From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756480AbcCXDRM (ORCPT ); Wed, 23 Mar 2016 23:17:12 -0400 Received: from mail-pf0-f173.google.com ([209.85.192.173]:35978 "EHLO mail-pf0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753740AbcCXDRK (ORCPT ); Wed, 23 Mar 2016 23:17:10 -0400 Subject: Re: Nonterministic hang during bootconsole/console handover on ath79 To: Matthias Schiffer References: <56F07DA1.8080404@universe-factory.net> <56F0B189.2080206@hurleysoftware.com> <56F143A8.6020601@universe-factory.net> <56F16708.4020109@hurleysoftware.com> <56F2D523.6000405@universe-factory.net> <56F3386A.5040100@hurleysoftware.com> <56F34C61.50505@universe-factory.net> Cc: Ralf Baechle , gregkh@linuxfoundation.org, jslaby@suse.com, linux-mips@linux-mips.org, linux-serial@vger.kernel.org, "linux-kernel@vger.kernel.org" From: Peter Hurley Message-ID: <56F35C33.7030608@hurleysoftware.com> Date: Wed, 23 Mar 2016 20:17:07 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: <56F34C61.50505@universe-factory.net> 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 On 03/23/2016 07:09 PM, Matthias Schiffer wrote: >>> autoconfig_16550a() is doing all kinds of weird checks to detect different >>> hardware by writing a lot of register values which are documented as >>> reserved in the AR7242 datasheet (there's a leaked version going around >>> that can be easily googled...), no idea if any of those are problematic. >>> Just setting UPF_FIXED_TYPE as suggested by Peter would avoid that code >>> altogether. >> >> That's just a debugging patch and not appropriate for permanent use, >> the reason being that this uart is _not_ 16550 compatible (or even 16450 >> compatible). >> >> The three options for 8250 driver support for this part are: >> 1. Similar to the debugging patch, set UPF_FIXED_TYPE but set port type >> to PORT_8250 instead. This will lose FIFO support so 115K won't be >> possible and likely neither will 38400. >> >> 2. Set UPF_FIXED_TYPE but define a new PORT_* value and add support for >> this PORT_* value to uart_config array, uapi headers, and anywhere >> the scratch register is used. >> >> 3. As with 2. above but don't set UPF_FIXED_TYPE and add a probe function >> that detects ports of this type to autoconfig(). I don't recommend this >> method. >> >> This requirement is independent of fixing prom_putchar_ar71xx(). >> > > I can send patches for all of this, and I think that 2. would be the nicest > solution. I've noticed though that include/uapi/linux/serial_core.h is > experiencing a little "overflow": PORT_MAX_8250 has grown just below the > first non-8250 entry. Ugh. Thanks for noting this. > Should I just add the new entry at the bottom (and > thus grow the uart_config array by ~85 unused entries)? What about > PORT_MAX_8250 (used at least in drivers/tty/serial/8250/8250_of.c)? None of the above, unfortunately. Ok, plan B. I need to clean off a dusty series that adds probe steering and bugs pass-thru for 8250 sub-drivers and platform data. Then add a UART_BUG_NOSCR to indicate a uart does not have a scratch register (like this one). Then for this uart, set UPF_FIXED_TYPE and type to PORT_16550A, with UART_BUG_NOSCR flag. Couple of days because I'm in the middle of something else, ok? Regards, Peter Hurley