linux-kernel - Re: [STLinux Kernel] [PATCH 8/8] ARM: dts: STiH407-family: Enable HW flow-control

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Message-ID: <20170127113352.paie6vzo23ax7nxt@dell>
Date:   Fri, 27 Jan 2017 11:33:52 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Peter Griffin <peter.griffin@...aro.org>
Cc:     gregkh@...uxfoundation.org, jslaby@...e.com,
        linux-serial@...r.kernel.org, robh+dt@...nel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kernel@...inux.com
Subject: Re: [STLinux Kernel] [PATCH 8/8] ARM: dts: STiH407-family: Enable HW
 flow-control

On Wed, 25 Jan 2017, Peter Griffin wrote:
> On Wed, 25 Jan 2017, Peter Griffin wrote:
> > 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@...aro.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.
> 
> Thinking some more this generic binding definition is a bit restrictive,
> particularly the "Note that this property is mutually-exclusive with "cts-gpios"
> and "rts-gpios"" part.
> 
> As with this series we will have dynamic on-the-fly changing from hw flow
> control to gpio control for other configs which the HW IP doesn't support.
> 
> IMO the uart-has-rtscts definition should be updated to reflect that they can
> be used together in certain circumstances.

Ah, you noticed that too.  Yes, will update the doc.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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