linux-kernel - Re: [PATCH RESEND 5/5] ARM: dts: berlin: add the pinctrl node and muxing setup for uarts

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Message-ID: <20140411090936.GC20147@kwain>
Date:	Fri, 11 Apr 2014 11:09:36 +0200
From:	Antoine Ténart 
	<antoine.tenart@...e-electrons.com>
To:	Andrew Lunn <andrew@...n.ch>
Cc:	sebastian.hesselbarth@...il.com, linus.walleij@...aro.org,
	zmxu@...vell.com, jszhang@...vell.com, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, alexandre.belloni@...e-electrons.com,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH RESEND 5/5] ARM: dts: berlin: add the pinctrl node and
 muxing setup for uarts

Hi Andrew,

On Fri, Apr 11, 2014 at 10:18:59AM +0200, Andrew Lunn wrote:
> On Thu, Apr 10, 2014 at 03:07:54PM +0200, Antoine Ténart wrote:
> > The uart0 pinmux configuration is in the dtsi because uart0 will always
> > use uart0-pmux to work, no other possibility. Same thing for uart1.
> > 
> > Signed-off-by: Antoine Ténart <antoine.tenart@...e-electrons.com>
> > ---
> >  arch/arm/boot/dts/berlin2.dtsi   | 20 ++++++++++++++++++++
> >  arch/arm/boot/dts/berlin2cd.dtsi | 13 +++++++++++++
> >  arch/arm/boot/dts/berlin2q.dtsi  | 20 ++++++++++++++++++++
> >  3 files changed, 53 insertions(+)
> > 
> > diff --git a/arch/arm/boot/dts/berlin2.dtsi b/arch/arm/boot/dts/berlin2.dtsi
> > index 56a1af2f1052..43eb90c36050 100644
> > --- a/arch/arm/boot/dts/berlin2.dtsi
> > +++ b/arch/arm/boot/dts/berlin2.dtsi
> > @@ -176,6 +176,22 @@
> >  			};
> >  		};
> >  
> > +		pinctrl: pinctrl@0 {
> > +			compatible = "marvell,berlin2-pinctrl";
> > +			reg = <0xea0000 0x08>, <0xfc0000 0x44>;
> > +			reg-names = "global_base", "apb_base";
> > +
> > +			uart0_pmux: uart0-pmux {
> > +				berlin,group = "GSM4";
> > +				berlin,function = <0>;
> > +			};
> > +
> > +			uart1_pmux: uart1-pmux {
> > +				berlin,group = "GSM5";
> > +				berlin,function = <1>;
> 
> Hi Antoine
> 
> This very much looks like black magic.
> 
> I assume the data sheet is not available? So i think you need to
> document all possible combinations of values of group and function.
> Maybe you can add a file in
> 
> arch/arm/boot/dts/include/dt-bindings/pinctrl/
> 
> with something like
> 
> #define GSM4_UART0	0
> #define GSM5_UART1	1
> #define GSM12_UART0	1
> #define GSM12_IrDA0	1
> #define GSM12_GPIO	2

Groups' functions are not the same between BG2/BG2CD and BG2Q so multiple
headers would be needed which may not be a good thing. Some platforms use black
magic, and we can find a pinmux configuration for OMAP looking like:

0x128 (PIN_INPUT_PULLUP | MUX_MODE0)

Weel, we could explicitly define the functions in the driver itself and use in
the dt something like:

berlin,group = "GSM4";
berlin,function = "uart0";

This is what's done on the sunxi's pinctrl.

Antoine

-- 
Antoine Ténart, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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