Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754504AbbBZPyn (ORCPT ); Thu, 26 Feb 2015 10:54:43 -0500 Received: from mail-qc0-f172.google.com ([209.85.216.172]:40905 "EHLO mail-qc0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753976AbbBZPyk (ORCPT ); Thu, 26 Feb 2015 10:54:40 -0500 Message-ID: <54EF41BC.2030900@hurleysoftware.com> Date: Thu, 26 Feb 2015 10:54:36 -0500 From: Peter Hurley User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Rob Herring CC: Greg Kroah-Hartman , Andrew Morton , Arnd Bergmann , Jiri Slaby , "linux-serial@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH -next 00/13] Extensible console matching & direct earlycon References: <1424795830-31223-1-git-send-email-peter@hurleysoftware.com> <54ECD6BA.9070009@hurleysoftware.com> <54EF324C.2080205@hurleysoftware.com> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4280 Lines: 102 On 02/26/2015 09:58 AM, Rob Herring wrote: > On Thu, Feb 26, 2015 at 8:48 AM, Peter Hurley wrote: >> Hi Rob, >> >> On 02/24/2015 03:20 PM, Rob Herring wrote: >>> On Tue, Feb 24, 2015 at 1:53 PM, Peter Hurley wrote: >> >> [...] >> >>>>>> Direct earlycon >>>>>> >>>>>> This feature enables arches and proms to start an earlycon directly, >>>>>> rather than requiring an "earlycon=" command line parameter. >>>>>> Devicetree can already do this via the 'linux,stdout-path' property, >>>>>> but arch and prom code requires direct coupling to the serial driver. >>>>>> >>>>>> This support is implemented by judicious refactoring and the same >>>>>> construct that devicetree and early_param use: a link table containing >>>>>> the necessary information (name and setup() function) to find and >>>>>> bind the appropriate earlycon "driver". >>>>> >>>>> I've skimmed thru this and it looks like a great improvement. >>>>> >>>>> One problem we have currently with DT stdout-path and earlycon is a >>>>> preferred console does not get registered, so the console will get >>>>> switched to tty0 and you lose your console. The problem is DT does not >>>>> know the console name to register a preferred console. It looks like >>>>> this series may help this problem, but I'm not sure and wanted your >>>>> thoughts. >>>> >>>> I thought that of_alias_scan() + of_console_check() caused DT stdout-path >>>> to add_preferred_console() the driver console @ port registration time >>>> via uart_add_one_port() -> of_console_check(). >>>> >>>> Is that not how that works? >>> >>> Yes, I believe that is how it works with earlycon not enabled. This >>> doesn't work when earlycon is enabled with just "earlycon" on the >>> command line. The fix I have is here[1], but I don't like putting DT >>> specifics into the console code. >> >> After much gnashing of teeth and pulling of hair yesterday, I managed >> to mock up the situation you describe, but I need to study it in more >> detail. Some things I did learn: >> >> 1. The serial console _does_ come back up when using stdout-path but the >> line settings don't match, because the serial core sets them to the >> default of 9600n8 if unspecified. > > That may have been what I saw as I tested on QEMU which ignores the > baud rate. But it does stop between the time tty0 is enabled and the > "real" serial console which is a time period we really want the > console. Yeah, that's what my mock-up showed as well: [ 0.000000] Machine model: TI AM335x BeagleBone Black [ 0.000000] earlycon:serial0 options:115200 [ 0.000000] early_omap8250_setup: uart @ 44e09000 [ 0.000000] bootconsole [uart0] enabled .... [ 0.000349] Console: colour dummy device 80x30 [ 0.000367] console [tty0] enabled [ 0.000395] bootconsole [uart0] disabled [ 0.000441] Calibrating delay loop... 995.32 BogoMIPS (lpj=1990656) .... [ 1.097762] Serial: 8250/16550 driver, 32 ports, IRQ sharing disabled [ 1.107659] 44e09000.serial: ttyS0 at MMIO 0x44e09000 (irq = 154, base_baud = 3000000) is a 8250 [ 1.888536] console [ttyS0] enabled [ 1.893036] 481a8000.serial: ttyS4 at MMIO 0x481a8000 (irq = 155, base_baud = 3000000) is a 8250 [ 1.902810] 481aa000.serial: ttyS5 at MMIO 0x481aa000 (irq = 156, base_baud = 3000000) is a 8250 >> 2. The line settings can now be set with stdout-path like, >> stdout-path = "serial0:115200n8" >> but this breaks DT earlycon (as I wrote in the other email you were >> cc'd on). > > Right. We should fix libfdt. > >> 3. omap doesn't support ioremap() at early param parsing :( > > ARM in general does not. I was looking at mach-bcm to see how it was that the iotable_init() didn't blow up, but maybe it does? >> 4. the ARM arch doesn't support fixmap hacking at early param parsing :( > > There's a patch on the list to enable it. It's been slow as fixmap has > been a moving target. Thanks. That's similar to what I cribbed from ARM64 arch last night. Regards, Peter Hurley -- 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/