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 X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2629CC4332F for ; Thu, 23 Sep 2021 15:02:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0F36D61107 for ; Thu, 23 Sep 2021 15:02:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241854AbhIWPEC (ORCPT ); Thu, 23 Sep 2021 11:04:02 -0400 Received: from muru.com ([72.249.23.125]:36512 "EHLO muru.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241798AbhIWPEB (ORCPT ); Thu, 23 Sep 2021 11:04:01 -0400 Received: from localhost (localhost [127.0.0.1]) by muru.com (Postfix) with ESMTPS id 1CA4580C0; Thu, 23 Sep 2021 15:02:57 +0000 (UTC) Date: Thu, 23 Sep 2021 18:02:27 +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 3/6] serial: core: Add new prep_tx for power management Message-ID: References: <20210921103346.64824-1-tony@atomide.com> <20210921103346.64824-4-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 [210923 12:46]: > On Tue, Sep 21, 2021 at 01:33:43PM +0300, Tony Lindgren wrote: > > If the serial driver implements PM runtime with autosuspend, the port may > > be powered off for TX. To wake up the port, let's add new prep_tx() call > > for serial drivers to implement as needed. We call it from serial > > write_room() and write() functions. If the serial port is not enabled, > > we just return 0. > > This isn't right. If there's room in the driver buffer, there's no > reason to not accept those characters. Maybe. We might get away with returning zero bytes written in write(). But to me it seems better to stop things early when write is known to not succeed. > It's the drivers responsibility to resume writing when write() is > called and that me need to be done in a runtime resume callback in case > the device is suspended. I think we currently need to return zero bytes written from write() when the serial port is not usable. I don't think we can return a fake number of bytes written from write(). And even if we could return a fake number of bytes written, we could run into issues doing the real write to the serial port. > No need to be patching line disciplines for this. Do you see issues with handling the errors in line disciplines? Regards, Tony