linux-kernel - Re: [PATCH] arm: dts: gr-peach: Reduce extal

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Message-ID: <20171005074859.GN4037@w540>
Date:   Thu, 5 Oct 2017 09:48:59 +0200
From:   jacopo mondi <jacopo@...ndi.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Simon Horman <horms@...ge.net.au>,
        Magnus Damm <magnus.damm@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Chris Brandt <Chris.Brandt@...esas.com>
Subject: Re: [PATCH] arm: dts: gr-peach: Reduce extal_clk resolution

Hi Geert

On Wed, Oct 04, 2017 at 05:54:46PM +0200, Geert Uytterhoeven wrote:
> Hi Jacopo,
>
> On Wed, Oct 4, 2017 at 5:40 PM, Jacopo Mondi <jacopo+renesas@...ndi.org> wrote:
> > The system clock described by extal_clk is reported to have a frequency
> > of 13.333 Mhz and is correctly described by gr-peach device tree.
> >
> > However, when enabling a RIIC device the following error is reported by
> > drivers/i2c/busses/i2c-riic.c
> >
> > "invalid parent clk (33332500). Must be 33325000Hz"
> >
> > As RIIC devices have a clock source obtained by dividing by 12 the
> > system clock, the resulting value is not accepted by the driver
> > (which clearly states not to support any frequency except the reported
> > 33325000Hz one).
> >
> > Hence, reduce the system clock accuracy to a value which makes
> > frequencies obtained through division accepted by RIIC driver.
> >
> > Please note that other r7s72100 boards, such as Genmai, report the same
> > "reduced accuracy" frequency, even if their external clock sources are
> > effectively 13.333Mhz as gr-peach one.
> >
> > Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
>
> There's no need to do this, Chris already proposed a fix, cfr.
> "[PATCH v2] i2c: riic: remove fixed clock restriction"
> (https://www.spinics.net/lists/linux-renesas-soc/msg18573.html).

Oh that's even better!
Do you see any value in augmenting the frequency resolution in Genmai
DTS then?

Thanks
  j

>
> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds