linux-kernel - Re: [PATCH v4 3/6] dt-bindings: mvebu-uart: document DT bindings for marvell,armada-3700-uart-clock

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Message-ID: <162879679919.19113.10297499909721773583@swboyd.mtv.corp.google.com>
Date:   Thu, 12 Aug 2021 12:33:19 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     <pali@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh+dt@...nel.org>, Andrew Lunn <andrew@...n.ch>,
        Gregory Clement <gregory.clement@...tlin.com>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Vladimir Vid <vladimir.vid@...tura.hr>, kabel@...nel.org,
        linux-clk@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 3/6] dt-bindings: mvebu-uart: document DT bindings for marvell,armada-3700-uart-clock

Quoting Pali (2021-08-06 01:28:18)
> On Thursday 05 August 2021 17:30:19 Stephen Boyd wrote:
> > > 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..5ef04f3affda
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/clock/armada3700-uart-clock.yaml
> > > @@ -0,0 +1,49 @@
> > > +# SPDX-License-Identifier: GPL-2.0
> > > +%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
> > 
> > Please add a newline here
> > 
> > > +properties:
> > > +  compatible:
> > > +    const: marvell,armada-3700-uart-clock
> > 
> > Please add a newline here
> > 
> > > +  reg:
> > > +    items:
> > > +      - description: UART Clock Control Register
> > > +      - description: UART 2 Baud Rate Divisor Register
> > 
> > Please add a newline here
> > 
> > > +  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.
> > 
> > Please use items and const like clock-names for the clocks property.
> 
> It is already there, see below.
> 
> > The description makes me feel like the DT is configuring the choices
> > available.
> 
> See description. It is kernel (driver) who is choosing one clock from
> the set and then configure it a UART clock.

Can that be done with assigned-clock-parents?

> 
> > Ideally, the clocks and clock-names properties are fixed in
> > length and never change unless the compatible changes.
> > 
> > Please add a newline here
> > 
> > > +  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
> > 
> > Please add a newline here
> > 
> > > +  '#clock-cells':
> > > +    const: 1
> > 
> > Please add a newline here
> > 
> > > +required:
> > > +  - compatible
> > > +  - reg
> > > +  - clocks
> > > +  - clock-names
> > > +  - '#clock-cells'
> > 
> > Please add a newline here
> > 
> > > +additionalProperties: false
> > 
> > Please add a newline here
> > 
> > > +examples:
> > > +  - |
> > > +    uartclk: uartclk@...00 {
> > > +      compatible = "marvell,armada-3700-uart-clock";
> > > +      reg = <0x12010 0x4>, <0x12210 0x4>;

The reg property looks like this is poking a mux that is part of a
larger device. What device is this actually part of? The uart hardware?

> > > +      clocks = <&tbg 0>, <&tbg 1>, <&tbg 2>, <&tbg 3>, <&xtalclk>;
> > > +      clock-names = "TBG-A-P", "TBG-B-P", "TBG-A-S", "TBG-B-S", "xtal";