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=-21.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 4A3D8C432BE for ; Wed, 4 Aug 2021 23:17:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2D0D76109F for ; Wed, 4 Aug 2021 23:17:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235582AbhHDXRq (ORCPT ); Wed, 4 Aug 2021 19:17:46 -0400 Received: from mail.kernel.org ([198.145.29.99]:41786 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229987AbhHDXRo (ORCPT ); Wed, 4 Aug 2021 19:17:44 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id AA52B61029; Wed, 4 Aug 2021 23:17:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1628119051; bh=LB/yWwNyZPNern/LMAfi3Q2yQX76M51Zx+XEZVhnae8=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=EKJq8oPfu3fKGmj6h/YUHkspfkI8cW8KKMtkE8AMSrBiM7SrQ3IlqFY8gBprdsKEw e9K4jQjRXDSQ2EeWLceqX6ogolzZldyVn7afLljP4rSxY61IMB9aL4gr2waOSSok9i IzGPOGEjpOWxzOhbCa43SnikCpXaDUIsaxIDcjJdmlVhs+pul3fc7JZmt1untR120O l1Kv4C/t40Q3MPkA3g/ljwWl8eHZ3frdiAPkRjQq6wVM5nwTEdqkdrbyJ543VB8fVT fa6GhvOdtp09nHMCBFtfDWsMWQVR71cWbXZZKsE+4xi7Z90aT0ubcohtpvGREn4kO4 AwQO/ZVz0xstA== Date: Wed, 4 Aug 2021 18:17:29 -0500 From: Bjorn Helgaas To: Dongdong Liu Cc: hch@infradead.org, kw@linux.com, logang@deltatee.com, leon@kernel.org, linux-pci@vger.kernel.org, rajur@chelsio.com, hverkuil-cisco@xs4all.nl, linux-media@vger.kernel.org, netdev@vger.kernel.org Subject: Re: [PATCH V7 4/9] PCI: Enable 10-Bit Tag support for PCIe Endpoint devices Message-ID: <20210804231729.GA1679826@bjorn-Precision-5520> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1628084828-119542-5-git-send-email-liudongdong3@huawei.com> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, Aug 04, 2021 at 09:47:03PM +0800, Dongdong Liu wrote: > 10-Bit Tag capability, introduced in PCIe-4.0 increases the total Tag > field size from 8 bits to 10 bits. > > PCIe spec 5.0 r1.0 section 2.2.6.2 "Considerations for Implementing > 10-Bit Tag Capabilities" Implementation Note. > For platforms where the RC supports 10-Bit Tag Completer capability, > it is highly recommended for platform firmware or operating software > that configures PCIe hierarchies to Set the 10-Bit Tag Requester Enable > bit automatically in Endpoints with 10-Bit Tag Requester capability. This > enables the important class of 10-Bit Tag capable adapters that send > Memory Read Requests only to host memory. Quoted material should be set off with a blank line before it and indented by two spaces so it's clear exactly what comes from the spec and what you've added. For example, see https://git.kernel.org/linus/ec411e02b7a2 We need to say why we assume it's safe to enable 10-bit tags for all devices below a Root Port that supports them. I think this has to do with switches being required to forward 10-bit tags correctly even if they were designed before 10-bit tags were added to the spec. And it should call out any cases where it is *not* safe, e.g., if P2P traffic is an issue. If there are cases where we don't want to enable 10-bit tags, whether it's to enable P2P traffic or merely to work around device defects, that ability needs to be here from the beginning. If somebody needs to bisect