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

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Date:   Wed, 14 Aug 2019 15:32:37 +0200
From:   Andreas Färber <afaerber@...e.de>
To:     Ben Whitten <ben.whitten@...il.com>
Cc:     Mark Brown <broonie@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>, nandor.han@...sala.com
Subject: Re: [PATCH] regmap: fix writes to non incrementing registers

Am 14.08.19 um 15:09 schrieb Ben Whitten:
> On Wed, 14 Aug 2019 at 11:01, Mark Brown <broonie@...nel.org> wrote:
>>
>> 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.
> 
> So it appeared that the last patch in this area for validating a register
> block [1] broke the regmap_noinc_write use case.

Then please add a Fixes: header to your commit message, so that it gets
backported to all affected upstream and downstream trees.

Thanks,
Andreas

> Because regmap_noinc_write calls _regmap_raw_write and in
> turn hits the _regmap_raw_write_impl, the val_len is the depth of the
> one register to write to and not a block of registers which is assumed
> by the previous check. By inserting a check that the first (and only)
> register is a noinc one allows me to start writing to my FIFO again.
> 
> I'm all for an alternative solution though if there is a cleaner approach.
> 
> Kind regards,
> Ben
> 
> [1] https://lore.kernel.org/patchwork/patch/1057184/
> 


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