Date:	Fri, 29 Aug 2014 09:56:45 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Sahara <kpark3469@...il.com>,
	Thierry Reding <thierry.reding@...il.com>
CC:	akpm@...ux-foundation.org, keun-o.park@...driver.com,
	hpa@...or.com, rafael.j.wysocki@...el.com, peterz@...radead.org,
	rusty@...tcorp.com.au, kirill.shutemov@...ux.intel.com,
	oleg@...hat.com, prarit@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] earlyprintk: re-enable earlyprintk calling early_param

On 08/28/2014 11:28 PM, Sahara wrote:
>
>
> On Wed, 27 Aug 2014, Thierry Reding wrote:
>
>> On Thu, Aug 14, 2014 at 07:13:36PM +0900, kpark3469@...il.com wrote:
>>> From: Sahara <keun-o.park@...driver.com>
>>>
>>> Although there are many obs_kernel_param and its names are
>>> earlyprintk and also EARLY_PRINTK is also enabled, we could not
>>> see the early_printk output properly until now. This patch
>>> considers earlycon as well as earlyprintk.
>>>
>>> Signed-off-by: Sahara <keun-o.park@...driver.com>
>>> ---
>>>  init/main.c |    3 ++-
>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/init/main.c b/init/main.c
>>> index bb1aed9..235d248 100644
>>> --- a/init/main.c
>>> +++ b/init/main.c
>>> @@ -426,7 +426,8 @@ static int __init do_early_param(char *param, char
> *val, const char *unused)
>>>      for (p = __setup_start; p < __setup_end; p++) {
>>>          if ((p->early && parameq(param, p->str)) ||
>>>              (strcmp(param, "console") == 0 &&
>>> -             strcmp(p->str, "earlycon") == 0)
>>> +             ((strcmp(p->str, "earlycon") == 0) ||
>>> +             (strcmp(p->str, "earlyprintk") == 0)))
>>>          ) {
>>>              if (p->setup_func(val) != 0)
>>>                  pr_warn("Malformed early option '%s'\n",
> param);
>>
>> It seems like this patch causes the following warning for me during
>> boot:
>>
>> [    0.000000] Booting Linux on physical CPU 0x0
>> [    0.000000] Initializing cgroup subsys cpu
>> [    0.000000] Initializing cgroup subsys cpuacct
>> [    0.000000] Linux version 3.17.0-rc2-next-20140827
> (thierry.reding@...o) (gcc version 4.9.0 (GCC) ) #18 SMP PREEMPT Wed Aug
> 27 17:08:12 CEST 2014
>> [    0.000000] CPU: ARMv7 Processor [413fc0f3] revision 3 (ARMv7),
> cr=10c5387d
>> [    0.000000] CPU: PIPT / VIPT nonaliasing data cache, PIPT instruction
> cache
>> [    0.000000] Machine model: NVIDIA Tegra124 Jetson TK1
>> [    0.000000] bootconsole [earlycon0] enabled
>> [    0.000000] debug: ignoring loglevel setting.
