linux-kernel - Re: [PATCH v7 3/6] dt-bindings: mvebu-uart: document DT bindings for marvell,armada-3700-uart-clock

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Message-ID: <20211015090937.gnt66hgugrhwnkei@pali>
Date:   Fri, 15 Oct 2021 11:09:37 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Stephen Boyd <sboyd@...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>,
        Marek Behún <kabel@...nel.org>,
        linux-clk@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v7 3/6] dt-bindings: mvebu-uart: document DT bindings for
 marvell,armada-3700-uart-clock

On Thursday 14 October 2021 17:13:03 Stephen Boyd wrote:
> Quoting Pali Rohár (2021-09-30 02:58:35)
> > diff --git a/Documentation/devicetree/bindings/clock/marvell,armada-3700-uart-clock.yaml b/Documentation/devicetree/bindings/clock/marvell,armada-3700-uart-clock.yaml
> > new file mode 100644
> > index 000000000000..175f5c8f2bc5
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/clock/marvell,armada-3700-uart-clock.yaml
> > @@ -0,0 +1,59 @@
> [..]
> > +  '#clock-cells':
> > +    const: 1
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +  - clocks
> > +  - clock-names
> > +  - '#clock-cells'
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    uartclk: clock-controller@...10 {
> 
> The uart device is at 0x12000 and the clock-controller is at 0x12010?
> This looks like a node is being put into DT to represent a clk driver.
> Why can't we register a clk from the uart device driver itself? I think
> we talked about this a month or two ago but it still isn't clear to me.

We have already talked about it and I have already wrote reasons. UART
clk is shared for both UART1 and UART2. And UART clk regs are in both
address spaces of UART1 and UART2. UART1 or UART2 can be independently
disabled on particular board (as pins are MPP which may be configured to
different function). So you have a board only with UART2, you have to
disable UART1 node, but at the same time you have to access UART clk to
drive UART2. And UART clk bits are in UART1 address space.

> > +      compatible = "marvell,armada-3700-uart-clock";
> > +      reg = <0x12010 0x4>, <0x12210 0x4>;
> > +      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";
> > +      #clock-cells = <1>;
> > +    };
> > -- 
> > 2.20.1
> >