linux-kernel - Re: [PATCH v2 34/65] clk: ux500: prcmu: Add a determine

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] [day] [month] [year] [list]

Message-ID: <20221109110548.4dcbkwx3jgjnhldw@houat>
Date:   Wed, 9 Nov 2022 12:05:48 +0100
From:   Maxime Ripard <maxime@...no.tech>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Stephen Boyd <sboyd@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Chen-Yu Tsai <wens@...e.org>, Daniel Vetter <daniel@...ll.ch>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Shawn Guo <shawnguo@...nel.org>,
        Fabio Estevam <festevam@...il.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        Michael Turquette <mturquette@...libre.com>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Paul Cercueil <paul@...pouillou.net>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Andreas Färber <afaerber@...e.de>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Abel Vesa <abelvesa@...nel.org>,
        Charles Keepax <ckeepax@...nsource.cirrus.com>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        Orson Zhai <orsonzhai@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Prashant Gaikwad <pgaikwad@...dia.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Samuel Holland <samuel@...lland.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Richard Fitzgerald <rf@...nsource.cirrus.com>,
        Vinod Koul <vkoul@...nel.org>,
        NXP Linux Team <linux-imx@....com>,
        Sekhar Nori <nsekhar@...com>,
        Kishon Vijay Abraham I <kishon@...nel.org>,
        Takashi Iwai <tiwai@...e.com>,
        David Airlie <airlied@...il.com>,
        Luca Ceresoli <luca.ceresoli@...tlin.com>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        David Lechner <david@...hnology.com>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Mark Brown <broonie@...nel.org>,
        Max Filippov <jcmvbkbc@...il.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        linux-stm32@...md-mailman.stormreply.com,
        alsa-devel@...a-project.org, linux-mediatek@...ts.infradead.org,
        linux-phy@...ts.infradead.org, linux-mips@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org,
        linux-actions@...ts.infradead.org, linux-clk@...r.kernel.org,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        patches@...nsource.cirrus.com, linux-tegra@...r.kernel.org,
        linux-rtc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-sunxi@...ts.linux.dev, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2 34/65] clk: ux500: prcmu: Add a determine_rate hook

Hi Linus,

On Tue, Nov 08, 2022 at 02:25:04PM +0100, Linus Walleij wrote:
> On Fri, Nov 4, 2022 at 2:32 PM Maxime Ripard <maxime@...no.tech> wrote:
> 
> > The UX500 PRCMU "clkout" clock implements a mux with a set_parent hook,
> > but doesn't provide a determine_rate implementation.
> >
> > This is a bit odd, since set_parent() is there to, as its name implies,
> > change the parent of a clock. However, the most likely candidate to
> > trigger that parent change is a call to clk_set_rate(), with
> > determine_rate() figuring out which parent is the best suited for a
> > given rate.
> >
> > The other trigger would be a call to clk_set_parent(), but it's far less
> > used, and it doesn't look like there's any obvious user for that clock.
> >
> > So, the set_parent hook is effectively unused, possibly because of an
> > oversight. However, it could also be an explicit decision by the
> > original author to avoid any reparenting but through an explicit call to
> > clk_set_parent().
> 
> It is actually set up from the device tree, typically like this:
> 
> /* clkout1 from ACLK divided by 8 */
> clocks = <&clkout_clk DB8500_CLKOUT_1 DB8500_CLKOUT_SRC_ACLK 8>;
> 
> So the parent (source) and divisor comes in there.
> 
> clk->source and clk->divider is already set up when clk_hw_register() is
> called.

I wasn't aware that we had such bindings. AFAIUI, it looks redundant
with assigned-clock-rates and assigned-clock-parents, could we deprecate
it?

> So set/get_parent() is never used on clkout.
> 
> I think I just added the callbacks for completeness, should we delete them
> altogether?

I can't really test any of these platforms, so I'm a bit wary of making
such changes myself. Feel free to send a follow-up if you think it's
needed :)

> The patch is probably fine as-is as well so
> Acked-by: Linus Walleij <linus.walleij@...aro.org>

Thanks!
Maxime