linux-kernel - Re: [PATCH] regmap: fix writes to non incrementing registers

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Message-ID: <20190814100115.GF4640@sirena.co.uk>
Date:   Wed, 14 Aug 2019 11:01:15 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Ben Whitten <ben.whitten@...il.com>
Cc:     linux-kernel@...r.kernel.org, afaerber@...e.de,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH] regmap: fix writes to non incrementing registers

On Tue, Aug 13, 2019 at 10:22:51PM +0100, Ben Whitten wrote:

> @@ -1489,10 +1489,11 @@ static int _regmap_raw_write_impl(struct regmap *map, unsigned int reg,
>  	WARN_ON(!map->bus);
>  
>  	/* Check for unwritable registers before we start */
> -	for (i = 0; i < val_len / map->format.val_bytes; i++)
> -		if (!regmap_writeable(map,
> -				     reg + regmap_get_offset(map, i)))
> -			return -EINVAL;
> +	if (!regmap_writeable_noinc(map, reg))
> +		for (i = 0; i < val_len / map->format.val_bytes; i++)
> +			if (!regmap_writeable(map,
> +					     reg + regmap_get_offset(map, i)))
> +				return -EINVAL;

This feels like we're getting ourselves confused about nonincrementing
registers and probably have other breakage somewhere else - we're
already checking for nonincrementability in regmap_write_noinc(), and
here we're only checking if the first register in the block has that
property which might blow up on us if there's a register in the middle
of the block that is nonincrementable.  If we're going to check this
here I think we should check on every register, but this is
_raw_write_impl() which is part of the call path for implementing
regmap_noinc_write() so checking here will break the API purpose
designed for nonincrementing writes.

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