linux-kernel - Re: [PATCH 4/4] tty: serial: 8250

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Message-ID: <CABuKBe+ebskWHVRtcfei9hZVvt5oHA0wij0WuLCkYqJo0Hzm=Q@mail.gmail.com>
Date:	Fri, 24 Apr 2015 13:18:07 +0200
From:	Matthias Brugger <matthias.bgg@...il.com>
To:	Sascha Hauer <s.hauer@...gutronix.de>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	linux-mediatek@...ts.infradead.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	linux-serial@...r.kernel.org, Alan Cox <alan@...ux.intel.com>
Subject: Re: [PATCH 4/4] tty: serial: 8250_mtk: Add support for bus clock

2015-04-23 10:51 GMT+02:00 Sascha Hauer <s.hauer@...gutronix.de>:
> The mtk 8250 needs two clocks, one for providing the baudrate and
> one that needs to be enabled for register accesses. The latter has
> not been supported, this patch adds support for it. It is optional
> for now since not all SoCs provide a bus clock.
>
> Signed-off-by: Sascha Hauer <s.hauer@...gutronix.de>
> ---
>  Documentation/devicetree/bindings/serial/mtk-uart.txt |  9 +++++++--
>  drivers/tty/serial/8250/8250_mtk.c                    | 14 +++++++++++++-
>  2 files changed, 20 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/serial/mtk-uart.txt b/Documentation/devicetree/bindings/serial/mtk-uart.txt
> index 4415226..369b5c3 100644
> --- a/Documentation/devicetree/bindings/serial/mtk-uart.txt
> +++ b/Documentation/devicetree/bindings/serial/mtk-uart.txt
> @@ -14,7 +14,11 @@ Required properties:
>
>  - interrupts: A single interrupt specifier.
>
> -- clocks: Clock driving the hardware.
> +- clocks : Must contain an entry for each entry in clock-names.
> +  See ../clocks/clock-bindings.txt for details.
> +- clock-names:
> +  - "baud": The clock the baudrate is derived from
> +  - "bus": The bus clock for register accesses (optional)
>
>  Example:
>
> @@ -22,5 +26,6 @@ Example:
>                 compatible = "mediatek,mt6589-uart", "mediatek,mt6577-uart";
>                 reg = <0x11006000 0x400>;
>                 interrupts = <GIC_SPI 51 IRQ_TYPE_LEVEL_LOW>;
> -               clocks = <&uart_clk>;
> +               clocks = <&uart_clk>, <&bus_clk>;
> +               clock-names = "baud", "bus";
>         };
> diff --git a/drivers/tty/serial/8250/8250_mtk.c b/drivers/tty/serial/8250/8250_mtk.c
> index 2f28bd0..20c27f0 100644
> --- a/drivers/tty/serial/8250/8250_mtk.c
> +++ b/drivers/tty/serial/8250/8250_mtk.c
> @@ -34,6 +34,7 @@
>  struct mtk8250_data {
>         int                     line;
>         struct clk              *uart_clk;
> +       struct clk              *bus_clk;
>  };
>
>  static void
> @@ -120,6 +121,7 @@ static int mtk8250_runtime_suspend(struct device *dev)
>         struct mtk8250_data *data = dev_get_drvdata(dev);
>
>         clk_disable_unprepare(data->uart_clk);
> +       clk_disable_unprepare(data->bus_clk);
>
>         return 0;
>  }
> @@ -135,6 +137,12 @@ static int mtk8250_runtime_resume(struct device *dev)
>                 return err;
>         }
>
> +       err = clk_prepare_enable(data->bus_clk);
> +       if (err) {
> +               dev_warn(dev, "Can't enable bus clock\n");
> +               return err;
> +       }
> +
>         return 0;
>  }
>
> @@ -153,7 +161,7 @@ mtk8250_do_pm(struct uart_port *port, unsigned int state, unsigned int old)
>  static int mtk8250_probe_of(struct platform_device *pdev, struct uart_port *p,
>                            struct mtk8250_data *data)
>  {
> -       data->uart_clk = devm_clk_get(&pdev->dev, NULL);
> +       data->uart_clk = devm_clk_get(&pdev->dev, "baud");
>         if (IS_ERR(data->uart_clk)) {
>                 dev_warn(&pdev->dev, "Can't get uart clock\n");
>                 return PTR_ERR(data->uart_clk);
> @@ -161,6 +169,10 @@ static int mtk8250_probe_of(struct platform_device *pdev, struct uart_port *p,
>
>         p->uartclk = clk_get_rate(data->uart_clk);
>
> +       data->bus_clk = devm_clk_get(&pdev->dev, "bus");
> +       if (IS_ERR(data->bus_clk))
> +               data->bus_clk = NULL;
> +

We have to take into account the old DTS definition. This means, that
if devm_clk_get(&pdev->dev, "baud") fails, we have to look for
devm_clk_get(&pdev->dev, NULL).
Only in the case I when clock "baud" does exist, do we check for clock
"bus". Does this make sense?

The backwards compatibility should be reflected in the bindings
documentation as well.

Cheers,
Matthias

-- 
motzblog.wordpress.com
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