Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756606Ab3JHXrr (ORCPT ); Tue, 8 Oct 2013 19:47:47 -0400 Received: from mail-bk0-f42.google.com ([209.85.214.42]:50182 "EHLO mail-bk0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755789Ab3JHXrn (ORCPT ); Tue, 8 Oct 2013 19:47:43 -0400 MIME-Version: 1.0 In-Reply-To: <20131008214401.GC11941@kroah.com> References: <20131003064915.GB17155@amd.pavel.ucw.cz> <524EC965.70701@monstr.eu> <20131004141646.GA9396@kroah.com> <524ED081.1040600@monstr.eu> <524EF0CE.4040002@zytor.com> <524EFE76.70200@monstr.eu> <524F04FD.5020804@zytor.com> <20131004233341.GA4028@kroah.com> <1381251614.6062.9.camel@atx-linux-37> <20131008214401.GC11941@kroah.com> Date: Tue, 8 Oct 2013 18:47:41 -0500 Message-ID: Subject: Re: [RFC PATCH v2 0/1] FPGA subsystem core From: delicious quinoa To: Greg Kroah-Hartman Cc: Alan Tull , "H. Peter Anvin" , monstr@monstr.eu, Pavel Machek , Michal Simek , linux-kernel@vger.kernel.org, Dinh Nguyen , Philip Balister , Alessandro Rubini , Steffen Trumtrar , Jason Gunthorpe , Jason Cooper , Yves Vandervennet , Kyle Teske , Josh Cartwright , Nicolas Pitre , Mark Langsdorf , Felipe Balbi , linux-doc@vger.kernel.org, Mauro Carvalho Chehab , David Brown , Rob Landley , "David S. Miller" , Joe Perches , Cesar Eduardo Barros , Samuel Ortiz , Andrew Morton Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4164 Lines: 95 On Tue, Oct 8, 2013 at 4:44 PM, Greg Kroah-Hartman wrote: > On Tue, Oct 08, 2013 at 12:00:14PM -0500, Alan Tull wrote: >> On Fri, 2013-10-04 at 16:33 -0700, Greg Kroah-Hartman wrote: >> > On Fri, Oct 04, 2013 at 11:12:13AM -0700, H. Peter Anvin wrote: >> > > On 10/04/2013 10:44 AM, Michal Simek wrote: >> > > > >> > > > If you look at it in general I believe that there is wide range of >> > > > applications which just contain one bitstream per fpga and the >> > > > bitstream is replaced by newer version in upgrade. For them >> > > > firmware interface should be pretty useful. Just setup firmware >> > > > name with bitstream and it will be automatically loaded in startup >> > > > phase. >> > > > >> > > > Then there is another set of applications especially in connection >> > > > to partial reconfiguration where this can be done statically by >> > > > pregenerated partial bitstreams or automatically generated on >> > > > target cpu. For doing everything on the target firmware interface >> > > > is not the best because everything can be handled by user >> > > > application and it is easier just to push this bitstream to do >> > > > device and not to save it to the fs. >> > > > >> > > > I think the question here is if this subsystem could have several >> > > > interfaces. For example Alan is asking for adding char support. >> > > > Does it even make sense to have more interfaces with the same >> > > > backend driver? When this is answered then we can talk which one >> > > > make sense to have. In v2 is sysfs and firmware one. Adding char >> > > > is also easy to do. >> > > > >> > > >> > > Greg, what do you think? >> > > >> > > I agree that the firmware interface makes sense when the use of the >> > > FPGA is an implementation detail in a fixed hardware configuration, >> > > but that is a fairly restricted use case all things considered. >> > >> > Ideally I thought this would be just like "firmware", you dump the file >> > to the FPGA, it validates it and away you go with a new image running in >> > the chip. >> > >> > But, it sounds like this is much more complicated, so much so that >> > configfs might be the correct interface for it, as you can do lots of >> > things there, and it is very flexible (some say too flexible...) >> > >> > A char device, with a zillion different custom ioctls is also a way to >> > do it, but one that I really want to avoid as that gets messy really >> > quickly. >> >> Hi Greg, >> >> We are discussing a char device that has very few interfaces: >> - a way of writing the image to fpga >> - a way of getting fpga manager status >> - a way of setting fpga manager state >> >> This all looks like standard char driver interface to me. Writing the >> image could be writing to the devnode (cat image.bin > /dev/fpga0). The >> status stuff would be sysfs attributes. All normal stuff any char >> driver in the kernel would do. Why not just go with that? > > Because we really hate to add new ioctls to the kernel if at all > possible. I don't see any need for adding any ioctls. > Using sysfs (and it's one-value-per-file rule), makes > userspace tools easier, and managing the different devices in the system > easier (you know _exactly_ which device you are talking to, you don't > have to guess based on minor number). That's cool. The interface we could use is writing the raw fpga data to /sys/class/fpga_manager/fpga0/fpga_config_data Reading or setting the fpga state could be from /sys/class/fpga_manager/fpga0/fpga_config_state Or do I misunderstand? Do you include sysfs attributes when you are talking about ioctls? Alan > > thanks, > > greg k-h > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/