linux-kernel - Re: [PATCH 15/49] regmap-irq: Change the behavior of mask

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAHp75Vd7Sq9RMqin_y-8qUEAJLaGfuqxAbe+qcMB22=bqkyZqg@mail.gmail.com>
Date:   Tue, 21 Jun 2022 11:29:23 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Aidan MacDonald <aidanmacdonald.0x0@...il.com>
Cc:     Mark Brown <broonie@...nel.org>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Banajit Goswami <bgoswami@...eaurora.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Michael Walle <michael@...le.cc>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Cristian Ciocaltea <cristian.ciocaltea@...il.com>,
        Chen-Yu Tsai <wens@...e.org>, tharvey@...eworks.com,
        rjones@...eworks.com, Matti Vaittinen <mazziesaccount@...il.com>,
        orsonzhai@...il.com, baolin.wang7@...il.com, zhang.lyra@...il.com,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Samuel Holland <samuel@...lland.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        linux-actions@...ts.infradead.org,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        linux-sunxi@...ts.linux.dev,
        ALSA Development Mailing List <alsa-devel@...a-project.org>
Subject: Re: [PATCH 15/49] regmap-irq: Change the behavior of mask_writeonly

On Mon, Jun 20, 2022 at 10:08 PM Aidan MacDonald
<aidanmacdonald.0x0@...il.com> wrote:
>
> No drivers currently use mask_writeonly, and in its current form
> it seems a bit misleading. When set, mask registers will be
> updated with regmap_write_bits() instead of regmap_update_bits(),
> but regmap_write_bits() still does a read-modify-write under the
> hood. It's not a write-only operation.
>
> Performing a simple regmap_write() is probably more useful, since
> it can be used for chips that have separate set & clear registers
> for controlling mask bits. Such registers are normally volatile
> and read as 0, so avoiding a register read minimizes bus traffic.

Reading your explanations and the code, I would rather think about
fixing the regmap_write_bits() to be writeonly op.

Otherwise it's unclear what's the difference between
regmap_write_bits() vs. regmap_update_bits().

...

>         if (d->chip->mask_writeonly)
> -               return regmap_write_bits(d->map, reg, mask, val);
> +               return regmap_write(d->map, reg, val & mask);
>         else
>                 return regmap_update_bits(d->map, reg, mask, val);

-- 
With Best Regards,
Andy Shevchenko