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Subject: Re: [PATCH] MIPS: Loongson: Add support for serial console
To:     Tiezhu Yang <yangtiezhu@loongson.cn>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Huacai Chen <chenhc@lemote.com>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc:     linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org,
        Xuefeng Li <lixuefeng@loongson.cn>
References: <1589612588-29196-1-git-send-email-yangtiezhu@loongson.cn>
From:   WANG Xuerui <kernel@xen0n.name>
Message-ID: <5aadf1a7-51c7-453e-beaa-3df6ceca5354@xen0n.name>
Date:   Sat, 16 May 2020 19:09:11 +0800
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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@1fe001e0 {
>          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@loongson.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.