Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933093AbdCaMYX (ORCPT ); Fri, 31 Mar 2017 08:24:23 -0400 Received: from mga14.intel.com ([192.55.52.115]:43564 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932932AbdCaMYW (ORCPT ); Fri, 31 Mar 2017 08:24:22 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.36,251,1486454400"; d="scan'208";a="81357131" Date: Fri, 31 Mar 2017 20:19:44 +0800 From: Wu Hao To: Greg KH Cc: atull@kernel.org, moritz.fischer@ettus.com, linux-fpga@vger.kernel.org, linux-kernel@vger.kernel.org, luwei.kang@intel.com, yi.z.zhang@intel.com, Tim Whisonant , Enno Luebbers , Shiva Rao , Christopher Rauer , Xiao Guangrong Subject: Re: [PATCH 02/16] fpga: add FPGA device framework Message-ID: <20170331121944.GA1312@hao-dev> References: <1490875696-15145-1-git-send-email-hao.wu@intel.com> <1490875696-15145-3-git-send-email-hao.wu@intel.com> <20170331060909.GA7621@kroah.com> <20170331074842.GA17067@hao-dev> <20170331090328.GA6220@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170331090328.GA6220@kroah.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4111 Lines: 95 On Fri, Mar 31, 2017 at 11:03:28AM +0200, Greg KH wrote: > On Fri, Mar 31, 2017 at 03:48:42PM +0800, Wu Hao wrote: > > On Fri, Mar 31, 2017 at 08:09:09AM +0200, Greg KH wrote: > > > On Thu, Mar 30, 2017 at 08:08:02PM +0800, Wu Hao wrote: > > > > During FPGA device (e.g PCI-based) discovery, platform devices are > > > > registered for different FPGA function units. But the device node path > > > > isn't quite friendly to applications. > > > > > > > > Consider this case, applications want to access child device's sysfs file > > > > for some information. > > > > > > > > 1) Access using bus-based path (e.g PCI) > > > > > > > > /sys/bus/pci/devices/xxxxx/fpga_func_a.0/sysfs_file > > > > > > > > From the path, it's clear which PCI device is the parent, but not perfect > > > > solution for applications. PCI device BDF is not fixed, application may > > > > need to search all PCI device to find the actual FPGA Device. > > > > > > > > 2) Or access using platform device path > > > > > > > > /sys/bus/platform/devices/fpga_func_a.0/sysfs_file > > > > > > > > Applications find the actual function by name easily, but no information > > > > about which fpga device it belongs to. It's quite confusing if multiple > > > > FPGA devices are in one system. > > > > > > > > 'FPGA Device' class is introduced to resolve this problem. Each node under > > > > this class represents a fpga device, which may have one or more child > > > > devices. Applications only need to search under this FPGA Device class > > > > folder to find the child device node it needs. > > > > > > > > For example, for the platform has 2 fpga devices, each fpga device has > > > > 3 child devices, the hierarchy looks like this. > > > > > > > > Two nodes are under /sys/class/fpga/: > > > > /sys/class/fpga/fpga.0 > > > > /sys/class/fpga/fpga.1 > > > > > > > > Each node has 1 function A device and 2 function B devices: > > > > /sys/class/fpga/fpga.0/func_a.0 > > > > /sys/class/fpga/fpga.0/func_b.0 > > > > /sys/class/fpga/fpga.0/func_b.1 > > > > > > > > /sys/class/fpga/fpga.1/func_a.1 > > > > /sys/class/fpga/fpga.1/func_b.2 > > > > /sys/class/fpga/fpga.1/func_b.3 > > > > > > > > This following APIs are provided by FPGA device framework: > > > > * fpga_dev_create > > > > Create fpga device under the given parent device. > > > > * fpga_dev_destroy > > > > Destroy fpga device > > > > > > > > The following sysfs files are created: > > > > * /sys/class/fpga//name > > > > Name of the fpga device. > > > > > > How does this interact with the existing "fpga class" that is in the > > > kernel already? > > > > The fpga-dev introduced by this patch, is only a container device, and > > drivers could register different functions under it. Per my understanding, > > the existing "fpga class", including fpga-region, fpga-bridge and > > fpga-manager, is used to provide reconfiguration function for FPGA. So > > driver can create child node using this existing "fpga class" to provide > > FPGA reconfiguration function, and more nodes under this container for > > different functions for given FPGA device. > > > > For Intel FPGA device, partial reconfiguration is only one function of > > Intel FPGA Management Engine (FME). FME driver creates fpga_manager under > > below path for partial reconfiguration, and other interfaces for more > > functions, e.g power management, virtualization support and etc. > > > > /sys/class/fpga///fpga_manager > > So there is now two different levels of fpga class interfaces? > > I'm not disagreeing with this, just that it seems a bit confusing, don't > you think? I am not so sure, but the main purpose of fpga-dev, is trying to provide enduser a more clear sysfs hierarchy reflecting the real hardware. And fpga-things can be registered to fpga-dev directly if the hardware arch is simple. >From enduser point of view, he could find everything of this FPGA device under /sys/class/fpga//, including all fpga-regions, fpga-bridges and fpga-managers. I feel it is not a bad choice. :) Thanks Hao > > greg k-h