linux-kernel - Re: [RESEND PATCH v5 3/6] dt-bindings: mvebu-uart: document DT bindings for marvell,armada-3700-uart-clock

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Message-ID: <CAL_JsqJ9UU8Q6LNha35uM6ie5-T1pd-FNSMuaf9ZBghU+KBfPA@mail.gmail.com>
Date:   Tue, 28 Sep 2021 12:57:08 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Pali Rohár <pali@...nel.org>
Cc:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Lunn <andrew@...n.ch>,
        Gregory Clement <gregory.clement@...tlin.com>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Vladimir Vid <vladimir.vid@...tura.hr>,
        Marek Behún <kabel@...nel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RESEND PATCH v5 3/6] dt-bindings: mvebu-uart: document DT
 bindings for marvell,armada-3700-uart-clock

On Mon, Sep 27, 2021 at 3:34 PM Pali Rohár <pali@...nel.org> wrote:
>
> On Monday 27 September 2021 15:17:59 Rob Herring wrote:
> > On Wed, Sep 22, 2021 at 5:56 AM Pali Rohár <pali@...nel.org> wrote:
> > >
> > > This change adds DT bindings documentation for device nodes with compatible
> > > string "marvell,armada-3700-uart-clock".
> >
> > Please resend to the DT list so that checks run and this gets reviewed
> > in a timely manner.
>
> OK
>
> > > Signed-off-by: Pali Rohár <pali@...nel.org>
> > > ---
> > >  .../bindings/clock/armada3700-uart-clock.yaml | 57 +++++++++++++++++++
> > >  1 file changed, 57 insertions(+)
> > >  create mode 100644 Documentation/devicetree/bindings/clock/armada3700-uart-clock.yaml
> > >
> > > diff --git a/Documentation/devicetree/bindings/clock/armada3700-uart-clock.yaml b/Documentation/devicetree/bindings/clock/armada3700-uart-clock.yaml
> > > new file mode 100644
> > > index 000000000000..5bdb23e0ba3e
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/clock/armada3700-uart-clock.yaml
> > > @@ -0,0 +1,57 @@
> > > +# SPDX-License-Identifier: GPL-2.0
> >
> > Dual license. checkpatch will tell you which ones.
>
> OK
>
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/clock/marvell,armada-3700-uart-clock#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +title: Marvell Armada 3720 UART clocks
> > > +
> > > +properties:
> > > +  compatible:
> > > +    const: marvell,armada-3700-uart-clock
> > > +
> > > +  reg:
> > > +    items:
> > > +      - description: UART Clock Control Register
> > > +      - description: UART 2 Baud Rate Divisor Register
> > > +
> > > +  clocks:
> > > +    description: |
> > > +      List of parent clocks suitable for UART from following set:
> > > +        "TBG-A-P", "TBG-B-P", "TBG-A-S", "TBG-B-S", "xtal"
> > > +      UART clock can use one from this set and when more are provided
> > > +      then kernel would choose and configure the most suitable one.
> > > +      It is suggest to specify at least one TBG clock to achieve
> > > +      baudrates above 230400 and also to specify clock which bootloader
> > > +      used for UART (most probably xtal) for smooth boot log on UART.
> > > +
> > > +  clock-names:
> > > +    items:
> > > +      - const: TBG-A-P
> > > +      - const: TBG-B-P
> > > +      - const: TBG-A-S
> > > +      - const: TBG-B-S
> > > +      - const: xtal
> > > +    minItems: 1
> > > +    maxItems: 5
> >
> > Don't need maxItems equal to length of 'items'.
>
> OK
>
> > > +
> > > +  '#clock-cells':
> > > +    const: 1
> > > +
> > > +required:
> > > +  - compatible
> > > +  - reg
> > > +  - clocks
> > > +  - clock-names
> > > +  - '#clock-cells'
> > > +
> > > +additionalProperties: false
> > > +
> > > +examples:
> > > +  - |
> > > +    uartclk: uartclk@...00 {
> >
> > clock-controller@...10
> >
> > > +      compatible = "marvell,armada-3700-uart-clock";
> > > +      reg = <0x12010 0x4>, <0x12210 0x4>;
> >
> > However, looks like this is part of some other block.
>
> Yes, it is part of UART block.
>
> Explanation is in commit message of patch 2/6.
>
> And also discussed here:
> https://lore.kernel.org/linux-serial/20210812200804.i4kbcs6ut27mapd3@pali/
>
> > The whole block
> > needs a binding (or at least the parent and whatever sub-functions you
> > know about).
>
> Whole UART block has already binding. Clock driver just needs access to
> these clock bits of these two registers which are in UART block. HW
> designers decided that clock which drives UART2 has configuration in
> UART1 address space. As explained in commit message of patch 2/6 there
> is no easy way how to deal with it in DTS backward compatible way. So
> clock and UART driver shares mutex for accessing these two shared
> registers, and these two registers are defined in all 3 DT nodes: UART1,
> UART2 and UART-clock.

That's awful. I guess I don't have a better suggestion.

Rob