linux-kernel - Re: [PATCH v7 1/7] i2c: add I2C Address Translator (ATR) support

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Date:   Fri, 20 Jan 2023 17:58:30 +0200
From:   Andy Shevchenko <andriy.shevchenko@...el.com>
To:     Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc:     linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Wolfram Sang <wsa@...nel.org>,
        Luca Ceresoli <luca.ceresoli@...tlin.com>,
        Matti Vaittinen <Matti.Vaittinen@...rohmeurope.com>,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Peter Rosin <peda@...ntia.se>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Michael Tretter <m.tretter@...gutronix.de>,
        Shawn Tu <shawnx.tu@...el.com>,
        Hans Verkuil <hverkuil@...all.nl>,
        Mike Pagano <mpagano@...too.org>,
        Krzysztof Hałasa <khalasa@...p.pl>,
        Marek Vasut <marex@...x.de>,
        Luca Ceresoli <luca@...aceresoli.net>
Subject: Re: [PATCH v7 1/7] i2c: add I2C Address Translator (ATR) support

On Thu, Jan 19, 2023 at 12:01:33PM +0200, Tomi Valkeinen wrote:
> On 18/01/2023 16:23, Andy Shevchenko wrote:
> > On Wed, Jan 18, 2023 at 02:40:25PM +0200, Tomi Valkeinen wrote:

...

> > > +	/* Ensure we have enough room to save the original addresses */
> > > +	if (unlikely(chan->orig_addrs_size < num)) {
> > > +		u16 *new_buf;
> > > +
> > > +		new_buf = kmalloc_array(num, sizeof(*new_buf), GFP_KERNEL);
> > 
> > I remember that I asked why we don't use krealloc_array() here... Perhaps
> > that we don't need to copy the old mapping table? Can we put a short comment
> > to clarify this in the code?
> 
> Yes, we don't care about the old data, we just require the buffer to be
> large enough.
> 
> I'm not sure what kind of comment you want here. Isn't this a common idiom,
> where you have a buffer for temporary data, but you might need to resize at
> some point if you need a larger one?

Then why not krealloc_array()? That's the question I want to see the answer for
in the comments:

	/* We don't care about old data, hence no realloc() */

> > > +		if (!new_buf)
> > > +			return -ENOMEM;
> > > +
> > > +		kfree(chan->orig_addrs);
> > > +		chan->orig_addrs = new_buf;
> > > +		chan->orig_addrs_size = num;
> > > +	}

-- 
With Best Regards,
Andy Shevchenko