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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B20D3C433F5 for ; Fri, 24 Sep 2021 15:16:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 99FDA61076 for ; Fri, 24 Sep 2021 15:16:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347034AbhIXPRt (ORCPT ); Fri, 24 Sep 2021 11:17:49 -0400 Received: from muru.com ([72.249.23.125]:36942 "EHLO muru.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346962AbhIXPRq (ORCPT ); Fri, 24 Sep 2021 11:17:46 -0400 Received: from localhost (localhost [127.0.0.1]) by muru.com (Postfix) with ESMTPS id C9FB380EE; Fri, 24 Sep 2021 15:16:40 +0000 (UTC) Date: Fri, 24 Sep 2021 18:16:10 +0300 From: Tony Lindgren To: Johan Hovold Cc: Greg Kroah-Hartman , Andy Shevchenko , Jiri Slaby , Vignesh Raghavendra , linux-serial@vger.kernel.org, linux-omap@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 4/6] serial: 8250: Implement prep_tx for power management Message-ID: References: <20210921103346.64824-1-tony@atomide.com> <20210921103346.64824-5-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 * Johan Hovold [210924 14:44]: > On Thu, Sep 23, 2021 at 06:05:36PM +0300, Tony Lindgren wrote: > > * Johan Hovold [210923 12:50]: > > > On Tue, Sep 21, 2021 at 01:33:44PM +0300, Tony Lindgren wrote: > > > > +static int serial8250_prep_tx(struct uart_port *port) > > > > +{ > > > > + struct uart_8250_port *up = up_to_u8250p(port); > > > > + struct device *dev = up->port.dev; > > > > + int err; > > > > + > > > > + if (!(up->capabilities & UART_CAP_RPM)) > > > > + return 0; > > > > + > > > > + if (!pm_runtime_suspended(dev)) { > > > > + pm_runtime_mark_last_busy(dev); > > > > + return 0; > > > > + } > > > > + > > > > + err = pm_request_resume(dev); > > > > + if (err < 0) { > > > > + dev_warn(dev, "prep_tx wakeup failed: %d\n", err); > > > > + return err; > > > > + } > > > > > > How is this supposed to work without a runtime PM usage-counter > > > increment? What's to prevent the port from suspending again while it's > > > transmitting? > > > > Hmm yeah we should at pm_runtime_get() and pm_runtime_put() to write() > > unless serial8250_rpm_get() and serial8250_rpm_put() are doing it. > > If you do the put after just buffering the data it doesn't really solve > anything. Right, sounds like we currently rely on the autosuspend_timeout there. > > Or pair prep with finish and deal with the usage count there. > > Problem is where to call it from. How do you tell the device is done > transmitting? And how should we deal with flow control? Etc. Maybe if the device driver needs to call uart_start() also from runtime PM idle function and if no data allow suspend. Then if there is more data, uart_write() calls uart_start() again, device wakes up and so on. Regards, Tony