From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 09B26C4332F for ; Fri, 11 Nov 2022 17:16:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234136AbiKKRQK (ORCPT ); Fri, 11 Nov 2022 12:16:10 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55416 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234306AbiKKRQJ (ORCPT ); Fri, 11 Nov 2022 12:16:09 -0500 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1DF4620F71; Fri, 11 Nov 2022 09:16:04 -0800 (PST) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id B3E6A22427; Fri, 11 Nov 2022 17:16:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1668186962; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=FxrxM7pL3XKtifIuT+LlAb2dWxKEfCKW4HflKcsOazM=; b=Bx93kEFIydrek2IJhS1lyxdnzNwsqiFWcSHlAxlTXbGbLl8Lk667JwSy1+8nQrjVP4gzUK pk7Pxa39UFsq+onAdTpLvmGhPWQO4bmOhnEYXxKi2ONuoPJKIvtHs/cqCGFk2+29VflLLL YjzXL5z0HLnd9i/Kgm5/5Wa6hVfQATQ= Received: from suse.cz (unknown [10.100.201.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 4937A2C145; Fri, 11 Nov 2022 17:16:02 +0000 (UTC) Date: Fri, 11 Nov 2022 18:15:58 +0100 From: Petr Mladek To: John Ogness Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Greg Kroah-Hartman , Jiri Slaby , linux-serial@vger.kernel.org, Bartosz Golaszewski , Geert Uytterhoeven Subject: Re: [PATCH printk v3 40/40] tty: serial: sh-sci: use setup() callback for early console Message-ID: References: <20221107141638.3790965-1-john.ogness@linutronix.de> <20221107141638.3790965-41-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221107141638.3790965-41-john.ogness@linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org Ccing Bartosz who should be familiar with the early platform code. On Mon 2022-11-07 15:22:38, John Ogness wrote: > When setting up the early console, the setup() callback of the > regular console is used. It is called manually before registering > the early console instead of providing a setup() callback for the > early console. This is probably because the early setup needs a > different @options during the early stage. This last sentece makes a bit nervous ;-) I think that I understood it in the end, see below. > The issue here is that the setup() callback is called without the > console_list_lock held and functions such as uart_set_options() > expect that. > > Rather than manually calling the setup() function before registering, > provide an early console setup() callback that will use the different > early options. This ensures that the error checking, ordering, and > locking context when setting up the early console are correct. > > Note that technically the current implementation works because it is > only used in early boot. And since the early console setup is > performed before registering, it cannot race with anything and thus > does not need any locking. However, longterm maintenance is easier > when drivers rely on the subsystem API rather than manually > implementing steps that could cause breakage in the future. > > Signed-off-by: John Ogness > --- > drivers/tty/serial/sh-sci.c | 17 +++++++++++++---- > 1 file changed, 13 insertions(+), 4 deletions(-) > > diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c > index 62f773286d44..f3a1cfec757a 100644 > --- a/drivers/tty/serial/sh-sci.c > +++ b/drivers/tty/serial/sh-sci.c > @@ -3054,15 +3054,26 @@ static struct console serial_console = { > }; > > #ifdef CONFIG_SUPERH > +static char early_serial_buf[32]; > + > +static int early_serial_console_setup(struct console *co, char *options) > +{ > + WARN_ON(options); > + /* > + * Use @early_serial_buf because @options will always be > + * NULL at this early stage. > + */ The commit message says that we use @early_serial_buf because the early console probably needs another parameters. It suggests that @options might be for the later stage and we need to replace them there. Are we sure that this will always be NULL? Background: The console->setup() is called in two situations: 1. when the console is registered as the default console, see try_enable_default_console(). In this case, @options is really NULL. 2. when the console is preferred either via the commnadline, or device tree, or SPCR, see try_enable_preferred_console(). In this case, some real @options would be passed. From the code POV, the preferred consoles are added by calling add_preferred_console(). Now, it means that the WARN_ON() is correct only when this console is always registered before the preferred consoles are defined. I think that this is really the case. This console is actually registered via the "earlyprintk" parameter that is proceed by the arch-specific code before the preferred consoles are added the standard way via the kernel commandline. Note that "earlyprintk" and "earlycon" are two different parameters. "earlyprintk" normally initializes "early_console" that is called directly by early_printk(). It is used for super early debugging. These messages even do not end in the ring buffer. "earlycon" defines a "normal" console that is used by the standard printk(). They are later replaced by properly initialized console drivers that are in sysfs, ... Note that "earlycon" calls add_preferred_console() so that the @options are stored and passed from try_enable_preferred_console(). But "earlyprintk" does not call add_preferred_console() so we need this hack to store and pass the console options another way. > + return serial_console_setup(co, early_serial_buf); > +} > + So I would do something like: static int early_serial_console_setup(struct console *co, char *options) { /* * This early console is registered using earlyprintk= parameter * that does not call add_preferred_console(). The @options * are passed using a custom buffer. */ WARN_ON(options); return serial_console_setup(co, early_serial_buf); } Also we should explain this in the commit message. Best Regards, Petr