[PATCH] bootm: Fix Linux silent console on newer kernels

[Tom Rini]

On Thu, May 19, 2022 at 06:26:05PM -0400, Sean Anderson wrote:

> Linux determines its console based on several sources:
> 
> 1. the console command line parameter
> 2. device tree (e.g. /chosen/stdout-path)
> 3. various other board- and arch-specific sources
> 
> If the console parameter specifies a real console (e.g. ttyS0) then that is
> used as /dev/console. However, if it does not specify a real console (e.g.
> ttyDoesntExist) then *nothing* will be used as /dev/console.
> Reading/writing it will return ENODEV. Additionally, no other source will
> be used as a console source.
> 
> Linux commit ab4af56ae250 ("printk/console: Allow to disable console output
> by using console="" or console=null") recently changed the semantics of the
> parameter. Previously, specifying console="" would be treated like
> specifying some other bad console. This commit changed things so that it
> added /dev/ttynull as a console (if available).  However, it also allows
> for other console sources. If the device tree specifies a console (such as
> if U-Boot and Linux share a device tree), then it will be used in addition
> to /dev/ttynull. This can result in a non-silent console.
> 
> To avoid this, explicitly set ttynull as the console. This will disable
> other console sources. If CONFIG_NULL_TTY is disabled, then this will have
> the same behavior as in the past (no output, and writing /dev/console
> returns ENODEV).
> 
> [1] and [2] have additional background on this kernel change.
> 
> [1] https://lore.kernel.org/all/20201006025935.GA597@jagdpanzerIV.localdomain/
> [2] https://lore.kernel.org/all/20201111135450.11214-1-pmladek@suse.com/
> 
> Signed-off-by: Sean Anderson <sean.anderson at seco.com>

Applied to u-boot/next, thanks!

-- 
Tom
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