types)) {
> +		dev_err(map->dev, "Could not match compress type: %d\n",
> +			map->cache_type);
> +		return -EINVAL;
> +	}
> +
> +	map->cache = NULL;
> +	map->cache_ops = cache_types[i];
> +
> +	if (!map->cache_ops->read ||
> +	    !map->cache_ops->write ||
> +	    !map->cache_ops->name)
> +		return -EINVAL;
> +
> +	/* We still need to ensure that the cache_defaults
> +	 * won't vanish from under us.  We'll need to make
> +	 * a copy of it.
> +	 */
> +	if (map->cache_defaults) {
> +		if (!map->num_cache_defaults)
> +			return -EINVAL;
> +		tmp_buf = kmemdup(map->cache_defaults, map->num_cache_defaults *
> +				  sizeof(struct reg_default), GFP_KERNEL);
> +		if (!tmp_buf)
> +			return -ENOMEM;
> +		map->cache_defaults = tmp_buf;
> +		goto cache_init;
> +	}

Maybe put the cache initialization from raw cache into a separate function and
don't use goto. Should keep things a bit more readable.

> +	/* Some devices such as PMIC's don't have cache defaults,
> +	 * we cope with this by reading back the HW registers and
> +	 * crafting the cache defaults by hand.
> +	 */
> +	if (!map->cache_defaults_raw) {
> +		if (!map->num_cache_defaults_raw)
> +			return -EINVAL;
> +		dev_warn(map->dev, "No cache defaults, reading back from HW\n");
> +		tmp_buf = kmalloc(map->cache_size_raw, GFP_KERNEL);
> +		if (!tmp_buf)
> +			return -EINVAL;
> +		ret = regmap_bulk_read(map, 0, tmp_buf,
> +				       map->num_cache_defaults_raw);
> +		if (ret < 0) {
> +			kfree(tmp_buf);
> +			return ret;
> +		}
> +		map->cache_defaults_raw = tmp_buf;
> +		map->cache_free = 1;
> +	}
> +
> +	/* calculate the size of cache_defaults */
> +	for (count = 0, i = 0; i < map->num_cache_defaults_raw; i++) {
> +		val = regcache_get_val(map->cache_defaults_raw,
> +				       i, map->cache_word_size);
> +		if (!val)
> +			continue;
> +		count++;
> +	}
> +
> +	map->cache_defaults = kmalloc(count * sizeof(struct reg_default),
> +				      GFP_KERNEL);
> +	if (!map->cache_defaults)
> +		return -ENOMEM;
> +
> +	/* fill the cache_defaults */
> +	map->num_cache_defaults = count;
> +	for (i = 0, j = 0; i < map->num_cache_defaults_raw; i++) {
> +		val = regcache_get_val(map->cache_defaults_raw,
> +				       i, map->cache_word_size);
> +		if (!val)
> +			continue;
> +		map->cache_defaults[j].reg = i;
> +		map->cache_defaults[j].def = val;
> +		j++;
> +	}
> +
> +cache_init:
> +	if (map->cache_ops->init) {
> +		dev_dbg(map->dev, "Initializing %s cache\n",
> +			map->cache_ops->name);
> +		return map->cache_ops->init(map);
> +	}
> +	return 0;
> +}
> +
> [...]
> +
> +/**
> + * regcache_read: Fetch the value of a given register from the cache.
> + *
> + * @map: map to configure.
> + * @reg: The register index.
> + * @value: The value to be returned.
> + *
> + * Return a negative value on failure, 0 on success.
> + */
> +int regcache_read(struct regmap *map,
> +		  unsigned int reg, unsigned int *value)
> +{
> +	unsigned int max_reg;
> +
> +	if (map->cache_type == REGCACHE_NONE)
> +		return 0;
> +
> +	BUG_ON(!map->cache_ops);
> +
> +	if (!regmap_readable(map, reg))
> +		return 0;

Shouldn't we return some kind of error here? Otherwise value we indicate
success, but *value contain random garbage.

> +
> +	if (map->max_register)
> +		max_reg = map->max_register;
> +	else
> +		max_reg = map->num_cache_defaults_raw;
> +
> +
> +	if (reg < max_reg && !regmap_volatile(map, reg))
> +		return map->cache_ops->read(map, reg, value);
> +	return -EINVAL;
> +}
> +EXPORT_SYMBOL_GPL(regcache_read);
> +
> +/**
> + * regcache_write: Set the value of a given register in the cache.
> + *
> + * @map: map to configure.
> + * @reg: The register index.
> + * @value: The new register value.
> + *
> + * Return a negative value on failure, 0 on success.
> + */
> +int regcache_write(struct regmap *map,
> +		   unsigned int reg, unsigned int value)
> +{
> +	unsigned int max_reg;
> +
> +	if (map->cache_type == REGCACHE_NONE)
> +		return 0;
> +
> +	BUG_ON(!map->cache_ops);
> +
> +	if (!regmap_writeable(map, reg))
> +		return 0;

Same here.

> +
> +	if (map->max_register)
> +		max_reg = map->max_register;
> +	else
> +		max_reg = map->num_cache_defaults_raw;
> +
> +	if (reg < max_reg && !regmap_volatile(map, reg))
> +		return map->cache_ops->write(map, reg, value);
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(regcache_write);
> +
> [...]
> diff --git a/include/linux/regmap.h b/include/linux/regmap.h
> index 449e264..7591e01 100644
> --- a/include/linux/regmap.h
> +++ b/include/linux/regmap.h
> @@ -20,6 +20,11 @@
>  struct i2c_client;
>  struct spi_device;
>  
> +/* An enum of all the supported cache types */
> +enum regcache_type {
> +	REGCACHE_NONE,
> +};
> +
>  /**
>   * Default value for a register.  We use an array of structs rather
>   * than a simple array as many modern devices have very sparse
> @@ -50,9 +55,14 @@ struct reg_default {
>   *                (eg, a clear on read interrupt status register).
>   *
>   * @max_register: Optional, specifies the maximum valid register index.
> - * @reg_defaults: Power on reset values for registers (for use with
> - *                register cache support).
> - * @num_reg_defaults: Number of elements in reg_defaults.
> + *
> + * @cache_type: The actual cache type.
> + * @cache_defaults: Power on reset values for registers (for use with
> + *                  register cache support).
> + * @num_cache_defaults: Number of elements in cache_defaults.
> + * @cache_defaults_raw: Power on reset values for registers (for use with
> + *                 register cache support).
> + * @num_cache_defaults_raw: Number of elements in cache_defaults_raw.
>   */
>  struct regmap_config {
>  	int reg_bits;
> @@ -64,8 +74,12 @@ struct regmap_config {
>  	bool (*precious_reg)(struct device *dev, unsigned int reg);
>  
>  	unsigned int max_register;
> -	struct reg_default *reg_defaults;
> -	int num_reg_defaults;
> +
> +	enum regcache_type cache_type;
> +	struct reg_default *cache_defaults;

Should be made const.

> +	unsigned int num_cache_defaults;
> +	const void *cache_defaults_raw;
> +	unsigned int num_cache_defaults_raw;
>  };
--
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