Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161014AbbFENBd (ORCPT ); Fri, 5 Jun 2015 09:01:33 -0400 Received: from smtprelay.synopsys.com ([198.182.60.111]:32833 "EHLO smtprelay.synopsys.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1751210AbbFENB3 convert rfc822-to-8bit (ORCPT ); Fri, 5 Jun 2015 09:01:29 -0400 From: Vineet Gupta To: "linux-serial@vger.kernel.org" , "Arnd Bergmann" , Alexey Brodkin CC: "linux-serial@vger.kernel.org" , "linux-arch@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "arc-linux-dev@synopsys.com" , "devicetree@vger.kernel.org" , Rob Herring , Peter Hurley , "robh+dt@kernel.org" Subject: console setting via stdout-path vs console=xxx (was Re: [PATCH 2/4] ARC: [axs101] support early 8250 uart) Thread-Topic: console setting via stdout-path vs console=xxx (was Re: [PATCH 2/4] ARC: [axs101] support early 8250 uart) Thread-Index: AQHQn4+5hbHxh5TEOkyel6ORXQZYFQ== Date: Fri, 5 Jun 2015 13:01:23 +0000 Message-ID: References: <1431607724-9142-1-git-send-email-abrodkin@synopsys.com> <1431607724-9142-3-git-send-email-abrodkin@synopsys.com> <2836384.o6ec7X8zDk@wuerfel> <55712D5B.6090302@synopsys.com> Accept-Language: en-US, en-IN Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.12.197.3] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2559 Lines: 62 On Friday 05 June 2015 10:32 AM, Vineet Gupta wrote: > On Thursday 14 May 2015 06:34 PM, Vineet Gupta wrote: >> > On Thursday 14 May 2015 06:23 PM, Arnd Bergmann wrote: >> > >> > On Thursday 14 May 2015 15:48:42 Alexey Brodkin wrote: >> > >> > >>>> >> > >>>> >> > chosen { >>>> >> > - bootargs = "console=tty0 console=ttyS3,115200n8 consoleblank=0"; >>>> >> > + bootargs = "earlycon=uart8250,mmio32,0xe0022000,115200n8 console=tty0 console=ttyS3,115200n8 consoleblank=0"; >>>> >> > }; >>>> >> > }; >>>> >> > >> > >> > When you do earlycon with DT, better use a 'stdout-path' property that points >> > to the device, and just put 'earlycon' without arguments on the command line. >> > >> > Arnd >> > >> > >> > Sure ! I tried that once (3.16) and even the dts patch got merged but had to be reverted out ! >> > >> > 2014-07-27 22524b02b17b Revert "ARC: [arcfpga] stdout-path now suffices for earlycon/console" >> > >> > Let me see if that works again since serial land has seen some significant churn in recent times >> > >> > Thx for pointing this out ! > so specifying console with stdout-path works for me, > > - bootargs = "earlycon=uart8250,mmio32,0xf0000000,115200n8 console=tty0 > console=ttyS0,115200n8 consoleblank=0 debug"; > + bootargs = "earlycon=uart8250,mmio32,0xf0000000,115200n8"; > + stdout-path = &uart0; > .. Also interestingly, specifying console with stdout-path vs. console=xyz leads to a subtle behaviour change of boot printing. With console=xyz, console_setup() -> __add_preferred_console() sets preferred_console = 0, which doesn't happen with stdout-path. ARC defconfigs have CONFIG_VT_CONSOLE, so tty0 gets registered. For stdout-path case it becomes default (deregistering the earlycon), but not in case of cconsole=xyz. This manifests as a "pause" in boot logging (perceivable if u have linux running in simulation on a slow host or a large initramfs loading etc). printing is restored when the real 8250 console registers towards end of boot. One workaround to this seems to be using @keep_bootcon cmdline option. Asking for all the bells and whistles to be implemented with paramless earlycon is perhaps not fair :-) But this is something developers in this area need to be aware of nevertheless. Thx, -Vineet -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/