On Thu, May 19, 2022 at 06:26:05PM -0400, Sean Anderson wrote:
Linux determines its console based on several sources:
- the console command line parameter
- device tree (e.g. /chosen/stdout-path)
- 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@seco.com
Applied to u-boot/next, thanks!