From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966004AbcKLBLZ (ORCPT ); Fri, 11 Nov 2016 20:11:25 -0500 Received: from smtp.codeaurora.org ([198.145.29.96]:59332 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965067AbcKLBLX (ORCPT ); Fri, 11 Nov 2016 20:11:23 -0500 DMARC-Filter: OpenDMARC Filter v1.3.1 smtp.codeaurora.org 8C9B96146F Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=pass smtp.mailfrom=okaya@codeaurora.org Subject: Re: [PATCH] PCI: enable extended tags support for PCIe endpoints To: Bjorn Helgaas References: <1474769434-5756-1-git-send-email-okaya@codeaurora.org> <420a9a23-79f8-41d8-c44f-b53f5000c957@codeaurora.org> <20161111205801.GC9868@bhelgaas-glaptop.roam.corp.google.com> Cc: linux-pci@vger.kernel.org, timur@codeaurora.org, cov@codeaurora.org, vikrams@codeaurora.org, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org From: Sinan Kaya Message-ID: <99d136d7-6bce-5faf-c4a9-ba55808c167d@codeaurora.org> Date: Fri, 11 Nov 2016 20:11:19 -0500 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <20161111205801.GC9868@bhelgaas-glaptop.roam.corp.google.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/11/2016 3:58 PM, Bjorn Helgaas wrote: >> I should have checked the capability here before trying to enable it. >> > I'll post a follow up patch on this. >> > >> > Is there any other feedback? > If this were completely safe to enable for every device that supported > it, why would there be an enable bit in Device Control? reading from the ECN here. https://pcisig.com/sites/default/files/specification_documents/ECN_Extended_Tag_Enable_Default_05Sept2008_final.pdf The initial value is implementation specific and functions are allowed to set it to 1 by default. > > I don't know anything about extended tags, but it worries me a little > when there's a "go-fast" switch and no explanation about when and why > we might need to go slo Based on my observation, extended tags increase the number of reads that can be queued up back to back downstream. Otherwise, the requests will not make progress until 1 tag out of 32 gets available. -- Sinan Kaya Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc. Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.