Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756769AbaD1U7c (ORCPT ); Mon, 28 Apr 2014 16:59:32 -0400 Received: from mho-03-ewr.mailhop.org ([204.13.248.66]:34132 "EHLO mho-01-ewr.mailhop.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1756525AbaD1U73 (ORCPT ); Mon, 28 Apr 2014 16:59:29 -0400 X-Mail-Handler: Dyn Standard SMTP by Dyn X-Originating-IP: 96.249.243.124 X-Report-Abuse-To: abuse@dyndns.com (see http://www.dyndns.com/services/sendlabs/outbound_abuse.html for abuse reporting information) X-MHO-User: U2FsdGVkX18OhbwwJolK3d56+5WZ8/yACVvN6mOTBIM= X-DKIM: OpenDKIM Filter v2.0.1 titan D3C9556671F Date: Mon, 28 Apr 2014 16:59:11 -0400 From: Jason Cooper To: Sebastian Hesselbarth Cc: Thomas Gleixner , Andrew Lunn , Gregory Clement , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH RESEND 3/3] irqchip: orion: reverse irq handling priority Message-ID: <20140428205911.GC28159@titan.lakedaemon.net> References: <1398540855-27367-1-git-send-email-sebastian.hesselbarth@gmail.com> <1398540855-27367-4-git-send-email-sebastian.hesselbarth@gmail.com> <535EB4C1.9090603@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <535EB4C1.9090603@gmail.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 28, 2014 at 10:06:25PM +0200, Sebastian Hesselbarth wrote: > On 04/28/2014 09:39 PM, Thomas Gleixner wrote: > > On Sat, 26 Apr 2014, Sebastian Hesselbarth wrote: > > > >> Non-DT irq handlers were working through irq causes from most-significant > >> to least-significant bit, while DT irqchip driver does it the other way > >> round. This revealed some more HW issues on Kirkwood peripheral IP, where > >> spurious sdio irqs can happen although IP's irq enable registers are all > >> zero. Although, not directly related with the described issue, reverse > >> irq bit handling back to original order by replacing ffs() with fls(). > > > > So why are we reverting to the original order? > > > > The explanation above is just confusing. > > Actually, I first wanted to reply "The original order worked for > years, so get back to it." But then I thought about finding a better > answer and remembered some comment of Russell a while ago. > > I disassembled the generated binary and the original order saves two > instructions for each bit count using clz. > > With this patch: > 60: e3a07001 mov r7, #1 > 64: e16f3f14 clz r3, r4 > 68: e263301f rsb r3, r3, #31 > 6c: e1c44317 bic r4, r4, r7, lsl r3 > 70: e5951004 ldr r1, [r5, #4] > > Without this patch: > 60: e3a06001 mov r6, #1 > 64: e2643000 rsb r3, r4, #0 > 68: e0033004 and r3, r3, r4 > 6c: e16f3f13 clz r3, r3 > 70: e263301f rsb r3, r3, #31 > 74: e1c44316 bic r4, r4, r6, lsl r3 > 78: e5971004 ldr r1, [r7, #4] > You want me to reword the commit message accordingly? Please do. I would even quote the above. thx, Jason. -- 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/