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

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Date:   Sun, 5 Jul 2020 20:09:44 +0200
From:   'Krzysztof Kozlowski' <krzk@...nel.org>
To:     Alim Akhtar <alim.akhtar@...sung.com>
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

On Sun, Jul 05, 2020 at 07:09:14AM +0530, Alim Akhtar wrote:
> Hi Krzysztof,
> > 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
> 

No, this is not desired. The fix for it should not be redefining the
console to wrong argument.

For example on Odroid MC1 this problem does not exist:

[    0.000000] earlycon: exynos4210 at MMIO 0x12c20000 (options '115200n8')
[    0.000000] printk: bootconsole [exynos4210] enabled
[    3.111883] printk: console [ttySAC2] enabled
[    3.111883] printk: console [ttySAC2] enabled
[    3.120102] printk: bootconsole [exynos4210] disabled
[    3.120102] printk: bootconsole [exynos4210] disabled


but your console for some reason is tty0... why? Is your console
ttySAC2? Maybe it is the effect of alias:
serial0 = &serial_2;

> > 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?

It should be just earlycon.

Best regards,
Krzysztof