linux-kernel - Re: [PATCH] firmware: cirrus: cs_dsp: Avoid padding bytes in cs_dsp_coeff

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Message-ID: <20220425100229.GU38351@ediswmail.ad.cirrus.com>
Date:   Mon, 25 Apr 2022 10:02:29 +0000
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     Richard Fitzgerald <rf@...nsource.cirrus.com>
CC:     <broonie@...nel.org>, <alsa-devel@...a-project.org>,
        <linux-kernel@...r.kernel.org>, <patches@...nsource.cirrus.com>
Subject: Re: [PATCH] firmware: cirrus: cs_dsp: Avoid padding bytes in
 cs_dsp_coeff_ctl

On Mon, Apr 25, 2022 at 10:51:59AM +0100, Richard Fitzgerald wrote:
> Change the order of members in struct cs_dsp_coeff_ctl to avoid
> the compiler having to insert alignment padding bytes. On a x86_64
> build this saves 16 bytes per control.
> 
> - Pointers are collected to the top of the struct (with the exception of
>   priv, as noted below), so that they are inherently aligned.
> - The set and enable bitflags are placed together so they can be merged.
> - priv is placed at the end of the struct - it is for use by the
>   client so it is helpful to make it stand out, and since the compiler
>   will always pad the struct size to an alignment multiple putting a
>   pointer last won't introduce any more padding.
> - struct cs_dsp_alg_region is placed at the end, right before priv, for
>   the same reasoning as priv.
> 
> Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
> ---

Reviewed-by: Charles Keepax <ckeepax@...nsource.cirrus.com>

Thanks,
Charles