Hi,

On 07-11-16 18:16, Paul Burton wrote:

Hi Hans,

On Sunday, 6 November 2016 11:54:35 GMT Hans de Goede wrote:

quoted

quoted

What I see in my systems, and what 05fd007e4629 ("console: don't prefer
first registered if DT specifies stdout-path") addressed, is that if
there are for example 2 UARTs uart0 & uart1 that are probed in that order
and stdout-path indicates that we should use uart1 we wind up essentially
ignoring it because>
the ordering of the relevant calls goes:
  - of_console_check() for uart0
  - add_preferred_console() for uart0
  - register_console() for uart0
  - of_console_check() for uart1
  - add_preferred_console() for uart1
  - register_console() for uart1

Since of_check_console() doesn't get called for uart1 until after uart0
has
been probed, we don't add an entry for it to the console_cmdline array
until after register_console() has already decided to enable uart0
because preferred_console == -1.

I'm not the only one seeing this oddity either, for example see the
discussion on this patch:

https://patchwork.kernel.org/patch/9263753/

By simply reverting my patch you restore us to a position where so far as
I
can see we simply do not honor stdout-path for the real kernel console.

As said before, we do still honor it, but in your probe example we also get
a (second) serial console on uart0, where as you only want one on uart1.

...but don't we only support one console per type of device? That's what
Documentation/serial-console.txt says anyway, which means having a console on
both uart0 & uart1 does not work. I could live with having console output on
an extra UART, but that's not what I was seeing when I wrote this patch.

Ah yes, you're probably right about that.

quoted

So I see a few possible solutions here:

1) Do a new version of your patch which changes the  "&&
!of_specified_console" check to "&& (newcon == tty0 ||
!of_specified_console)", then we would still always register tty0 (as long
as it gets registered first, just like now) and we would not register uart0
in your above example, note the "newcon == tty0" check in my example is
pseudo-code. I would be happy to try out such a patch

2) Add a new dt property to enable the new behavior you seek

I'm myself tending towards 1 as a better solution: treat tty0 special,
because some existing setups rely on it always being registered as a
console even if stdout-path is specified and otherwise always honor
stdout-path.

Regards,

Hans

That does feel a little hack-ish to me though... I don't like the reliance on
probe ordering, nor special casing tty0 in general.

Given that we've just got a "me too" reply from the ppc side of things,
it seems that in reality people have been relying on probe ordering here
for a long time now. IMHO tty0 is special, so it does make sense that it
always gets probed first (*) and it does make sense to handle it special.

*) Even though that seems to be more how things work (an implicit thing)
rather then explicit.

In any case I don't think I have the time to unpick all this at the moment, so
I suggest we go ahead with your revert for now & I'll revisit the system I was
working on when I find the time.

Ok.

Regards,

Hans