>> [    0.000000] ------------[ cut here ]------------
>> [    0.000000] WARNING: CPU: 0 PID: 0 at
> /home/thierry.reding/src/kernel/linux-work.git/kernel/printk/printk.c:2402
> register_console+0x60/0x37c()
>> [    0.000000] console 'earlycon0' already registered
>> [    0.000000] Modules linked in:
>> [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted
> 3.17.0-rc2-next-20140827 #18
>> [    0.000000] [<c0015fec>] (unwind_backtrace) from [<c0011aac>]
> (show_stack+0x10/0x14)
>> [    0.000000] [<c0011aac>] (show_stack) from [<c062b700>]
> (dump_stack+0x98/0xd8)
>> [    0.000000] [<c062b700>] (dump_stack) from [<c0025ba0>]
> (warn_slowpath_common+0x70/0x8c)
>> [    0.000000] [<c0025ba0>] (warn_slowpath_common) from [<c0025bec>]
> (warn_slowpath_fmt+0x30/0x40)
>> [    0.000000] [<c0025bec>] (warn_slowpath_fmt) from [<c00639b8>]
> (register_console+0x60/0x37c)
>> [    0.000000] [<c00639b8>] (register_console) from [<c0883870>]
> (setup_early_printk+0x20/0x28)
>> [    0.000000] [<c0883870>] (setup_early_printk) from [<c087f43c>]
> (do_early_param+0x6c/0xd0)
>> [    0.000000] [<c087f43c>] (do_early_param) from [<c003cba0>]
> (parse_args+0x238/0x3d0)
>> [    0.000000] [<c003cba0>] (parse_args) from [<c087f814>]
> (parse_early_options+0x38/0x40)
>> [    0.000000] [<c087f814>] (parse_early_options) from [<c087f84c>]
> (parse_early_param+0x30/0x40)
>> [    0.000000] [<c087f84c>] (parse_early_param) from [<c088206c>]
> (setup_arch+0x4b4/0x974)
>> [    0.000000] [<c088206c>] (setup_arch) from [<c087f8f8>]
> (start_kernel+0x98/0x3a8)
>> [    0.000000] [<c087f8f8>] (start_kernel) from [<80008074>]
> (0x80008074)
>> [    0.000000] ---[ end trace cb88537fdc8fa200 ]---
>> [    0.000000] cma: Reserved 128 MiB at a7800000
>> [    0.000000] Memory policy: Data cache writealloc
>> [    0.000000] On node 0 totalpages: 524032
>> [    0.000000] free_area_init_node: node 0, pgdat c091cc00, node_mem_map
> e67b7000
>> [    0.000000]   Normal zone: 1520 pages used for memmap
>> [    0.000000]   Normal zone: 0 pages reserved
>> [    0.000000]   Normal zone: 194560 pages, LIFO batch:31
>> [    0.000000]   HighMem zone: 2574 pages used for memmap
>> [    0.000000]   HighMem zone: 329472 pages, LIFO batch:31
>> [    0.000000] PERCPU: Embedded 8 pages/cpu @e6767000 s8832 r8192 d15744
> u32768
>> [    0.000000] pcpu-alloc: s8832 r8192 d15744 u32768 alloc=8*4096
>> [    0.000000] pcpu-alloc: [0] 0 [0] 1 [0] 2 [0] 3
>> [    0.000000] Built 1 zonelists in Zone order, mobility grouping on.
> Total pages: 522512
>> [    0.000000] Kernel command line: console=ttyS0,115200n8
> ignore_loglevel rootwait ro earlyprintk ip=:::::eth0:dhcp root=/dev/nfs
> nfsroot=192.168.69.100:/srv/nfs/tegra124 drm.debug=0xf cma=128M
>>
>> Reverting the patch eliminates the warning. earlyprintk does work fine
>> for me without this patch.
>>
>> Thierry
>
>
> This warning message is caused by specifying 'earlyprintk' in
> your command line args. Same problem may happen if you specify 'earlycon'
> in your command line args and enable CONFIG_SERIAL_EARLYCON with
> the current code without this patch. I think it's appropriate result
> letting a developer know that both ways of using earlyprintk are enabled.
> With current code, although a developer enables CONFIG_EARLY_PRINTK and
> has "console=" arg in command line args, he/she should specify the
> 'earlyprintk' in command line args also to see early_printk() outputs.
> With this patch, simply enabling CONFIG_EARLY_PRINTK and having 'console='
> line make you be able to the early_printk().
>
> Nonetheless I want to retract this patch. It's good for ARM, but not good
> for other architectures such as x86. And, because CONFIG_EARLY_PRINTK is
> depending on DEBUG_LL in ARM, making a relation with "console=" is absurd.
> (see strcmp(param, "console") == 0 && strcmp(p->str, "earlyprintk") == 0)

Even on ARM, this patch feels like the wrong thing. After all, I can 
build a DEBUG_LL enabled multi-platform kernel, and boot it on a bunch 
of different SoCs. However, earlyprintk will only work on one (or zero) 
of those SoCs, and hence shouldn't automatically enable itself; 
specifically requesting activation using the earlyprintk kernel 
command-line parameter is the correct approach.
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