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: <20211015093701.pfvkighxsndj4ujg@pali>
Date:   Fri, 15 Oct 2021 11:37:01 +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 Friday 15 October 2021 11:09:37 Pali Rohár wrote:
> 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.

It is explained also in commit message of patch 2/6.

> > > +      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
> > >