Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758458AbbGHNle (ORCPT ); Wed, 8 Jul 2015 09:41:34 -0400 Received: from mx0b-00176a03.pphosted.com ([67.231.157.48]:52080 "EHLO mx0b-00176a03.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753749AbbGHNlb (ORCPT ); Wed, 8 Jul 2015 09:41:31 -0400 Message-ID: <559D2879.30602@ge.com> Date: Wed, 8 Jul 2015 14:41:13 +0100 From: Martyn Welch User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Alessio Igor Bogani , Dmitry Kalinkin CC: , Greg Kroah-Hartman , Igor Alekseev , LKML , Manohar Vanga Subject: Re: [PATCHv3 08/16] staging: vme_user: provide DMA functionality References: <1432814833-5320-1-git-send-email-dmitry.kalinkin@gmail.com> <1432814833-5320-9-git-send-email-dmitry.kalinkin@gmail.com> <20150613002807.GA17459@kroah.com> <559A8117.4060701@ge.com> <559A9556.4040303@ge.com> <78FC1849-FFE4-49E5-8421-25D27324F790@gmail.com> In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [3.159.19.193] X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2015-07-08_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1506180000 definitions=main-1507080215 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1816 Lines: 36 On 07/07/15 13:51, Alessio Igor Bogani wrote: >> Current VME stack links windows not to the boards, but to device drivers. >> >Driver >> >could potentially minimise window usage within it’s scope (any sort of >> >window >> >reusing, like mapping whole A16 once to be used with all boards), but this >> >won’t >> >work across multiple drivers. Even if all of your drivers are window-wise >> >economic, >> >they will still need some amount of windows per each driver. Not that we >> >have that >> >many kernel drivers... > Yes you can share a window/image between all boards of the same type > (in effect we are porting our drivers in this way)*but* it isn't the > expected way to work (see Documentation/vme_api.txt struct > vme_driver's probe() and match() functions and the GE PIO2 VME > driver). I think it's perfectly valid to use a single window to dynamically map to the address space belonging to one of a number of devices supported by a single driver. I think this is almost preferable to mapping a large window over a large portion of the VME address space to drive a number of devices as (depending on there spacing in the VME address space) the latter could cause issues with filling available PCI address space. Admittedly this is more of a problem on 32-bit systems, but... -- Martyn Welch (Lead Software Engineer) | Registered in England and Wales GE Intelligent Platforms | (3828642) at 100 Barbirolli Square T +44(0)1327322748 | Manchester, M2 3AB E martyn.welch@ge.com | VAT:GB 927559189 -- 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/