with 10-bit tags disabled, we don't want a bisection hole between this commit and the commit that adds the control. > Signed-off-by: Dongdong Liu > Reviewed-by: Christoph Hellwig > --- > drivers/pci/probe.c | 47 ++++++++++++++++++++++++++++++++++++++++++++++- > include/linux/pci.h | 2 ++ > 2 files changed, 48 insertions(+), 1 deletion(-) > > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c > index c83245b..3da7baa 100644 > --- a/drivers/pci/probe.c > +++ b/drivers/pci/probe.c > @@ -2029,10 +2029,42 @@ static void pci_configure_mps(struct pci_dev *dev) > p_mps, mps, mpss); > } > > +static void pci_configure_10bit_tags(struct pci_dev *dev) > +{ > + struct pci_dev *bridge; > + > + if (!(dev->pcie_devcap2 & PCI_EXP_DEVCAP2_10BIT_TAG_COMP)) > + return; > + > + if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT) { > + dev->ext_10bit_tag = 1; > + return; > + } > + > + bridge = pci_upstream_bridge(dev); > + if (bridge && bridge->ext_10bit_tag) > + dev->ext_10bit_tag = 1; Is it meaningful to set dev->ext_10bit_tag when "dev" is a VF? I suspect only if the VF could be a switch. Is that possible? If not, I think the dev->is_virtfn check could be done first. > + > + /* > + * 10-Bit Tag Requester Enable in Device Control 2 Register is RsvdP > + * for VF. (Per 9.3.5.10) > + */ > + if (dev->is_virtfn) > + return; > + > + if (pci_pcie_type(dev) == PCI_EXP_TYPE_ENDPOINT && > + dev->ext_10bit_tag == 1 && > + (dev->pcie_devcap2 & PCI_EXP_DEVCAP2_10BIT_TAG_REQ)) { > + pci_dbg(dev, "enabling 10-Bit Tag Requester\n"); > + pcie_capability_set_word(dev, PCI_EXP_DEVCTL2, > + PCI_EXP_DEVCTL2_10BIT_TAG_REQ_EN); > + } > +} > + > int pci_configure_extended_tags(struct pci_dev *dev, void *ign) > { > struct pci_host_bridge *host; > - u16 ctl; > + u16 ctl, ctl2; > int ret; > > if (!pci_is_pcie(dev)) > @@ -2045,6 +2077,10 @@ int pci_configure_extended_tags(struct pci_dev *dev, void *ign) > if (ret) > return 0; > > + ret = pcie_capability_read_word(dev, PCI_EXP_DEVCTL2, &ctl2); > + if (ret) > + return 0; > + > host = pci_find_host_bridge(dev->bus); > if (!host) > return 0; > @@ -2059,6 +2095,12 @@ int pci_configure_extended_tags(struct pci_dev *dev, void *ign) > pcie_capability_clear_word(dev, PCI_EXP_DEVCTL, > PCI_EXP_DEVCTL_EXT_TAG); > } > + > + if (ctl2 & PCI_EXP_DEVCTL2_10BIT_TAG_REQ_EN) { > + pci_info(dev, "disabling 10-Bit Tags\n"); > + pcie_capability_clear_word(dev, PCI_EXP_DEVCTL2, > + PCI_EXP_DEVCTL2_10BIT_TAG_REQ_EN); > + } > return 0; > } > > @@ -2067,6 +2109,9 @@ int pci_configure_extended_tags(struct pci_dev *dev, void *ign) > pcie_capability_set_word(dev, PCI_EXP_DEVCTL, > PCI_EXP_DEVCTL_EXT_TAG); > } > + > + pci_configure_10bit_tags(dev); > + > return 0; > } > > diff --git a/include/linux/pci.h b/include/linux/pci.h > index 9aab67f..af6cb53 100644 > --- a/include/linux/pci.h > +++ b/include/linux/pci.h > @@ -393,6 +393,8 @@ struct pci_dev { > #endif > unsigned int eetlp_prefix_path:1; /* End-to-End TLP Prefix */ > > + unsigned int ext_10bit_tag:1; /* 10-Bit Tag Completer Supported > + from root to here */ > pci_channel_state_t error_state; /* Current connectivity state */ > struct device dev; /* Generic device interface */ > > -- > 2.7.4 >