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

From: Lyra Zhang
Date: Tue Oct 14 2014 - 23:17:26 EST

Hi, Arnd

2014-09-29 21:47 GMT+08:00 Arnd Bergmann <arnd@xxxxxxxx>:
> On Monday 29 September 2014 20:04:49 zhang.lyra@xxxxxxxxx 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@70000000";

uart0: serial@70000000 {

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?

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