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 56BAAC433EF for ; Mon, 11 Apr 2022 10:26:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345436AbiDKK2m (ORCPT ); Mon, 11 Apr 2022 06:28:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37662 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345834AbiDKK2B (ORCPT ); Mon, 11 Apr 2022 06:28:01 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E8BD02253D; Mon, 11 Apr 2022 03:25:47 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 81B5961494; Mon, 11 Apr 2022 10:25:47 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D43D2C385A5; Mon, 11 Apr 2022 10:25:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1649672746; bh=ToeC9tEdnIhlAOR1pPNmn1re702gqOBJ1GoLQPVv7K0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=SrhLIUOEc1lbZh4BFijvTmYSn+pFIKhlkruchPzE/FS52FFP880HJHvxTZE0an0+2 9fiGIoeBCdM6izDDe1VOtswW5OnW8QQLFNLlFdQH1XJ3o4I55FNV9Ag1755pLSEHjc g1e7JN/LnHyAERGrPlC74jn88/tFhhyK0IGcjCB2hWAVdhZq33ASMucq4q3SC8y5aE y5/7GHpoTJdGnlS679MWQYbwQchrJXutdAEGwqq1JZ52AHLGrEa4d8+YayNSTWEK/Y IMwCSoIXYHrYLX+F66ElFEgwN6RZpsGI9Sa1Vu2SFWp00uySGSmkfIAvvPVUf+39BH y3Dz6az2EPoZA== Received: from johan by xi.lan with local (Exim 4.94.2) (envelope-from ) id 1ndrEq-0003zS-9G; Mon, 11 Apr 2022 12:25:40 +0200 Date: Mon, 11 Apr 2022 12:25:40 +0200 From: Johan Hovold To: Tony Lindgren Cc: Greg Kroah-Hartman , Andy Shevchenko , Jiri Slaby , Sebastian Andrzej Siewior , Vignesh Raghavendra , linux-serial@vger.kernel.org, linux-omap@vger.kernel.org, linux-kernel@vger.kernel.org, "Matwey V . Kornilov" , Steffen Trumtrar , Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= Subject: Re: [PATCH 1/2] serial: 8250: Fix runtime PM for start_tx() for RS485 Message-ID: References: <20220411094805.45696-1-tony@atomide.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 11, 2022 at 01:10:34PM +0300, Tony Lindgren wrote: > * Johan Hovold [220411 09:54]: > > On Mon, Apr 11, 2022 at 12:48:04PM +0300, Tony Lindgren wrote: > > > diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c > > > --- a/drivers/tty/serial/8250/8250_port.c > > > +++ b/drivers/tty/serial/8250/8250_port.c > > > @@ -1681,8 +1681,10 @@ static void serial8250_start_tx(struct uart_port *port) > > > return; > > > > > > if (em485 && > > > - em485->active_timer == &em485->start_tx_timer) > > > + em485->active_timer == &em485->start_tx_timer) { > > > + serial8250_rpm_put_tx(up); > > > return; > > > + } > > > > I was just taking a quick look at your report about this and also > > noticed this return statement. > > > > The runtime PM implementation is a bit of mess as we've discussed > > elsewhere, but the change you propose here doesn't look right. > > Frankly "a bit of mess" applies "a bit more" than just the serial runtime > PM :) Heh. I'm afraid that's all too true. :) > > start_tx() can be deferred in the rs485 case, but that doesn't mean you > > should suspend the device here. In fact, that look like it would just > > break runtime PM (the parts that may work to some extent). > > AFAIK there's currently nothing paired with the serial8250_rpm_get_tx(up) > call at the beginning of serial8250_start_tx() for the early exit cases > if start_tx_rs485() or __start_tx() won't get called. > > Care to clarify a bit more what you have in mind? The problem is that that serial8250_rpm_put_tx() you're adding may suspend the device unconditionally (i.e. regardless of any previous calls to serial8250_rpm_get_tx()). If rs485 tx is just being deferred you mustn't suspend the device before it has had a chance to start transmitting. Johan