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

[WANG Xuerui]

On 2020/5/18 09:08, Tiezhu Yang wrote:

> 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@1fe001e0 {
> > > ÂÂÂÂÂÂÂÂ compatible = "ns16550a";
> > > ÂÂÂÂÂÂÂÂ reg = <0 0x1fe001e0 0x8>;
> > > ÂÂÂÂÂÂÂÂ clock-frequency = <33000000>;
> > > ÂÂÂÂÂÂÂÂ interrupt-parent = <&liointc>;
> > > ÂÂÂÂÂÂÂÂ interrupts = <10 IRQ_TYPE_LEVEL_HIGH>;
> > > ÂÂÂÂÂÂÂÂ 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:
> > >
> > > [ÂÂÂ 1.877745] printk: console [ttyS0] disabled
> > > [ÂÂÂ 1.881979] 1fe001e0.serial: ttyS0 at MMIO 0x1fe001e0 (irq = 16, 
> > > base_baud = 2062500) is a 16550A
> > > [ÂÂÂ 1.890838] printk: console [ttyS0] enabled
> > >
> > > And also, we can login normally from the serial console.
> > >
> > > Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
> > > ---
> > >
> > > Hi Jiaxun,
> > >
> > > Thank you very much for your suggestion.
> > >
> > > Â arch/mips/configs/loongson3_defconfig | 1 +
> > > Â 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
> > > Â CONFIG_SERIAL_8250_MANY_PORTS=y
> > > Â CONFIG_SERIAL_8250_SHARE_IRQ=y
> > > Â CONFIG_SERIAL_8250_RSA=y
> > > +CONFIG_SERIAL_OF_PLATFORM=y
> > > Â CONFIG_HW_RANDOM=y
> > > Â CONFIG_RAW_DRIVER=m
> > > Â 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.

One can always use their own config to build in whatever support they 
want. Only people blindly following defconfig are affected. That's why I 
think the original patch title is exaggerating.

> 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
> ÂÂÂÂÂÂÂ tristate "Devicetree based probing for 8250 ports"
>
> I will send v2 later.
No problem. Just make it clear that these are defconfig changes so 
people don't misunderstand, even if they're otherwise unfamiliar with 
the current state of things.
> Thanks,
> Tiezhu Yang