linux-kernel - Re: [BUG] _regmap_raw_write()

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Message-ID: <ab5b9153-5031-4a54-9966-d0eddd3e76a1@sirena.org.uk>
Date:   Fri, 16 Jun 2023 23:02:51 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Russ Weight <russell.h.weight@...el.com>
Cc:     Jim Wylder <jwylder@...gle.com>,
        "Gerlach, Matthew" <matthew.gerlach@...ux.intel.com>,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [BUG] _regmap_raw_write() - divide-by-zero

On Fri, Jun 16, 2023 at 02:58:24PM -0700, Russ Weight wrote:

> > +     size_t max_data = map->max_raw_write - map->format.reg_bytes -
> > +                     map->format.pad_bytes;

> For the SPI-Avalon implementation, the values used to calculate max_data are:

> regmap->max_raw_write = 4
> regmap->format->reg_bytes = 4
> regmap->format->pad_bytes = 0
> 
> So the above calculation for max_data is: max_data = (4 - 4 - 0) = 0

How does this bus work?  The device can accept a maximum of 4 bytes of
data but the register is 4 bytes in length so there's no space to
transmit a value.

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