linux-kernel - Re: [PATCH 3/3] ARM: dts: Define stdout-path property for Spring board

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Date:	Wed, 18 Mar 2015 00:29:12 +0900
From:	Kukjin Kim <kgene@...nel.org>
To:	Javier Martinez Canillas <javier@...hile0.org>
CC:	Andreas Färber <afaerber@...e.de>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	Kukjin Kim <kgene@...nel.org>, Olof Johansson <olof@...om.net>,
	Doug Anderson <dianders@...omium.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] ARM: dts: Define stdout-path property for Spring
 board

On 03/16/15 20:28, Javier Martinez Canillas wrote:
> Hello Andreas,
> 
Hi,

>>> index f02775487cd4..b9ec763a5602 100644
>>> --- a/arch/arm/boot/dts/exynos5250-spring.dts
>>> +++ b/arch/arm/boot/dts/exynos5250-spring.dts
>>> @@ -25,6 +25,7 @@
>>>
>>>       chosen {
>>>               bootargs = "console=tty1";
>>> +             stdout-path = "serial3:115200n8";
>>
>> Is this a guess or did you verify that against some schematics?
>>
> 
> I don't have access to the Spring schematics but it is based on what
> is defined in the vendor u-boot for Spring [0].
> 
> There isn't a Spring specific configuration file but only a
> chromeos_daisy.h which is shared by Snow, Spring and Kate (not yet in
> mainline):
> 
> #define CONFIG_DIRECT_BOOTARGS \
> "console=ttySAC3," STRINGIFY(CONFIG_BAUDRATE) " debug earlyprintk"
> 
> So I assumed that all daisy-based Chromebooks use the same UART for debug.
> 
>>>       };
>>>
>>>       gpio-keys {
>>
>> Assuming that bootargs still work,
>>
> 
> Yes, the semantics are not changed. The std-out property is only used
> as a default if no console= parameter is passed so if you already are
> passing one in your bootloader or using the one defined in the /chosen
> bootargs by enabling CONFIG_ARM_ATAG_DTB_COMPAT_CMDLINE_EXTEND, that
> will be used instead of std-out.
> 
>> Reviewed-by: Andreas Färber <afaerber@...e.de>
>>
>> I do wonder why this mechanism could not point to the same location as
>> bootargs? ("dp-controller"?) The device does not even have screws for
> 
> I did wonder the same indeed but I don't know if you can use a display
> as std-out or only works for serial consoles.
> 
>> opening it, so accessing the serial port is highly theoretical.
>>
> 
> I see, in that case I think we could just drop this patch if is not
> possible to have a serial console even with some soldering like is the
> case in Snow, Peach Pit and Peach Pi.
> 
I've applied this whole series so if you guys find any problem on this,
please let me know ;)

Thanks,
Kukjin
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