linux-kernel - Re: [PATCH 1/4] regmap: Add generic non-memory mapped register access API

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Date:	Mon, 18 Jul 2011 12:38:14 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	Greg KH <greg@...ah.com>, Grant Likely <grant@...retlab.ca>,
	Jean Delvare <khali@...ux-fr.org>,
	Ben Dooks <ben-linux@...ff.org>,
	Dimitris Papastamos <dp@...nsource.wolfsonmicro.com>,
	Liam Girdwood <lrg@...com>,
	Samuel Oritz <sameo@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] regmap: Add generic non-memory mapped register access API

At Mon, 18 Jul 2011 19:07:40 +0900,
Mark Brown wrote:
> 
> +static int _regmap_raw_write(struct regmap *map, unsigned int reg,
> +			     const void *val, size_t val_len)
> +{
> +	void *buf;
> +	int ret = -ENOTSUPP;
> +	size_t len;
> +
> +	map->format.format_reg(map->work_buf, reg);
> +
> +	/* Try to do a gather write if we can */
> +	if (map->bus->gather_write)
> +		ret = map->bus->gather_write(map->dev, map->work_buf,
> +					     map->format.reg_bytes,
> +					     val, val_len);
> +
> +	/* Otherwise fall back on linearising by hand. */
> +	if (ret == -ENOTSUPP) {
> +		len = map->format.reg_bytes + val_len;
> +		buf = kmalloc(len, GFP_KERNEL);
> +		if (!buf)
> +			return -ENOMEM;
> +
> +		memcpy(buf, map->work_buf, map->format.reg_bytes);
> +		memcpy(buf + map->format.reg_bytes, val, val_len);
> +		ret = map->bus->write(map->dev, buf, len);
> +
> +		kfree(buf);

In most cases, val = map->work_buf + map->format.reg_bytes.
How about a bit optimization?

	if (ret == -ENOTSUPP) {
		len = map->format.reg_bytes + val_len;
		if (val == map->work_buf + map->format.reg_bytes)
			ret = map->bus->write(map->dev, map->work_buf, len);
		else {
			buf = kmalloc(len, GFP_KERNEL);
			if (!buf)
				return -ENOMEM;

			memcpy(buf, map->work_buf, map->format.reg_bytes);
			memcpy(buf + map->format.reg_bytes, val, val_len);
			ret = map->bus->write(map->dev, buf, len);

			kfree(buf);
		}
	}


thanks,

Takashi
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