linux-kernel - Re: [PATCH 1/1] tty/serial: to support 8250 earlycon can be enabled independently

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Date:	Tue, 17 May 2016 14:11:47 +0800
From:	"Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:	Peter Hurley <peter@...leysoftware.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>,
	linux-serial <linux-serial@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
CC:	Zefan Li <lizefan@...wei.com>, Xinwei Hu <huxinwei@...wei.com>,
	"Tianhong Ding" <dingtianhong@...wei.com>,
	Hanjun Guo <guohanjun@...wei.com>,
	"Kefeng Wang" <wangkefeng.wang@...wei.com>
Subject: Re: [PATCH 1/1] tty/serial: to support 8250 earlycon can be enabled
 independently



On 2016/5/16 23:40, Peter Hurley wrote:
> On 05/16/2016 04:35 AM, Zhen Lei wrote:
>> Sometimes, we may only use SSH to login, and build 8250 uart driver as a
>> ko(insmod if needed). But the earlycon may still be necessary, because
>> the kernel boot process may take a long time. It's not good to display
>> nothing but ask people to wait patiently.
> 
> I'm confused; you want the possibility of earlycon but _not_ a normal
> serial console?
Our downstream customers want add some private functions into 8250.ko. So that, we can not pre-build the 8250 driver into Image.

> 
> This configuration is unsafe because nothing prevents the 8250 driver
> and 8250 earlycon from concurrently accessing the hardware.
earlycon is a boot console, it will be disabled in printk_late_init(suppose we have not set keep_bootcon).

> 
> 
>> In addition, the 8250.ko can not be worked if we have not opened any
>> other serial drivers, because SERIAL_CORE would not be selected.
> 
> I don't understand what this means.

Before I opened CONFIG_SERIAL_AMBA_PL011_CONSOLE(only built 8250 as a module, this case can not be worked):
CONFIG_SERIAL_CORE=m

After I opened CONFIG_SERIAL_AMBA_PL011_CONSOLE:
CONFIG_SERIAL_EARLYCON=y
CONFIG_SERIAL_AMBA_PL011=y
CONFIG_SERIAL_AMBA_PL011_CONSOLE=y
CONFIG_SERIAL_CORE=y
CONFIG_SERIAL_CORE_CONSOLE=y

> 
> Regards,
> Peter Hurley
> 
> 
>> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
>> ---
>>  drivers/tty/serial/8250/Kconfig  | 9 +++++++--
>>  drivers/tty/serial/8250/Makefile | 1 -
>>  drivers/tty/serial/Makefile      | 1 +
>>  3 files changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/tty/serial/8250/Kconfig b/drivers/tty/serial/8250/Kconfig
>> index 4d7cb9c..2992f0a 100644
>> --- a/drivers/tty/serial/8250/Kconfig
>> +++ b/drivers/tty/serial/8250/Kconfig
>> @@ -3,6 +3,12 @@
>>  # you somehow have an implicit or explicit dependency on SERIAL_8250.
>>  #
>>
>> +config SERIAL_8250_EARLYCON
>> +	bool "Early console using 8250"
>> +	select SERIAL_CORE
>> +	select SERIAL_CORE_CONSOLE
>> +	select SERIAL_EARLYCON
>> +
>>  config SERIAL_8250
>>  	tristate "8250/16550 and compatible serial support"
>>  	select SERIAL_CORE
>> @@ -60,8 +66,7 @@ config SERIAL_8250_PNP
>>  config SERIAL_8250_CONSOLE
>>  	bool "Console on 8250/16550 and compatible serial port"
>>  	depends on SERIAL_8250=y
>> -	select SERIAL_CORE_CONSOLE
>> -	select SERIAL_EARLYCON
>> +	select SERIAL_8250_EARLYCON
>>  	---help---
>>  	  If you say Y here, it will be possible to use a serial port as the
>>  	  system console (the system console is the device which receives all
>> diff --git a/drivers/tty/serial/8250/Makefile b/drivers/tty/serial/8250/Makefile
>> index c9a2d6e..1f24c74 100644
>> --- a/drivers/tty/serial/8250/Makefile
>> +++ b/drivers/tty/serial/8250/Makefile
>> @@ -13,7 +13,6 @@ obj-$(CONFIG_SERIAL_8250_HP300)		+= 8250_hp300.o
>>  obj-$(CONFIG_SERIAL_8250_CS)		+= serial_cs.o
>>  obj-$(CONFIG_SERIAL_8250_ACORN)		+= 8250_acorn.o
>>  obj-$(CONFIG_SERIAL_8250_BCM2835AUX)	+= 8250_bcm2835aux.o
>> -obj-$(CONFIG_SERIAL_8250_CONSOLE)	+= 8250_early.o
>>  obj-$(CONFIG_SERIAL_8250_FOURPORT)	+= 8250_fourport.o
>>  obj-$(CONFIG_SERIAL_8250_ACCENT)	+= 8250_accent.o
>>  obj-$(CONFIG_SERIAL_8250_BOCA)		+= 8250_boca.o
>> diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
>> index 8c261ad..cd84181 100644
>> --- a/drivers/tty/serial/Makefile
>> +++ b/drivers/tty/serial/Makefile
>> @@ -19,6 +19,7 @@ obj-$(CONFIG_SERIAL_SUNSAB) += sunsab.o
>>
>>  # Now bring in any enabled 8250/16450/16550 type drivers.
>>  obj-$(CONFIG_SERIAL_8250) += 8250/
>> +obj-$(CONFIG_SERIAL_8250_EARLYCON) += 8250/8250_early.o
>>
>>  obj-$(CONFIG_SERIAL_AMBA_PL010) += amba-pl010.o
>>  obj-$(CONFIG_SERIAL_AMBA_PL011) += amba-pl011.o
>> --
>> 2.5.0
>>
>>
>> --
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>>
> 
> 
> .
>