linux-kernel - RE: [PATCH] arm64: dts: exynos: Add minimal bootargs

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Date:   Sun, 5 Jul 2020 07:09:14 +0530
From:   "Alim Akhtar" <alim.akhtar@...sung.com>
To:     "'Krzysztof Kozlowski'" <krzk@...nel.org>
Cc:     <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-samsung-soc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <robh+dt@...nel.org>
Subject: RE: [PATCH] arm64: dts: exynos: Add minimal bootargs

Hi Krzysztof,

> > > @@ -24,6 +24,7 @@
> > >
> > >  	chosen {
> > >  		stdout-path = &serial_2;
> > > +		bootargs = "earlycon=exynos4210,0x14c30000
> > > console=ttySAC0,115200n8";
> 
> Hi,
> 
> The console is already chosen by stdout-path and earlycon would use it as well,
> so no need for the address. It should be just "earlycon" if you want to enable it
> unconditionally.
> 
Indeed only "earlycon" will do here. Thanks for point this out.

> Also, why did you use different serial for console?
> 
Once UART driver gets probed then console changes to ttySAC0. In case I am using stdout-path only,
after bootconsole is disabled, kernel logs re-start printing from beginning (which might be expected behaviour?)

[    0.012416] printk: console [tty0] enabled
[    0.016491] printk: bootconsole [exynos4210] disabled
[    0.000000] Booting Linux on physical CPU 0x0000000000 [0x410fd032]
[    0.000000] Linux version 5.8.0-rc3-next-20200703-00008-g4af626444f4a-dirty (alim@...m) (aarch64-linux-gnu-gcc (Linaro GCC 7.4-2019.02) 7.4.1 20181213 [l0
[    0.000000] Machine model: Samsung Exynos7 Espresso board based on Exynos7

> However the question is, are you sure you want earlycon on every, including
> successful boot? On most of the boards we do not enable by default. If
> developer needs, he can choose it for example via U-Boot "setenv opts
> earlycon".
> 
Using U-Boot is not the case always, any bootload can be used to boot the Linux, currently I am Coreboot.
And 'earlycon' is not setup by default.
As Espresson board is development board, IMO it is ok to keep it enable all the time, this helps in quickly knowing what going on incase boot fails early.
Let me know if it is ok to keep " console=ttySAC0,115200n8" or shell I just re-spin with only 'earlycon'? or any other suggestion?

Thanks!

> However it's a development kit so it could be enabled on default...
> 
> Best regards,
> Krzysztof
> 
> > >  	};
> > >
> > >  	memory@...00000 {
> > >
> > > base-commit: 9e50b94b3eb0d859a2586b5a40d7fd6e5afd9210
> > > --
> > > 2.17.1
> >
> >