From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hans de Goede Subject: Re: [REGRESSION] "console: don't prefer first registered if DT specifies stdout-path" breaks console on video outputs of various ARM boards Date: Tue, 8 Nov 2016 10:12:05 +0100 Message-ID: References: <20161104121135.4780-1-hdegoede@redhat.com> <1573891.u0IFOelkNI@np-p-burton> <3421375.fR4RSn7eD9@np-p-burton> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <3421375.fR4RSn7eD9@np-p-burton> Sender: linux-kernel-owner@vger.kernel.org To: Paul Burton Cc: Linus Torvalds , Andrew Morton , Rob Herring , Frank Rowand , Thorsten Leemhuis , Greg Kroah-Hartman , Tejun Heo , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: devicetree@vger.kernel.org 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: >>> 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. >> 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