linux-kernel - Re: [PATCH v3 56/65] clk: ingenic: cgu: Switch to 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] [thread-next>] [day] [month] [year] [list]

Message-ID: <o6odr3i3ypj6p6vxuiwgymll3bew544mwzcgs6hjzum5uix43j@galqy4lxjdvx>
Date:   Wed, 5 Apr 2023 17:19:06 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Andreas Färber <afaerber@...e.de>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        Max Filippov <jcmvbkbc@...il.com>,
        Charles Keepax <ckeepax@...nsource.cirrus.com>,
        Richard Fitzgerald <rf@...nsource.cirrus.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Luca Ceresoli <luca.ceresoli@...tlin.com>,
        David Lechner <david@...hnology.com>,
        Sekhar Nori <nsekhar@...com>, Abel Vesa <abelvesa@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        Prashant Gaikwad <pgaikwad@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, Vinod Koul <vkoul@...nel.org>,
        Kishon Vijay Abraham I <kishon@...nel.org>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Samuel Holland <samuel@...lland.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Orson Zhai <orsonzhai@...il.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-actions@...ts.infradead.org, patches@...nsource.cirrus.com,
        linux-stm32@...md-mailman.stormreply.com,
        linux-mediatek@...ts.infradead.org,
        linux-renesas-soc@...r.kernel.org, linux-tegra@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-phy@...ts.infradead.org,
        linux-rtc@...r.kernel.org, linux-sunxi@...ts.linux.dev,
        alsa-devel@...a-project.org, linux-mips@...r.kernel.org
Subject: Re: [PATCH v3 56/65] clk: ingenic: cgu: Switch to determine_rate

Hi Paul,

On Wed, Apr 05, 2023 at 03:04:05PM +0200, Paul Cercueil wrote:
> Le mardi 04 avril 2023 à 12:11 +0200, Maxime Ripard a écrit :
> > The Ingenic CGU clocks 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().
> 
> As I said in the v2 (IIRC), clk_set_parent() is used when re-parenting
> from the device tree.

Yep, it's indeed an oversight in the commit log.

> > The driver does implement round_rate() though, which means that we
> > can
> > change the rate of the clock, but we will never get to change the
> > parent.
> > 
> > However, It's hard to tell whether it's been done on purpose or not.
> > 
> > Since we'll start mandating a determine_rate() implementation, let's
> > convert the round_rate() implementation to a determine_rate(), which
> > will also make the current behavior explicit. And if it was an
> > oversight, the clock behaviour can be adjusted later on.
> 
> So just to be sure, this patch won't make clk_set_rate() automatically
> switch parents, right?
> 
> Allowing automatic re-parenting sounds like a huge can of worms...

The behaviour is strictly equivalent before that patch and after: the
driver will not reparent on a rate change. It just makes it explicit.

Maxime

Download attachment "signature.asc" of type "application/pgp-signature" (229 bytes)