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Message-ID: <3c1c42baf7d764bf6429b470f534fd9ec46ddedd.camel@crapouillou.net>
Date:   Wed, 05 Apr 2023 15:04:05 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Maxime Ripard <maxime@...no.tech>,
        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>
Cc:     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 Maxime,

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.

> 
> 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...

Cheers,
-Paul

> 
> Signed-off-by: Maxime Ripard <maxime@...no.tech>
> ---
>  drivers/clk/ingenic/cgu.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/clk/ingenic/cgu.c b/drivers/clk/ingenic/cgu.c
> index 1f7ba30f5a1b..0c9c8344ad11 100644
> --- a/drivers/clk/ingenic/cgu.c
> +++ b/drivers/clk/ingenic/cgu.c
> @@ -491,22 +491,23 @@ ingenic_clk_calc_div(struct clk_hw *hw,
>         return div;
>  }
>  
> -static long
> -ingenic_clk_round_rate(struct clk_hw *hw, unsigned long req_rate,
> -                      unsigned long *parent_rate)
> +static int ingenic_clk_determine_rate(struct clk_hw *hw,
> +                                     struct clk_rate_request *req)
>  {
>         struct ingenic_clk *ingenic_clk = to_ingenic_clk(hw);
>         const struct ingenic_cgu_clk_info *clk_info =
> to_clk_info(ingenic_clk);
>         unsigned int div = 1;
>  
>         if (clk_info->type & CGU_CLK_DIV)
> -               div = ingenic_clk_calc_div(hw, clk_info,
> *parent_rate, req_rate);
> +               div = ingenic_clk_calc_div(hw, clk_info, req-
> >best_parent_rate,
> +                                          req->rate);
>         else if (clk_info->type & CGU_CLK_FIXDIV)
>                 div = clk_info->fixdiv.div;
>         else if (clk_hw_can_set_rate_parent(hw))
> -               *parent_rate = req_rate;
> +               req->best_parent_rate = req->rate;
>  
> -       return DIV_ROUND_UP(*parent_rate, div);
> +       req->rate = DIV_ROUND_UP(req->best_parent_rate, div);
> +       return 0;
>  }
>  
>  static inline int ingenic_clk_check_stable(struct ingenic_cgu *cgu,
> @@ -626,7 +627,7 @@ static const struct clk_ops ingenic_clk_ops = {
>         .set_parent = ingenic_clk_set_parent,
>  
>         .recalc_rate = ingenic_clk_recalc_rate,
> -       .round_rate = ingenic_clk_round_rate,
> +       .determine_rate = ingenic_clk_determine_rate,
>         .set_rate = ingenic_clk_set_rate,
>  
>         .enable = ingenic_clk_enable,
> 

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