linux-kernel - Re: [PATCH] ARM: dts: mvebu: Fix armada-385-turris-omnia stdout-path

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Message-ID: <0f51c7a1-6d52-3e3e-edfe-e7b10917ecab@suse.de>
Date:   Sun, 27 Nov 2016 23:14:37 +0100
From:   Andreas Färber <afaerber@...e.de>
To:     Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Mark Rutland <mark.rutland@....com>,
        Andrew Lunn <andrew@...n.ch>,
        Jason Cooper <jason@...edaemon.net>,
        devicetree@...r.kernel.org, Tomas Hlavacek <tomas.hlavacek@....cz>,
        Russell King <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Gregory Clement <gregory.clement@...e-electrons.com>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Bedřicha Košatu <bedrich.kosata@....cz>,
        Michal Hrusecki <Michal.Hrusecky@....cz>
Subject: Re: [PATCH] ARM: dts: mvebu: Fix armada-385-turris-omnia stdout-path

Am 27.11.2016 um 22:25 schrieb Uwe Kleine-König:
> On Sun, Nov 27, 2016 at 08:37:24PM +0100, Andreas Färber wrote:
>> Specify the baudrate.
>>
>> Fixes: 26ca8b52d6e1 ("ARM: dts: add support for Turris Omnia")
>> Cc: Uwe Kleine-König <uwe@...ine-koenig.org>
>> Signed-off-by: Andreas Färber <afaerber@...e.de>
> 
> You said with plain &uart0 the kernel uses a wrong baud rate? That's
> strange. For me it works and I think it's the intended behaviour to
> dermine the baud rate setup by the bootloader and use this.

IIRC the 8250 driver defaults to 9600n8 if unspecified.

Kernel tested: 4.9.0-rc2-next-20161028-00010-g4fb44d9-dirty

Maybe you used some console= argument overriding it?

> I'd prefer it this way over hard coding the baud rate.
> 
>>  arch/arm/boot/dts/armada-385-turris-omnia.dts | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/arm/boot/dts/armada-385-turris-omnia.dts b/arch/arm/boot/dts/armada-385-turris-omnia.dts
>> index f53cb8b73610..2eff012287d4 100644
>> --- a/arch/arm/boot/dts/armada-385-turris-omnia.dts
>> +++ b/arch/arm/boot/dts/armada-385-turris-omnia.dts
>> @@ -52,7 +52,7 @@
>>  	compatible = "cznic,turris-omnia", "marvell,armada385", "marvell,armada380";
>>  
>>  	chosen {
>> -		stdout-path = &uart0;
>> +		stdout-path = "serial0:115200n8";
>>  	};
>>  
>>  	memory {
> 
> This has the downside to depend on the alias. Not sure this is
> considered modern. An alternative would be:
> 
> 	stdout-path = "/soc/internal-regs/serial@...00:115200n8";

Please don't unroll the path I'm trying to abstract elsewhere.

Like I said, the "serialX:115200n8" syntax is what all other Armada 38x
boards use:

git grep stdout-path -- arch/arm/boot/dts/ | grep armada-38
arch/arm/boot/dts/armada-385-db-ap.dts:		stdout-path = "serial1:115200n8";
arch/arm/boot/dts/armada-385-linksys.dtsi:		stdout-path =
"serial0:115200n8";
arch/arm/boot/dts/armada-388-clearfog.dts:		stdout-path =
"serial0:115200n8";
arch/arm/boot/dts/armada-388-db.dts:		stdout-path = "serial0:115200n8";
arch/arm/boot/dts/armada-388-gp.dts:		stdout-path = "serial0:115200n8";
arch/arm/boot/dts/armada-388-rd.dts:		stdout-path = "serial0:115200n8";

The alias is needed to reliably determine the tty device number and is
set "globally" in armada-38x.dtsi, so why is it a problem to rely on?

Regards,
Andreas

> 
> (maybe there even exists syntactic sugar to express this using &uart0?)

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