From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754776AbZHKOPI (ORCPT ); Tue, 11 Aug 2009 10:15:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754709AbZHKOPG (ORCPT ); Tue, 11 Aug 2009 10:15:06 -0400 Received: from waldorf.bytemark.co.uk ([212.110.162.22]:42476 "EHLO waldorf.bytemark.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753181AbZHKOPF (ORCPT ); Tue, 11 Aug 2009 10:15:05 -0400 Date: Tue, 11 Aug 2009 11:40:25 +0200 From: "Emilio G. Cota" To: Martyn Welch Cc: Greg K-H , linux-kernel@vger.kernel.org, devel@driverdev.osuosl.org, Sebastien Dugue Subject: Re: [patch 2/5] Staging: vme: add VME userspace driver Message-ID: <20090811094025.GC3251@braap.org> References: <20090803205657.964064732@mini.kroah.org> <20090803210116.GC28430@kroah.com> <20090808232259.GA29303@braap.org> <20090809121715.GA3884@braap.org> <4A801D04.6050102@gefanuc.com> <20090810152606.GA23319@braap.org> <4A804B0B.5020809@gefanuc.com> <20090810203637.GD3055@braap.org> <4A8133ED.6070304@gefanuc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4A8133ED.6070304@gefanuc.com> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Martyn Welch wrote: > suggest if you want something more complex that allows the user to just > pick a location/size and not worry about windows at all That's exactly the whole point. I think each bridge should manage its resources; putting this on the upper layer would mean the layer should have a mechanism of 'discovering' what the bridge can/can't do. Anyway this could be revisited later. I'm preparing a patch for this. >> - Most accesses are 32-bit accesses. Treating all of them >> as 64-bit accesses would decrease performance for most of >> them--which happen to be 32-bit. > I'm not - I'm storing them as 64-bit values, which they are, in the > structures used in *software*. These are then split *when* a write to > the hardware registers is required. Similarly, when the registers are > occasionally read they are combined and stored as a 64-bit value. This > simplifies all *software* checking and manipulation. By storing these as > 2 32-bit values every driver that uses the VME core will need to convert > pci addresses, vme addresses and counts to 2 32-bit values. That is > madness. I agree with you on that's painful for doing 64-bit accesses. However I'm still not convinced on the performance side (I mean software), since most of the time the upper 32bits will be empty. Will have a look though. Cheers, E.