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=unavailable 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 7E312C433DF for ; Tue, 30 Jun 2020 14:58:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4B34920759 for ; Tue, 30 Jun 2020 14:58:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593529133; bh=PVTznXJyCvr/0gWflz6qqUnQVBqnaxBytLpA2ScZi2o=; h=Date:From:To:Cc:Subject:In-Reply-To:List-ID:From; b=mvLV8enCoLAZDMyvuJ4uz1mvluZ9Lp1TlLLry22WnVnmfrrXF0DLpGRmEujvokPZR 9GGSX5zZEBGCQ8fIWYwlzidzmxM1QkIUXWzpz3zxW+s2chYzWH1V9XhjoCSGA0UHLA pKZSFfmuzNqeT0y853qeqR4G5eum/yv2e1Fq+Z00= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389187AbgF3O6v (ORCPT ); Tue, 30 Jun 2020 10:58:51 -0400 Received: from mail.kernel.org ([198.145.29.99]:42110 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730478AbgF3O6v (ORCPT ); Tue, 30 Jun 2020 10:58:51 -0400 Received: from localhost (mobile-166-175-191-139.mycingular.net [166.175.191.139]) (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 37D8E20675; Tue, 30 Jun 2020 14:58:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593529130; bh=PVTznXJyCvr/0gWflz6qqUnQVBqnaxBytLpA2ScZi2o=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=UGrtzr6l/Dz1zgmF5Gn8ardEy1SuMln8GZ6PHPueInRFfTdL6xyccEtApRZUKzTkL j88PiPHDI8upfuyPX0p7SuHNe/Dn2IeiyQaogjChp6gqk6lkgA3IFhSioq7CnkWU/6 +rJo94TNidFUjFViAcaPH9sNj1lnDmYdpa+4u5b4= Date: Tue, 30 Jun 2020 09:58:48 -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: <20200630145848.GA3419143@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: <20200630140420.7qkuq7wturmaafzf@pali> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 30, 2020 at 04:04:20PM +0200, Pali Rohár wrote: > On Tuesday 30 June 2020 08:51:27 Bjorn Helgaas wrote: > > 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. > > > > What happens when the device is removed after advk_pcie_link_up() > > returns true, but before we actually do the config access? > > Do you mean to remove device physically at runtime? I was told that our > board would crash or issue reset. Removing device from mini PCIe slot > without power off is not supported. Right, I don't think PCIe mini cards support hotplug. > Anyway, currently we are trying to read from device registers even when > no device is connected. So when advk_pcie_link_up() returns true and > after that device is not connected (somehow board and kernel would be > still alive) I guess that it would behave as without applying this > patch. So kernel starts reading from register and would wait until > timeout expires. As device is not connected there would be no answer, > so kernel print error message to dmesg (same as in commit message) and > returns error that read failed. OK, so if I understand correctly, checking advk_pcie_link_up() is strictly an optimization. If we guess wrong (e.g., after calling advk_pcie_link_up(), the link went down because the card was removed, DPC triggered, etc), the only bad thing is that we wait for a timeout; it never causes a crash. If that's the case, I'm fine with this. But please add a comment to that effect. I think several other drivers check for the link being up because we actually crash if we try to read config space when the link is down. That's what I was trying to avoid here. Bjorn