linux-kernel - Re: [PATCH 1/2] regmap: Support half writes and padding between register and value.

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Message-ID: <20110908162715.GB3098@opensource.wolfsonmicro.com>
Date:	Thu, 8 Sep 2011 09:27:15 -0700
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Jonathan Cameron <jic23@....ac.uk>
Cc:	linux-kernel@...r.kernel.org, Michael.Hennerich@...log.com,
	linux-iio@...r.kernel.org
Subject: Re: [PATCH 1/2] regmap: Support half writes and padding between
 register and value.

On Thu, Sep 08, 2011 at 03:09:23PM +0100, Jonathan Cameron wrote:

> Note half writes currently assume address numbers are even only.
> That's a pain for caching so other suggestions welcome.  I could set
> it as a 7 bit address and increase the padding to 9 bits.  That makes
> the write bit a little strange though as it will be going into the
> padding.

This needs more documentation somewhere explaining what a half write is
and/or a better name for half write but doesn't look too invasive so I
think this approach can work.  If we come up with something better later
then we can always change things, there shouldn't be too many users to
update if that happens.

> -	map->format.reg_bytes = config->reg_bits / 8;
> +	map->format.buf_size = (config->reg_bits +
> +				config->reg_pad_bits +
> +				config->val_bits) / 8;
> +	map->format.reg_bytes = (config->reg_bits + config->reg_pad_bits)/ 8;

Please do a patch adding padding separately - that does seem like a
useful thing to have in general, with the option of having it both
before and after the register.

> -	if (val == map->work_buf + map->format.reg_bytes)
> -		ret = map->bus->write(map->dev, map->work_buf,
> -				      map->format.reg_bytes + val_len);
> -	else if (map->bus->gather_write)
> +	if (val == map->work_buf + map->format.reg_bytes) {
> +		if (map->format.half_write) {
> +			ret = map->bus->write(map->dev, map->work_buf,
> +					      (map->format.reg_bytes +
> +					       val_len) >> 1);
> +			if (ret >= 0)
> +				ret = map->bus->write(map->dev,
> +						      map->work_buf +
> +						      ((map->format.reg_bytes +
> +							val_len) >> 1),
> +						      (map->format.reg_bytes +
> +						       val_len) >> 1);
> +		} else {
> +			ret = map->bus->write(map->dev, map->work_buf,
> +					      map->format.reg_bytes + val_len);
> +		}

This code is getting very complicated...  I think it'd be clearer to
have a special case at the head of the function that does the half write
stuff.  It also feels like the half bit needs parameterisation, but I
can't immediately think of how to do that sensibly.
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