From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755641AbbJVIPK (ORCPT ); Thu, 22 Oct 2015 04:15:10 -0400 Received: from mout.kundenserver.de ([212.227.126.131]:52446 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750989AbbJVIPA (ORCPT ); Thu, 22 Oct 2015 04:15:00 -0400 From: Arnd Bergmann To: linux-arm-kernel@lists.infradead.org Cc: Kedareswara rao Appana , anirudh@xilinx.com, wg@grandegger.com, mkl@pengutronix.de, michal.simek@xilinx.com, soren.brinkmann@xilinx.com, appanad@xilinx.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-can@vger.kernel.org Subject: Re: [PATCH 1/2] can: xilinx: use readl/writel instead of ioread/iowrite Date: Thu, 22 Oct 2015 10:14:30 +0200 Message-ID: <4061693.oBld7AKBIp@wuerfel> User-Agent: KMail/4.11.5 (Linux/3.16.0-10-generic; KDE/4.11.5; x86_64; ; ) In-Reply-To: <1445489163-11045-1-git-send-email-appanad@xilinx.com> References: <1445489163-11045-1-git-send-email-appanad@xilinx.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-Provags-ID: V03:K0:TEDHnMHZyJX73gLVT4H9NzabwcDPyiQZCmB2aM+lwPEY2iTU5+Y 4OYWGbR7ZAWHYw3GjSMG+tfIvFLp9wnXxutUptRxTEbdVzStVrmjIOzoTfTTiAAwRRUfQT9 q5RiDcMYOznpmdDY/d2/Eo3CZPlX/wbuT3vPfrfkOfb5ss/zxWFGn40231sM22e9R5R+urY hSrE/INUj/6/f5/Va0rcw== X-UI-Out-Filterresults: notjunk:1;V01:K0:lZTaFRu6BnY=:IBQXYqflkANqOdAAvhh9Eu BGtGGyEx6mSgOsn5tFZkcBXffXnm4dSwBhxTPcFu/FaAZwLBXx+oJ5/0KDssbZQy7K3Ji1fln FjbAIpwf8WQkSV7fraUFpBGU6U6lIIwoOPKma84AK+Yeep2epU2KU9WSukt7vHDS2jkb8HKyA XZu+qqWqhtL1VTKHfdI1x8C0lswrwdj8gLCQ0CA9mNzbPanwH0IYGTIReF13bl4pf6J20/c73 ytbZpTsMoy0DIHlMKOn5a6xtNKT4hNKBkLI/E79nIf3+d6xA36K+JLErOIRziXaooIwz0g6+A 6w+5NDD+CDox0pfiZPq/fziSGadW70haJnSznxoXisAyTjUNIgqqKHsNCdvg1M/G8hs2POhNk UbYIZSrV6wrWLPTurK1kQPL4I45kOmMXEqyVZMUwTwj0U7X6VX5kfoD3Du84TzllPXrEpV5zB gZOr6874g8zrmdv43eeQO5g2iIUoWg4DmbO0YoIVpD+bfMXKs5MDnQtOaPqiQMG5zjjp4Rjuq cUyLvU6Z/A3GY71rAbSLXSMGDRXMV5zVi23I6Fk3DAzfry99NPK7X15yZc/TipWdH21N05JcK DsYX8jONW7c5NZICkZqRWuCdN+zhiCRMCiFrqyYc4BLoprb0mH8elv3cN9lm0P/MxDzdRx0oh sgBdSq4xwRPKTa6Mc1HVna29vrkQuuAU5G+hBlfYaluBMMmxetXBnvIbacBI29dXjfud0v7uF j+83lu+qR6JKomiq Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thursday 22 October 2015 10:16:02 Kedareswara rao Appana wrote: > The driver only supports memory-mapped I/O [by ioremap()], > so readl/writel is actually the right thing to do, IMO. > During the validation of this driver or IP on ARM 64-bit processor > while sending lot of packets observed that the tx packet drop with iowrite > Putting the barriers for each tx fifo register write fixes this issue > Instead of barriers using writel also fixed this issue. > > Signed-off-by: Kedareswara rao Appana The two should really do the same thing: iowrite32() is just a static inline calling writel() on both ARM32 and ARM64. On which kernel version did you observe the difference? It's possible that an older version used CONFIG_GENERIC_IOMAP, which made this slightly more expensive. If there are barriers that you want to get rid of for performance reasons, you should use writel_relaxed(), but be careful to synchronize them correctly with regard to DMA. It should be fine in this driver, as it does not perform any DMA, but be aware that there is no big-endian version of writel_relaxed() at the moment. Arnd