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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=ham 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 7DF73C433E2 for ; Thu, 28 May 2020 16:49:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5882320829 for ; Thu, 28 May 2020 16:49:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590684587; bh=ZvL1zlVb0aD8FKJBrJFoJZtl2vsqUfSH5YS12c2w2SM=; h=Date:From:To:Cc:Subject:In-Reply-To:List-ID:From; b=DgO68R+OZt1DDGq1fW70JPAov6F+AZO2bmYRI8qIfK5S4CsSbGJ0jZ50c+D5aGp7A Ha5gXVwjh0TiGZ4bz7TYjO47+mWSEMVrkQeJs9Xcogvamj7sWN/sNqeFbRhkG0QseS TcgR1I+9o/yTQxbRjaM3iXNbslRKN+FC5wEC3Avs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2405081AbgE1Qtq (ORCPT ); Thu, 28 May 2020 12:49:46 -0400 Received: from mail.kernel.org ([198.145.29.99]:44118 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2405212AbgE1Qtk (ORCPT ); Thu, 28 May 2020 12:49:40 -0400 Received: from localhost (mobile-166-175-190-200.mycingular.net [166.175.190.200]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B6F0D2075A; Thu, 28 May 2020 16:49:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590684580; bh=ZvL1zlVb0aD8FKJBrJFoJZtl2vsqUfSH5YS12c2w2SM=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=sYevLuoNVsyrmYY7rW9ivvtRaYn2l5/dFD1SMhThUEUwgqBgx2xM4JoAwMmw4YZWx Dzr1IMGNmQgl34snFo+oKIZ/ITX3HRABJ3tIplUBnyQwrZh9dOib2KXIhkt229uyWJ 3AXVQZOyeR0LWXJLEqlaQiw+AJ+d/BvhdrXnXQeM= Date: Thu, 28 May 2020 11:49:38 -0500 From: Bjorn Helgaas To: Pali =?iso-8859-1?Q?Roh=E1r?= Cc: Thomas Petazzoni , Lorenzo Pieralisi , Andrew Murray , Bjorn Helgaas , Marek =?iso-8859-1?Q?Beh=FAn?= , Remi Pommarel , Tomasz Maciej Nowak , Xogium , linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] PCI: aardvark: Don't touch PCIe registers if no card connected Message-ID: <20200528164938.GA325239@bjorn-Precision-5520> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200528163809.54f5ldvphrjg3zg3@pali> Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Thu, May 28, 2020 at 06:38:09PM +0200, Pali Rohár wrote: > On Thursday 28 May 2020 11:26:04 Bjorn Helgaas wrote: > > On Thu, May 28, 2020 at 04:31:41PM +0200, Pali Rohár wrote: > > > When there is no PCIe card connected and advk_pcie_rd_conf() or > > > advk_pcie_wr_conf() is called for PCI bus which doesn't belong to emulated > > > root bridge, the aardvark driver throws the following error message: > > > > > > advk-pcie d0070000.pcie: config read/write timed out > > > > > > Obviously accessing PCIe registers of disconnected card is not possible. > > > > > > Extend check in advk_pcie_valid_device() function for validating > > > availability of PCIe bus. If PCIe link is down, then the device is marked > > > as Not Found and the driver does not try to access these registers. > > > > > > Signed-off-by: Pali Rohár > > > --- > > > drivers/pci/controller/pci-aardvark.c | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c > > > index 90ff291c24f0..53a4cfd7d377 100644 > > > --- a/drivers/pci/controller/pci-aardvark.c > > > +++ b/drivers/pci/controller/pci-aardvark.c > > > @@ -644,6 +644,9 @@ static bool advk_pcie_valid_device(struct advk_pcie *pcie, struct pci_bus *bus, > > > if ((bus->number == pcie->root_bus_nr) && PCI_SLOT(devfn) != 0) > > > return false; > > > > > > + if (bus->number != pcie->root_bus_nr && !advk_pcie_link_up(pcie)) > > > + return false; > > > > I don't think this is the right fix. This makes it racy because the > > link may go down after we call advk_pcie_valid_device() but before we > > perform the config read. > > Yes, it is racy, but I do not think it cause problems. Trying to read > PCIe registers when device is not connected cause just those timeouts, > printing error message and increased delay in advk_pcie_wait_pio() due > to polling loop. This patch reduce unnecessary access to PCIe registers > when advk_pcie_wait_pio() polling just fail. > > I think it is a good idea to not call blocking advk_pcie_wait_pio() when > it is not needed. We could have faster enumeration of PCIe buses when > card is not connected. Maybe advk_pcie_check_pio_status() and advk_pcie_wait_pio() could be combined so we could get the correct error status as soon as it's available, without waiting for a timeout? In any event, the "return PCIBIOS_SET_FAILED" needs to be fixed. Most callers of config read do not check for failure, but most of the ones that do, check for "val == ~0". Only a few check for a status of other than PCIBIOS_SUCCESSFUL. > > I have no objection to removing the "config read/write timed out" > > message. The "return PCIBIOS_SET_FAILED" in the read case probably > > should be augmented by setting "*val = 0xffffffff". > > > > > return true; > > > } > > > > > > -- > > > 2.20.1 > > >