From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753556AbbAUUcj (ORCPT ); Wed, 21 Jan 2015 15:32:39 -0500 Received: from mail-wg0-f52.google.com ([74.125.82.52]:48033 "EHLO mail-wg0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751938AbbAUUcc convert rfc822-to-8bit (ORCPT ); Wed, 21 Jan 2015 15:32:32 -0500 Subject: Re: [PATCH v8 2/4] fpga manager: add sysfs interface document Mime-Version: 1.0 (Mac OS X Mail 8.1 \(1993\)) Content-Type: text/plain; charset=utf-8 From: Pantelis Antoniou In-Reply-To: <20150121202700.GB4942@obsidianresearch.com> Date: Wed, 21 Jan 2015 22:32:23 +0200 Cc: One Thousand Gnomes , atull , Greg Kroah-Hartman , Pavel Machek , hpa@zytor.com, Michal Simek , Michal Simek , Randy Dunlap , Linux Kernel Mailing List , devicetree@vger.kernel.org, robh+dt@kernel.org, Grant Likely , iws@ovro.caltech.edu, linux-doc@vger.kernel.org, Mark Brown , philip@balister.org, rubini@gnudd.com, Steffen Trumtrar , jason@lakedaemon.net, kyle.teske@ni.com, nico@linaro.org, Felipe Balbi , m.chehab@samsung.com, davidb@codeaurora.org, Rob Landley , davem@davemloft.net, cesarb@cesarb.net, sameo@linux.intel.com, Andrew Morton , Linus Walleij , pawel.moll@arm.com, mark.rutland@arm.com, ijc+devicetree@hellion.org.uk, galak@codeaurora.org, devel@driverdev.osuosl.org, Alan Tull , dinguyen@opensource.altera.com, yvanderv@opensource.altera.com Content-Transfer-Encoding: 8BIT Message-Id: <7E60D554-8660-4CDB-BF68-D39DD29039BE@konsulko.com> References: <20150113162847.2778b5a5@lxorguk.ukuu.org.uk> <20150113200032.GA16205@obsidianresearch.com> <20150113222450.GA17475@obsidianresearch.com> <20150115184726.GA23247@obsidianresearch.com> <20150115204502.591bca1d@lxorguk.ukuu.org.uk> <20150121160151.453ba403@lxorguk.ukuu.org.uk> <20150121202700.GB4942@obsidianresearch.com> To: Jason Gunthorpe X-Mailer: Apple Mail (2.1993) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Jason, > On Jan 21, 2015, at 22:27 , Jason Gunthorpe wrote: > > On Wed, Jan 21, 2015 at 06:33:12PM +0200, Pantelis Antoniou wrote: >> Hi Alan, >> >>> On Jan 21, 2015, at 18:01 , One Thousand Gnomes wrote: >>> >>> On Thu, 15 Jan 2015 22:54:46 +0200 >>> Pantelis Antoniou wrote: >>> >>>> Hi Alan, >>>> >>>>> On Jan 15, 2015, at 22:45 , One Thousand Gnomes wrote: >>>>> >>>>> On Thu, 15 Jan 2015 11:47:26 -0700 >>>>> Jason Gunthorpe wrote: >>>>>> It is a novel idea, my concern would be that embedding the FPGA in the >>>>>> DT makes it permanent unswappable kernel memory. >>>>>> Not having the kernel hold the FPGA is best for many uses. >>>>> >>>>> If you have a filesysytem before the FPGA is set up then it belongs in >>>>> the file system. As you presumably loaded the kernel from somewhere there >>>>> ought to be a file system (even an initrd). >>>>> >>>> >>>> Request firmware does not imply keeping it around. You can always re-request >>>> when reloading (although there’s a nasty big of caching that needs to be >>>> resolved with the firmware loader). >>> >>> Which comes down to the same thing. Unless you can prove that there is a >>> path to recover the firmware file that does not have any dependancies >>> upon the firmware executing (and those can be subtle and horrid at times) >>> you need to keep it around for suspend/resume at least and potentially >>> any unexpected error/reset. >>> >> >> In that case the only safe place to put it is in the kernel image itself, which >> is something the firmware loader already supports. > > My point is that the current firmware layer is overly cautious and > FPGAs are very big. My current project on small Xilinx device has a > 10MB programming file. The biggest Xilinx device today has a max > bitfile size around 122MB. > > So keeping that much memory pinned in the kernel when I can prove it > is uncessary for my system (either because there is no suspend/resume > possibility, or because I know the CPU can always access the > filesytem) is very undesirable. > > Other systems might have to take the ram hit. > > Since it seems like the kernel has no way to know, we probably have > have a way to tell it not to cache the bitfile. > The firmware loader was not originally meant to handle these cases, but I’m sure it’s not an insurmountable obstacle. > Jason Regards — Pantelis