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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 B2807C0650E for ; Thu, 4 Jul 2019 06:47:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8952C216E3 for ; Thu, 4 Jul 2019 06:47:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727365AbfGDGrx (ORCPT ); Thu, 4 Jul 2019 02:47:53 -0400 Received: from mga05.intel.com ([192.55.52.43]:20588 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725879AbfGDGrw (ORCPT ); Thu, 4 Jul 2019 02:47:52 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga105.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 03 Jul 2019 23:47:51 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.63,449,1557212400"; d="scan'208";a="339525582" Received: from hao-dev.bj.intel.com (HELO localhost) ([10.238.157.65]) by orsmga005.jf.intel.com with ESMTP; 03 Jul 2019 23:47:49 -0700 Date: Thu, 4 Jul 2019 14:31:06 +0800 From: Wu Hao To: Greg KH Cc: Moritz Fischer , linux-fpga@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Zhang Yi Z , Xu Yilun , Alan Tull Subject: Re: [PATCH 06/15] fpga: dfl: fme: add DFL_FPGA_FME_PORT_RELEASE/ASSIGN ioctl support. Message-ID: <20190704063106.GA24777@hao-dev> References: <20190628004951.6202-1-mdf@kernel.org> <20190628004951.6202-7-mdf@kernel.org> <20190703180753.GA24723@kroah.com> <20190703233058.GA15825@hao-dev> <20190704053927.GB347@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190704053927.GB347@kroah.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 04, 2019 at 07:39:27AM +0200, Greg KH wrote: > On Thu, Jul 04, 2019 at 07:30:58AM +0800, Wu Hao wrote: > > On Wed, Jul 03, 2019 at 08:07:53PM +0200, Greg KH wrote: > > > On Thu, Jun 27, 2019 at 05:49:42PM -0700, Moritz Fischer wrote: > > > > From: Wu Hao > > > > > > > > In order to support virtualization usage via PCIe SRIOV, this patch > > > > adds two ioctls under FPGA Management Engine (FME) to release and > > > > assign back the port device. In order to safely turn Port from PF > > > > into VF and enable PCIe SRIOV, it requires user to invoke this > > > > PORT_RELEASE ioctl to release port firstly to remove userspace > > > > interfaces, and then configure the PF/VF access register in FME. > > > > After disable SRIOV, it requires user to invoke this PORT_ASSIGN > > > > ioctl to attach the port back to PF. > > > > > > > > Ioctl interfaces: > > > > * DFL_FPGA_FME_PORT_RELEASE > > > > Release platform device of given port, it deletes port platform > > > > device to remove related userspace interfaces on PF, then > > > > configures PF/VF access mode to VF. > > > > > > > > * DFL_FPGA_FME_PORT_ASSIGN > > > > Assign platform device of given port back to PF, it configures > > > > PF/VF access mode to PF, then adds port platform device back to > > > > re-enable related userspace interfaces on PF. > > > > > > Why are you not using the "generic" bind/unbind facility that userspace > > > already has for this with binding drivers to devices? Why a special > > > ioctl? > > > > Hi Greg, > > > > Actually we think it should be safer that making the device invisble than > > just unbinding its driver. Looks like user can try to rebind it at any > > time and we don't have any method to stop them. > > Why do you want to "stop" the user from doing something? They asked to > do it, why prevent it? If they ask to do something foolish, well, they > get to keep the pieces :) Actually this is for SRIOV support, as we are moving FPGA accelerator from PF to VF, so we don't want users to see the FPGA accelerator from PF any more. We can't allow user to touch same FPGA accelerator from both PF and VF side (it leads to hardware erros). > > > > > --- a/include/uapi/linux/fpga-dfl.h > > > > +++ b/include/uapi/linux/fpga-dfl.h > > > > @@ -176,4 +176,36 @@ struct dfl_fpga_fme_port_pr { > > > > > > > > #define DFL_FPGA_FME_PORT_PR _IO(DFL_FPGA_MAGIC, DFL_FME_BASE + 0) > > > > > > > > +/** > > > > + * DFL_FPGA_FME_PORT_RELEASE - _IOW(DFL_FPGA_MAGIC, DFL_FME_BASE + 1, > > > > + * struct dfl_fpga_fme_port_release) > > > > + * > > > > + * Driver releases the port per Port ID provided by caller. > > > > + * Return: 0 on success, -errno on failure. > > > > + */ > > > > +struct dfl_fpga_fme_port_release { > > > > + /* Input */ > > > > + __u32 argsz; /* Structure length */ > > > > + __u32 flags; /* Zero for now */ > > > > + __u32 port_id; > > > > +}; > > > > > > meta-comment, why do all of your structures for ioctls have argsz? You > > > "know" the size of the structure already, it's part of the ioctl > > > definition. You shouldn't need to also set it again, right? Otherwise > > > ALL Linux ioctls would need something crazy like this. > > > > Actually we followed the same method as vfio. > > vfio is a protocol on "the wire", right? Not an ioctl. > > > The major purpose should be extendibility, as we really need this to > > be sth long term maintainable. > > You can't change ioctl structure sizes at any time. > > > It really helps, if we add some new members for extentions/enhancement > > under the same ioctl. > > You don't do that. > > > I don't think everybody needs this, but my consideration here is if > > newer generations of hardware/specs come with some extentions, I still > > hope we can resue these IOCTLs as much as we could, instead of > > creating more new ones. > > You create new ones, like everyone else does, as you can not change old > code. By trying to "version" structures like this, it's just going to > be a nightmare. Actually i learned this from vfio code here, it's not trying to "version" structures, let me copy the comments from vfio header file. It should be more clear than above short description from me. "include/uapi/linux/vfio.h" /* * The IOCTL interface is designed for extensibility by embedding the * structure length (argsz) and flags into structures passed between * kernel and userspace. We therefore use the _IO() macro for these * defines to avoid implicitly embedding a size into the ioctl request. * As structure fields are added, argsz will increase to match and flag * bits will be defined to indicate additional fields with valid data. * It's *always* the caller's responsibility to indicate the size of * the structure passed by setting argsz appropriately. */ For example. struct vfio_device_info { __u32 argsz; __u32 flags; #define VFIO_DEVICE_FLAGS_RESET (1 << 0) /* Device supports reset */ #define VFIO_DEVICE_FLAGS_PCI (1 << 1) /* vfio-pci device */ #define VFIO_DEVICE_FLAGS_PLATFORM (1 << 2) /* vfio-platform device */ #define VFIO_DEVICE_FLAGS_AMBA (1 << 3) /* vfio-amba device */ #define VFIO_DEVICE_FLAGS_CCW (1 << 4) /* vfio-ccw device */ #define VFIO_DEVICE_FLAGS_AP (1 << 5) /* vfio-ap device */ __u32 num_regions; /* Max region index + 1 */ __u32 num_irqs; /* Max IRQ index + 1 */ Hope things could be more clear now. :) Thanks Hao }; > > thanks, > > greg k-h