linux-kernel - Re: [PATCH] MIPS: Loongson: Add support for serial console

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Date:   Mon, 18 May 2020 09:08:14 +0800
From:   Tiezhu Yang <yangtiezhu@...ngson.cn>
To:     WANG Xuerui <kernel@...0n.name>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Huacai Chen <chenhc@...ote.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>
Cc:     linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xuefeng Li <lixuefeng@...ngson.cn>
Subject: Re: [PATCH] MIPS: Loongson: Add support for serial console

On 05/16/2020 07:09 PM, WANG Xuerui wrote:
> On 5/16/20 3:03 PM, Tiezhu Yang wrote:
>
>> After commit 87fcfa7b7fe6 ("MIPS: Loongson64: Add generic dts"),
>> there already exists the node and property of Loongson CPU UART0
>> in loongson3-package.dtsi:
>>
>> cpu_uart0: serial@...001e0 {
>>          compatible = "ns16550a";
>>          reg = <0 0x1fe001e0 0x8>;
>>          clock-frequency = <33000000>;
>>          interrupt-parent = <&liointc>;
>>          interrupts = <10 IRQ_TYPE_LEVEL_HIGH>;
>>          no-loopback-test;
>> };
>>
>> In order to support for serial console on the Loongson platform,
>> add CONFIG_SERIAL_OF_PLATFORM=y to loongson3_defconfig.
>>
>> With this patch, we can see the following boot message:
>>
>> [    1.877745] printk: console [ttyS0] disabled
>> [    1.881979] 1fe001e0.serial: ttyS0 at MMIO 0x1fe001e0 (irq = 16, 
>> base_baud = 2062500) is a 16550A
>> [    1.890838] printk: console [ttyS0] enabled
>>
>> And also, we can login normally from the serial console.
>>
>> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
>> ---
>>
>> Hi Jiaxun,
>>
>> Thank you very much for your suggestion.
>>
>>   arch/mips/configs/loongson3_defconfig | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/arch/mips/configs/loongson3_defconfig 
>> b/arch/mips/configs/loongson3_defconfig
>> index 6768c16..cd95f08 100644
>> --- a/arch/mips/configs/loongson3_defconfig
>> +++ b/arch/mips/configs/loongson3_defconfig
>> @@ -217,6 +217,7 @@ CONFIG_SERIAL_8250_EXTENDED=y
>>   CONFIG_SERIAL_8250_MANY_PORTS=y
>>   CONFIG_SERIAL_8250_SHARE_IRQ=y
>>   CONFIG_SERIAL_8250_RSA=y
>> +CONFIG_SERIAL_OF_PLATFORM=y
>>   CONFIG_HW_RANDOM=y
>>   CONFIG_RAW_DRIVER=m
>>   CONFIG_I2C_CHARDEV=y
>
> Hi,
>
> The patch title is again exaggerating things. This is a defconfig 
> change, so please refer to `git log` output of `arch/mips/configs` and 
> use something like "MIPS: Loongson: loongson3_defconfig: enable serial 
> console" or "MIPS: Loongson: enable serial console in defconfig". The 
> current title reads as if Loongson kernels never were able to use a 
> serial console in the past.

Hi Xuerui,

Thanks for your suggestion.

We can not use the serial console without this patch,
so I use the current patch subject.

Anyway, let me modify the patch subject to make it more accurate,
I think the following is better:
"MIPS: Loongson: Enable devicetree based probing for 8250 ports"

drivers/tty/serial/8250/Kconfig:
config SERIAL_OF_PLATFORM
         tristate "Devicetree based probing for 8250 ports"

I will send v2 later.

Thanks,
Tiezhu Yang