linux-kernel - Re: [PATCH 2/6] arm64: Add DTS support for Spreadtrum's Shark64 SoC

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Date:	Wed, 15 Oct 2014 11:17:07 +0800
From:	Lyra Zhang <zhang.lyra@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	catalin.marinas@....com, gregkh@...uxfoundation.org,
	ijc+devicetree@...lion.org.uk, jslaby@...e.cz,
	Kumar Gala <galak@...eaurora.org>,
	Mark Brown <broonie@...aro.org>, mark.rutland@....com,
	m-karicheri2@...com, pawel.moll@....com,
	Ramkumar Ramachandra <artagnon@...il.com>, rrichter@...ium.com,
	robh+dt@...nel.org, will.deacon@....com,
	Orson Zhai <orsonzhai@...il.com>, geng.ren@...eadtrum.com,
	"zhizhou.zhang" <zhizhou.zhang@...eadtrum.com>,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	"chunyan.zhang" <chunyan.zhang@...eadtrum.com>
Subject: Re: [PATCH 2/6] arm64: Add DTS support for Spreadtrum's Shark64 SoC

Hi, Arnd

2014-09-29 21:47 GMT+08:00 Arnd Bergmann <arnd@...db.de>:
> On Monday 29 September 2014 20:04:49 zhang.lyra@...il.com wrote:
>> +
>> +/memreserve/ 0x80000000 0x00010000;
>
> Maybe add a comment explaining why it is reserved?
>
>> +     chosen {
>> +             bootargs = "earlycon=serial_sprd,0x70000000";
>> +      };
>
> Just remove this for now, the command line should really be set by the
> boot loader, not hardcoded in the dts file.
>
> IIRC, the earlycon=... syntax is not recommended on DT based systems,
> better use the "stdout-path" syntax instead.
>

I have tried to use  "stdout-path" instead of "bootargs= "earlycon=
..." like below :

/ {
     ...

     chosen {
             stdout-path = "/serial@...00000";
      };

     uart0: serial@...00000 {
             status="okay";
     };
      ...
};

But then there is nothing output information on serial console.(I have
been testing in Fast Model)

I saw the below code in init/main.c

/* Check for early params. */
static int __init do_early_param(char *param, char *val, const char *unused)
{
const struct obs_kernel_param *p;

for (p = __setup_start; p < __setup_end; p++) {
if ((p->early && parameq(param, p->str)) ||
   (strcmp(param, "console") == 0 &&
    strcmp(p->str, "earlycon") == 0)
) {
if (p->setup_func(val) != 0)
pr_warn("Malformed early option '%s'\n", param);
}
}
/* We accept everything at this stage. */
return 0;
}

And I saw a patch from Grant Likely, he had a comment in it :
"If the devicetree specifies a serial port as a stdout device, then the
kernel can use it as the default console if nothing else was selected on
the command line. For any serial port that uses the uart_add_one_port()
feature, the uart_add_one_port() has all the information needed to
automatically enable the console device, which is what this patch does."

So, I guess that the reason why I can't see any output information on
console after using "stdout-path" instead of "earlycon" is that I
haven't a driver of Spreadtrum's serial, and dose not use  the
uart_add_one_port() feature.

I don't know is correct what I guess.

Could you give me some suggestions to solve this problem?

Thanks,
Chunyan
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