Hi,

On 04-11-16 13:30, Paul Burton wrote:

Hi Hans,

On Friday, 4 November 2016 13:11:34 GMT Hans de Goede wrote:

quoted

Hi All,

While booting 4.9-rc# for the first time on an Allwinner A33 tablet,
I noticed that after u-boot the LCD display stayed black. It turns out
that there was an issue which caused X to never get up, and all kernel
(and other startup) messages prior to that only went to ttyS0 which
consists of 2 tiny testpads on the PCB with this tablet.

The same issue will also happen on any ARM boards which have a HDMI or
composite video output and which use a stdout-path pointing to their
serial console. I think this will e.g. also impact the Raspberry Pi,
I know for certain that this will impact the 99 different Allwinnner
boards currently supported by mainline u-boot + the mainline kernel.

This is a behavior changes from previous kernels and I consider this
a regression. Thus I propose to revert the commit in question, for more
info here is a partial copy of the commit message of the proposed revert:

The reverted commit changes existing behavior on which many ARM boards
rely. Many ARM small-board-computers, like e.g. the Raspberry Pi have
both a video output and a serial console. Depending on whether the user
is using the device as a more regular computer; or as a headless device
we need to have the console on either one or the other.

Many users rely on the kernel behavior of the console being present on
both outputs, before the reverted commit the console setup with no
console= kernel arguments on an ARM board which sets stdout-path in dt
would look like this:

[root@localhost ~]# cat /proc/consoles
ttyS0                -W- (EC p a)    4:64
tty0                 -WU (E  p  )    4:1

Where as after the reverted commit, it looks like this:

[root@localhost ~]# cat /proc/consoles
ttyS0                -W- (EC p a)    4:64

This commit reverts commit 05fd007e4629 ("console: don't prefer first
registered if DT specifies stdout-path") restoring the original behavior.

Regards,

Hans

Ugh... so the devices you're talking about rely upon set stdout-path in their
device tree but effectively rely upon us ignoring it?

No they rely on the kernel using stdout-path as an extra console while keeping
tty0 as console, not ignoring it. This how stdout-path has always worked
(at least as long as the Allwinner boards have used it, which has been
  2 - 3 years now).

If you want only the console specified by stdout-path you can get this by
specifying it with console=... on the kernel cmdline.

If that's the case then I guess reverting is probably the best option, but it
does restore us to a position where we honor stdout-path for earlycon & then
essentially ignore it for the proper kernel console. That seems pretty bust to
me...

We do not ignore it, we use both the tty pointed to by stdout-path and tty0.

Regards,

Hans
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