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=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 CDE17C433E0 for ; Thu, 4 Mar 2021 12:13:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8A22B64F1E for ; Thu, 4 Mar 2021 12:13:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240154AbhCDMMd (ORCPT ); Thu, 4 Mar 2021 07:12:33 -0500 Received: from mail.kernel.org ([198.145.29.99]:57256 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240310AbhCDMMZ (ORCPT ); Thu, 4 Mar 2021 07:12:25 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 33A82601FC; Thu, 4 Mar 2021 12:11:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1614859905; bh=vQ8RnpXMyqA61QBx4SeK5jkq5GWFtLLQnjzD5WHRFUY=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=WGv7sU7rfZzH64peIaO7rg4Jhprp4fTHooeeqwB7MvvIbDCUFUqLsssKcEzAy2asf IQA0W6YCSRtjZ9fpiQ1rO0ljPzvEbzwmnSagvPT8lqh/jIv5woXp/OUGNo5TG+Gwnl JBZv2FZ2uA6y/nLQRB37PPqy+RyWBL0UoQptqjj+6AP+9qSW/ehe3UUegF0j9PMCKZ deaGQuOfONy+bnMcLK1aesg9XDpmH46WUSNzTv9HvImlelofdJbNKAtu2bRjVzTRre aNAdPybW7uGjkVudBrKzPyiWWndXlGHA0sw/Ymrwh60xOPccCFgWzXX6hc80Vi0ASD 00dLbga6mns8g== Date: Thu, 4 Mar 2021 06:11:43 -0600 From: Bjorn Helgaas To: Minwoo Im Cc: Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= , linux-pci@vger.kernel.org Subject: Re: [PATCH] PCI: Take __pci_set_master in do_pci_disable_device Message-ID: <20210304121143.GA821086@bjorn-Precision-5520> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20210304044013.GA15757@localhost.localdomain> Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Thu, Mar 04, 2021 at 01:40:13PM +0900, Minwoo Im wrote: > On 21-02-24 23:46:00, Krzysztof Wilczyński wrote: > > Hi Minwoo, > > > > Sorry for a very late reply! > > > > [...] > > > > You might need to improve the subject a little - it should be brief but > > > > still informative. > > > > > > > > > __pci_set_mater() has debug log in there so that it would be better to > > > > > take this function. So take __pci_set_master() function rather than > > > > > open coding it. This patch didn't move __pci_set_master() to above to > > > > > avoid churns. > > > > [...] > > > > > > > > It would be __pci_set_master() in the sentence above. Also, perhaps > > > > "use" would be better than "take". Generally, this commit message might > > > > need a little improvement to be more clear why are you do doing this. > > > > > > Sure, if we consolidate bus master enable clear functions to a single > > > one, it would be better to debug and tracing the kernel behaviors. > > > > > > Let me describe this 'why' to the description. > > > > Sounds great! Thank you! > > > > [...] > > > > You could use pci_clear_master(), which we export and that internally > > > > calls __pci_set_master(), so there would be no need to add any forward > > > > declarations or to move anything around in the file. > > > > > > Moving delcaration to above might be churn, and I agree with your point. > > > > I am sure that when it makes sense, then probably folks would not > > object, especially since "churn" can be subjective. > > > > > > Having said that, there is a difference between do_pci_disable_device() > > > > and how __pci_set_master() works - the latter sets the is_busmaster flag > > > > accordingly on the given device whereas the former does not. This might > > > > be of some significance - not sure if we should or should not set this, > > > > since the do_pci_disable_device() does not do that (perhaps it's on > > > > purpose or due to some hisoric reasons). > > > > > > Thanks for pointing out this. I think the difference about > > > `is_busmaster` flag looks like it should not be cleared in case of power > > > suspend case: > > > > > > # Suspend > > > pci_pm_default_suspend() > > > pci_disable_enabled_device() > > > > > > # Resume > > > pci_pm_reenable_device() > > > pci_set_master() <-- This is based on (is_busmaster) > > > > > > > > > Please let me know if I'm missing here, and appreciate pointing that > > > out. Maybe I can post v2 patch with add an argument of whether > > > `is_busmaster` shoud be set inside of the function or not to > > > __pci_set_master()? > > [...] > > > > Nothing is ever simple, isn't it? :-) > > > > We definitely need to make sure that PM can keep relying on the > > is_busmaster flag to restore bus mastering to previous state after the > > device would resume after being suspended. > > Yes, > > > If we add another boolean argument, then we would need to update the > > __pci_set_master() only in two other places, aside of using it in the > > do_pci_disable_device() function, as per (as of 5.11.1 kernel): > > I agree with this approach. I can try it by adding another bool > argument to decide whether to update the is_busmaster flag or not inside > of the __pci_set_master. > > > > > File Line Content > > drivers/pci/pci.c 4308 __pci_set_master(dev, true); > > drivers/pci/pci.c 4319 __pci_set_master(dev, false); > > > > This is not all that terrible, provided that we _really_ do want to > > change this function signature and then add another condition inside. > > > > What do you think? If you still like the idea, then send second version > > over with all the other proposed changes. > > Let me prepare the next version of this patch. Thanks! Can you clarify what the purpose of this patch is? Is it to fix a defect, improve debug output, make the code cleaner, etc? The commit log really just describes *what* the patch does, and I'm looking for the *why*. Bjorn