From owner-freebsd-current@freebsd.org Tue Apr 5 16:21:43 2016 Return-Path: Delivered-To: freebsd-current@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 0D482B044CE for ; Tue, 5 Apr 2016 16:21:43 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 824741105; Tue, 5 Apr 2016 16:21:42 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kostik@localhost [127.0.0.1]) by kib.kiev.ua (8.15.2/8.15.2) with ESMTPS id u35GLUo2076256 (version=TLSv1 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO); Tue, 5 Apr 2016 19:21:30 +0300 (EEST) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua u35GLUo2076256 Received: (from kostik@localhost) by tom.home (8.15.2/8.15.2/Submit) id u35GLUkO076255; Tue, 5 Apr 2016 19:21:30 +0300 (EEST) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Tue, 5 Apr 2016 19:21:29 +0300 From: Konstantin Belousov To: John Baldwin Cc: freebsd-current@freebsd.org, Ryan Stone Subject: Re: accessing a PCIe register from userspace through kmem or other ways ? Message-ID: <20160405162129.GG1741@kib.kiev.ua> References: <9376230.YZMFsgSvTf@ralph.baldwin.cx> <20160405061431.GF1741@kib.kiev.ua> <2874767.SJKfSzhn1q@ralph.baldwin.cx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2874767.SJKfSzhn1q@ralph.baldwin.cx> User-Agent: Mutt/1.5.24 (2015-08-30) X-Spam-Status: No, score=-2.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FREEMAIL_FROM,NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.1 X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on tom.home X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 05 Apr 2016 16:21:43 -0000 On Tue, Apr 05, 2016 at 08:55:54AM -0700, John Baldwin wrote: > Mostly I do not have experience with MGTDEVICE, though I was planning to > look at it as a way to implement this. Two things though: 1) there may > not be a cdev to associate with, and 2) I know of at least one device driver > that would use this in addition to using this for a general "map this BAR" > ioctl on /dev/pci. So /dev/pci is the natural cdev to place the functionality. An ioctl on /dev/pci may mmap BAR and return the base address. > There are other cases in the past where I used OBJT_SG > but would have preferred to use a variant that used managed pages so that > I could invidate any existing mappings. In particular what I want to do > is invalidate an object so that any future uses fail. > > Alternatively, it might be nice to hook a destructor call into a VM object > so that I could know when the object is no longer in use (knowing that all > its mappings have been destroyed). When using OBJT_SG objects as aliases > for other things (memory allocated via contigmalloc or bus_dma or for > resources like PCI BARs), I could keep a reference count on the original > "thing" that I increment when creating an OBJT_SG object to return from > something like d_mmap_single() or the /dev/pci ioctl and drop the reference > count in the destructor hook for that object. This is in essence how GEM objects + MGTDEVICE mappings work for i915. The only bottleneck in the API arrangement is that d_mmap_single() only gets the offset as the identifying data to construct the mapping. For /dev/pci, the offset parameter would need to encode d:b:s:f and BAR index.