Re: [PATCH 4/4] tty: serial: 8250_mtk: Add support for bus clock

[Sascha Hauer]

On Tue, May 05, 2015 at 05:41:16PM +0200, Matthias Brugger wrote:
> 2015-04-27 8:49 GMT+02:00 Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>:
> > 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@xxxxxxxxxxxxxx>
> > ---
> >  .../devicetree/bindings/serial/mtk-uart.txt        | 12 ++++++++--
> >  drivers/tty/serial/8250/8250_mtk.c                 | 28 ++++++++++++++++++----
> >  2 files changed, 34 insertions(+), 6 deletions(-)
> >
> > diff --git a/Documentation/devicetree/bindings/serial/mtk-uart.txt b/Documentation/devicetree/bindings/serial/mtk-uart.txt
> > index 4415226..8d63f1d 100644
> > --- a/Documentation/devicetree/bindings/serial/mtk-uart.txt
> > +++ b/Documentation/devicetree/bindings/serial/mtk-uart.txt
> > @@ -14,7 +14,14 @@ 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)
> > +
> > +For compatibility with older device trees an unnamed clock is used for the
> > +baud clock if the baudclk does not exist. Do not use this for new designs.
> >
> >  Example:
> >
> > @@ -22,5 +29,6 @@ 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..8eb3876 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;
> >  };
> 
> Not sure if it would be better to rename the uart_clk to baud_clk
> which reflects the new naming scheme.

Can do.

> 
> >
> >  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);
> 
> bus_clk can be NULL.

The clk core handles NULL clks just fine. They are considered dummy
clks. You can prepare/enable them, clk_get_rate of course returns
nothing useful.

Sascha

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