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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 4C77DCA9EAE for ; Tue, 29 Oct 2019 09:31:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 27B59208E3 for ; Tue, 29 Oct 2019 09:31:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732793AbfJ2Jb3 (ORCPT ); Tue, 29 Oct 2019 05:31:29 -0400 Received: from mga01.intel.com ([192.55.52.88]:24077 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726025AbfJ2Jb3 (ORCPT ); Tue, 29 Oct 2019 05:31:29 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga101.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 29 Oct 2019 02:31:28 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.68,243,1569308400"; d="scan'208";a="202787906" Received: from linux.intel.com ([10.54.29.200]) by orsmga003.jf.intel.com with ESMTP; 29 Oct 2019 02:31:27 -0700 Received: from [10.226.39.46] (ekotax-MOBL.gar.corp.intel.com [10.226.39.46]) by linux.intel.com (Postfix) with ESMTP id A1C6A5802C4; Tue, 29 Oct 2019 02:31:19 -0700 (PDT) Subject: Re: [PATCH v4 3/3] pci: intel: Add sysfs attributes to configure pcie link To: Bjorn Helgaas Cc: Andrew Murray , jingoohan1@gmail.com, gustavo.pimentel@synopsys.com, lorenzo.pieralisi@arm.com, robh@kernel.org, martin.blumenstingl@googlemail.com, linux-pci@vger.kernel.org, hch@infradead.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, andriy.shevchenko@intel.com, cheol.yong.kim@intel.com, chuanhua.lei@linux.intel.com, qi-ming.wu@intel.com, "Rafael J. Wysocki" , linux-pm@vger.kernel.org References: <20191022125950.GA133170@google.com> From: Dilip Kota Message-ID: Date: Tue, 29 Oct 2019 17:31:18 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20191022125950.GA133170@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On 10/22/2019 8:59 PM, Bjorn Helgaas wrote: > [+cc Rafael, linux-pm, beginning of discussion at > https://lore.kernel.org/r/d8574605f8e70f41ce1e88ccfb56b63c8f85e4df.1571638827.git.eswara.kota@linux.intel.com] > > On Tue, Oct 22, 2019 at 05:27:38PM +0800, Dilip Kota wrote: >> On 10/22/2019 1:18 AM, Bjorn Helgaas wrote: >>> On Mon, Oct 21, 2019 at 02:38:50PM +0100, Andrew Murray wrote: >>>> On Mon, Oct 21, 2019 at 02:39:20PM +0800, Dilip Kota wrote: >>>>> PCIe RC driver on Intel Gateway SoCs have a requirement >>>>> of changing link width and speed on the fly. >>> Please add more details about why this is needed. Since you're adding >>> sysfs files, it sounds like it's not actually the *driver* that needs >>> this; it's something in userspace? >> We have use cases to change the link speed and width on the fly. >> One is EMI check and other is power saving. Some battery backed >> applications have to switch PCIe link from higher GEN to GEN1 and >> width to x1. During the cases like external power supply got >> disconnected or broken. Once external power supply is connected then >> switch PCIe link to higher GEN and width. > That sounds plausible, but of course nothing there is specific to the > Intel Gateway, so we should implement this generically so it would > work on all hardware. Agree. > > I'm not sure what the interface should look like -- should it be a > low-level interface as you propose where userspace would have to > identify each link of interest, or is there some system-wide > power/performance knob that could tune all links? Cc'd Rafael and > linux-pm in case they have ideas. To my knowledge sysfs is the appropriate way to go. If there are any other best possible knobs, will be helpful. Regards, Dilip > > Bjorn