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    SubjectRe: [STLinux Kernel] [PATCH 8/8] ARM: dts: STiH407-family: Enable HW flow-control
    On Wed, 25 Jan 2017, Peter Griffin wrote:

    > Hi Lee,
    >
    > On Tue, 24 Jan 2017, Lee Jones wrote:
    >
    > > Hardware flow-control capability must be specified at a platform
    > > level in order to inform the ASC driver that the platform is capable
    > > (i.e. are the lines wired up, etc). STiH4{07,10} devices are indeed
    > > capable, so let's provide the property.
    > >
    > > Signed-off-by: Lee Jones <lee.jones@linaro.org>
    > > ---
    > > arch/arm/boot/dts/stih407-family.dtsi | 2 +-
    > > 1 file changed, 1 insertion(+), 1 deletion(-)
    > >
    > > diff --git a/arch/arm/boot/dts/stih407-family.dtsi b/arch/arm/boot/dts/stih407-family.dtsi
    > > index 9789978..7ada8ea 100644
    > > --- a/arch/arm/boot/dts/stih407-family.dtsi
    > > +++ b/arch/arm/boot/dts/stih407-family.dtsi
    > > @@ -226,7 +226,7 @@
    > > pinctrl-0 = <&pinctrl_serial0_flowctrl>;
    > > pinctrl-1 = <&pinctrl_serial0>;
    > > clocks = <&clk_s_c0_flexgen CLK_EXT2F_A9>;
    > > -
    > > + st,hw-flow-control;
    >
    > There is a generic serial binding for this already. As this ST property
    > hasn't been used upstream, it seems like it would be worth dropping it
    > and switching to the generic uart-has-rtscts one.
    >
    > See Documentation/devicetree/bindings/serial/serial.txt
    >
    > - uart-has-rtscts: The presence of this property indicates that the
    > UART has dedicated lines for RTS/CTS hardware flow control, and that
    > they are available for use (wired and enabled by pinmux configuration).
    > This depends on both the UART hardware and the board wiring.
    > Note that this property is mutually-exclusive with "cts-gpios" and
    > "rts-gpios" above.

    I've done some digging and I can't see anywhere where
    st,hw-flow-control is being used, even in the BSP kernel(s). It's
    also not documented in dt-bindings. With that in mind, I think it's
    probably okay to use the generic binding.

    Although, the "Note" at the bottom of the uart-has-rtscts is not
    correct in our case, since we handle the case dynamically.

    > Also you should put this in the board dtsi, as it is board dependent property.
    > By putting it here you are enabling hw-flow-control for all stih407-family
    > based boards.

    Fair shout.

    On the B2120 UART0 is hooked up to the Smart Card Reader.

    Will fix.

    --
    Lee Jones
    Linaro STMicroelectronics Landing Team Lead
    Linaro.org │ Open source software for ARM SoCs
    Follow Linaro: Facebook | Twitter | Blog

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