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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A7827C4332F for ; Fri, 3 Nov 2023 18:20:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232839AbjKCSU7 (ORCPT ); Fri, 3 Nov 2023 14:20:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39280 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230197AbjKCSU6 (ORCPT ); Fri, 3 Nov 2023 14:20:58 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E5CC1D4D; Fri, 3 Nov 2023 11:20:55 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4D9CCC433C8; Fri, 3 Nov 2023 18:20:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1699035655; bh=7tsGjmrJ/IXbOi51N3JxFSTY9p457HkH2KZbbUbO1iE=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=IqXu1JfP1CdmSvVNo4GhiVPq19YApTjCfV10gbi+4ezSJBuhOQLrV7Lld2xJM2LUx puek0io2gVD/ianpjw+DsgRCFgXKFqvgMh2EJ219wgEkW/tE8N7OiaSdFhk2kqu2w5 kKxQmgUkpWFKi6oiKTUG09k7i4ZA6/r78auAsFNwwVP31aP4ENBsfSzoCSxTMO/WYg MeOqfdN0yFZ9GgzpMZ5z7Tq1oPXGtTP7pVkkWorYHbWofeKhVFz7VsGNk5fSnIpYcR e5ZuduAjfrGeozEFDZXcOJ5gXMOZ9YZ/c/aH1dXMq79ehpg4meXTG0jK8gBKcqjl8t uLu7wzcWes8gA== Date: Fri, 3 Nov 2023 13:20:53 -0500 From: Bjorn Helgaas To: Vidya Sagar Cc: Lorenzo Pieralisi , Vikram Sethi , Thierry Reding , Jonathan Hunter , Krishna Thota , "linux-pci@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: Question: Clearing error bits in the root port post enumeration Message-ID: <20231103182053.GA160440@bhelgaas> 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-pci@vger.kernel.org On Tue, Oct 31, 2023 at 12:26:31PM +0000, Vidya Sagar wrote: > Hi folks, > > I would like to know your comments on the following scenario where > we are observing the root port logging errors because of the > enumeration flow being followed. > > DUT information: > - Has a root port and an endpoint connected to it > - Uses ECAM mechanism to access the configuration space > - Booted through ACPI flow > - Has a Firmware-First approach for handling the errors > - System is configured to treat Unsupported Requests as > AdvisoryNon-Fatal errors > > As we all know, when a configuration read request comes in for a > device number that is not implemented, a UR would be returned as per > the PCIe spec. > > As part of the enumeration flow on DUT, when the kernel reads offset > 0x0 of B:D:F=0:0:0, the root port responds with its valid Vendor-ID > and Device-ID values. But, when B:D:F=0:1:0 is probed, since there > is no device present there, the root port responds with an > Unsupported Request and simultaneously logs the same in the Device > Status register (i.e. bit-3). Because of it, there is a UR logged > in the Device Status register of the RP by the time enumeration is > complete. > > In the case of AER capability natively owned by the kernel, the AER > driver's init call would clear all such pending bits. > > Since we are going with the Firmware-First approach, and the system > is configured to treat Unsupported Requests as AdvisoryNon-Fatal > errors, only a correctable error interrupt can be raised to the > Firmware which takes care of clearing the corresponding status > registers. The firmware can't know about the UnsupReq bit being set > as the interrupt it received is for a correctable error hence it > clears only bits related to correctable error. > > All these events leave a freshly booted system with the following > bits set. > > Secondary status: 66MHz- FastB2B- ParErr- DEVSEL=fast >TAbort- DevSta: CorrErr- NonFatalErr- FatalErr- UnsupReq+ AuxPwr- TransPend- (UnsupReq) > UESta: DLP- SDES- TLP- FCP- CmpltTO- CmpltAbrt- UnxCmplt- RxOF- MalfTLP- ECRC- UnsupReq+ ACSViol- (UnsupReq) > > Since the reason for UR is well understood at this point, I would > like to weigh in on the idea of clearing the aforementioned bits in > the root port once the enumeration is done particularly to cater to > the configurations where Firmware-First approach is in place. > Please let me know your comments on this approach. I think Secondary status (PCI_SEC_STATUS) is always owned by the OS and is not affected by _OSC negotiation, right? Linux does basically nothing with that today, but I think it *could* clear the "Received Master Abort" bit. I'm not very familiar with Advisory Non-Fatal errors. I'm curious about the UESta situation: why can't firmware know about UnsupReq being set? I assume PCI_ERR_COR_ADV_NFAT is the Correctable Error Status bit the firmware *does* see and clear. But isn't the whole point of Advisory Non-Fatal errors that an error that is logged as an Uncorrectable Error and that normally would be signaled with ERR_NONFATAL is signaled with ERR_COR instead? So doesn't PCI_ERR_COR_ADV_NFAT being set imply that some PCI_ERR_UNCOR_STATUS must be set as well? If so, I would think firmware *could* figure that out and clear the PCI_ERR_UNCOR_STATUS bit. Bjorn