linux-kernel - Re: [PATCH v2 4/6] dt: bindings: add mt7621-pll dt binding documentation

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Date:   Sat, 17 Aug 2019 22:42:12 +0800
From:   Chuanhong Guo <gch981213@...il.com>
To:     Rob Herring <robh@...nel.org>
Cc:     "open list:COMMON CLK FRAMEWORK" <linux-clk@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:MIPS" <linux-mips@...r.kernel.org>,
        "open list:STAGING SUBSYSTEM" <devel@...verdev.osuosl.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        John Crispin <john@...ozen.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Weijie Gao <hackpascal@...il.com>, NeilBrown <neil@...wn.name>
Subject: Re: [PATCH v2 4/6] dt: bindings: add mt7621-pll dt binding documentation

Hi!

On Tue, Aug 13, 2019 at 11:51 PM Rob Herring <robh@...nel.org> wrote:
> [...]
> > +Example:
> > +     pll {
> > +             compatible = "mediatek,mt7621-pll";
>
> You didn't answer Stephen's question on v1.

I thought he was asking why there's a syscon in compatible string. I
noticed that the syscon in my previous patch is a copy-paste error
from elsewhere and dropped it.

>
> Based on this binding, there is no way to control/program the PLL. Is
> this part of some IP block?

The entire section is called "system control" in datasheet and is
occupied in arch/mips/ralink/mt7621.c [0]
Two clocks provided here is determined by reading some read-only
registers in this part.
There's another register in this section providing clock gates for
every peripherals, but MTK doesn't provide a clock plan in their
datasheet. I can't determine corresponding clock frequencies for every
peripherals, thus unable to write a working clock driver.

>
> > +
> > +             #clock-cells = <1>;
> > +             clock-output-names = "cpu", "bus";
> > +     };
> > --
> > 2.21.0
> >

Regards,
Chuanhong Guo

[0] https://elixir.bootlin.com/linux/latest/source/arch/mips/ralink/mt7621.c#L156