linux-kernel - Re: [PATCH V4 2/5] clocksource/drivers/sysctr: Add clock-frequency property

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Message-ID: <CAL_JsqJbHFZ2qcLvhZGk8Q-f80_QhdgQxcHe2TyCjc4GGRNJNQ@mail.gmail.com>
Date:   Wed, 10 Jul 2019 07:23:23 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Anson Huang <anson.huang@....com>
Cc:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mark Rutland <mark.rutland@....com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Sascha Hauer <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        Leonard Crestez <leonard.crestez@....com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Daniel Baluta <daniel.baluta@....com>,
        Jacky Bai <ping.bai@....com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Abel Vesa <abel.vesa@....com>,
        Andrey Smirnov <andrew.smirnov@...il.com>,
        Carlo Caione <ccaione@...libre.com>,
        "Angus Ainslie (Purism)" <angus@...ea.ca>,
        Guido Günther <agx@...xcpu.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH V4 2/5] clocksource/drivers/sysctr: Add clock-frequency property

On Tue, Jul 9, 2019 at 7:30 PM Anson Huang <anson.huang@....com> wrote:
>
> Hi, Rob
>
> > On Mon, Jul 1, 2019 at 3:47 AM <Anson.Huang@....com> wrote:
> > >
> > > From: Anson Huang <Anson.Huang@....com>
> >
> > 'dt-bindings: timer: ...' for the subject.
>
> OK, I made a mistake.
>
> >
> > >
> > > Systems which use platform driver model for clock driver require the
> > > clock frequency to be supplied via device tree when system counter
> > > driver is enabled.
> >
> > This is a DT binding. What's a platform driver?
>
> It is just trying to explain why we need to introduce this "clock-frequency"
> property, nothing about the binding and platform driver.
>
> >
> > >
> > > This is necessary as in the platform driver model the of_clk
> > > operations do not work correctly because system counter driver is
> > > initialized in early phase of system boot up, and clock driver using
> > > platform driver model is NOT ready at that time, it will cause system
> > > counter driver initialization failed.
> > >
> > > Add clock-frequency property to the device tree bindings of the NXP
> > > system counter, so the driver can tell timer-of driver to get clock
> > > frequency from DT directly instead of doing of_clk operations via clk
> > > APIs.
> >
> > While you've now given a good explanation why you need this, it all sounds
> > like linux specific issues and a DT change should not be necessary.
> >
> > Presumably, 'clocks' points to a fixed-clock node, right? Just parse the 'clocks'
> > phandle and fetch the frequency from that node if you need to get the
> > frequency 'early'.
>
> Sound like a better solution, I will try that, since the system counter's clock is
> from osc_24m and divided by 3, since different platforms may have different divider,
> so maybe I can create a fixed-clock node in DT, then system counter driver can parse
> the clock and fetch the frequency from that node, will redo a V5 patch.

The divide by 3 can be implied by the compatible. If you need a
different divider, add another compatible.

> >
> > > Signed-off-by: Anson Huang <Anson.Huang@....com>
> > > ---
> > > No change.
> > > ---
> > >  .../devicetree/bindings/timer/nxp,sysctr-timer.txt        | 15 +++++++++------
> > >  1 file changed, 9 insertions(+), 6 deletions(-)
> > >
> > > diff --git
> > > a/Documentation/devicetree/bindings/timer/nxp,sysctr-timer.txt
> > > b/Documentation/devicetree/bindings/timer/nxp,sysctr-timer.txt
> > > index d576599..7088a0e 100644
> > > --- a/Documentation/devicetree/bindings/timer/nxp,sysctr-timer.txt
> > > +++ b/Documentation/devicetree/bindings/timer/nxp,sysctr-timer.txt
> > > @@ -11,15 +11,18 @@ Required properties:
> > >  - reg :             Specifies the base physical address and size of the comapre
> > >                      frame and the counter control, read & compare.
> > >  - interrupts :      should be the first compare frames' interrupt
> > > -- clocks :         Specifies the counter clock.
> > > -- clock-names:             Specifies the clock's name of this module
> > > +- clocks :          Specifies the counter clock, mutually exclusive with clock-
> > frequency.
> > > +- clock-names :     Specifies the clock's name of this module, mutually
> > exclusive with
> > > +                   clock-frequency.
> > > +- clock-frequency : Specifies system counter clock frequency, mutually
> > exclusive with
> > > +                   clocks/clock-names.
> >
> > It doesn't really work to say one or the other is needed unless you make the
> > OS support both cases.
>
> The OS already support both cases now with this patch series.

What about FreeBSD or any other OS?

Rob