From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 60683C433DF for ; Fri, 5 Jun 2020 13:20:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 383E0206E6 for ; Fri, 5 Jun 2020 13:20:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591363242; bh=8BjtpV0ecJEgsvWK1ul8PsDdqfyLu30JW/S3Yqv/vGM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=hKIXV9Jhu7qmlZU0gzDBY7ma5msOLONaN+6I0sYlSHavQ4OxLdm/Ck1fXt4eBUswb 72wSWHmh8jgZHFhFx+2yNQj8/4vszi+f/V/PMDL6SxDWZEYu7Nx8OVfRL4Ml/HRrBY wei1/h6Gxx+RdD8vNNz6DtdO9RzCFHQ4m+kGo8Nc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726988AbgFENUl (ORCPT ); Fri, 5 Jun 2020 09:20:41 -0400 Received: from mail.kernel.org ([198.145.29.99]:38776 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726711AbgFENUk (ORCPT ); Fri, 5 Jun 2020 09:20:40 -0400 Received: from localhost (fw-tnat.cambridge.arm.com [217.140.96.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7F5F12065C; Fri, 5 Jun 2020 13:20:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591363240; bh=8BjtpV0ecJEgsvWK1ul8PsDdqfyLu30JW/S3Yqv/vGM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=1v1uwO8oSoExJnTbaNzm0VXW7Zl1MvMc119/QvOAbE7qh1tXndCPo0BkPisP1ReJR v7/OIXvCo7vyHQe1J1N/w1iEq8jqKHFD95mSV18DIj+OArLVfblrmtiKQIGCVkIGoL BZyOkkIORbn8a1ip7RS/L5YtOlIIkC2KHPcpHXTE= Date: Fri, 5 Jun 2020 14:20:37 +0100 From: Mark Brown To: Robin Murphy Cc: Florian Fainelli , linux-kernel@vger.kernel.org, "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Scott Branden , lukas@wunner.de, Ray Jui , Rob Herring , "open list:SPI SUBSYSTEM" , "maintainer:BROADCOM BCM281XX/BCM11XXX/BCM216XX ARM ARCHITE..." , "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" , Martin Sperl , Nicolas Saenz Julienne Subject: Re: [PATCH v2] spi: bcm2835: Enable shared interrupt support Message-ID: <20200605132037.GF5413@sirena.org.uk> References: <20200604212819.715-1-f.fainelli@gmail.com> <142d48ae-2725-1368-3e11-658449662371@arm.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="+jhVVhN62yS6hEJ8" Content-Disposition: inline In-Reply-To: <142d48ae-2725-1368-3e11-658449662371@arm.com> X-Cookie: Air is water with holes in it. User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --+jhVVhN62yS6hEJ8 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Fri, Jun 05, 2020 at 12:34:36PM +0100, Robin Murphy wrote: > On 2020-06-04 22:28, Florian Fainelli wrote: > > For the BCM2835 case which is deemed performance critical, we would like > > to continue using an interrupt handler which does not have the extra > > comparison on BCM2835_SPI_CS_INTR. > FWIW, if I'm reading the patch correctly, then with sensible codegen that > "overhead" should amount to a bit test on a live register plus a not-taken > conditional branch - according to the 1176 TRM that should add up to a > whopping 2 cycles. If that's really significant then I'd have to wonder > whether you want to be at the mercy of the whole generic IRQ stack at all, > and should perhaps consider using FIQ instead. Yes, and indeed the compiler does seem to manage that. It *is* non-zero overhead though. --+jhVVhN62yS6hEJ8 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAABCgAdFiEEreZoqmdXGLWf4p/qJNaLcl1Uh9AFAl7aRqQACgkQJNaLcl1U h9DI1Qf/Tz5aGiXqtwU/k3+gw6+ficRLOe7pkUSPRyQIDVciDPUy7ytsm0jw29uw 8SGzHF424tB65sfcrF+DHOEYXQRxMhKGJfZgQlPpENPIzuN/6keGkfQ9F8iNgUHe e8yOJRLUXEte7TB+5GOmQJnFY3prtrRTIE6nl3NJaOiO7zoX87nVXAJmt/+scwjm /RPUYi1A76q3Wj8ntaakVEyxYG1G6tKk8Fq9UF8AfTiQ0MC2EZmfzd/refGIJfD8 L2QTTwMIB7erragBJbjTX9alKe3/qkYlSS27+HGIg/HC+P2mODP9hJg67ZqLVPPr AeJLVJyfEzBWbzeii15aKq82J0fXsw== =aGmF -----END PGP SIGNATURE----- --+jhVVhN62yS6hEJ8--