From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751164AbeCICu4 (ORCPT ); Thu, 8 Mar 2018 21:50:56 -0500 Received: from shards.monkeyblade.net ([184.105.139.130]:46414 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750878AbeCICuy (ORCPT ); Thu, 8 Mar 2018 21:50:54 -0500 Date: Thu, 08 Mar 2018 21:50:53 -0500 (EST) Message-Id: <20180308.215053.1594215295032419362.davem@davemloft.net> To: niklas.cassel@axis.com Cc: peppe.cavallaro@st.com, alexandre.torgue@st.com, Jose.Abreu@synopsys.com, pavel@ucw.cz, niklass@axis.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net-next] net: stmmac: remove superfluous wmb() memory barriers From: David Miller In-Reply-To: <20180308103006.1197-1-niklas.cassel@axis.com> References: <20180308103006.1197-1-niklas.cassel@axis.com> X-Mailer: Mew version 6.7 on Emacs 25.3 / Mule 6.0 (HANACHIRUSATO) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Niklas Cassel Date: Thu, 8 Mar 2018 11:30:05 +0100 > These wmb() memory barriers are performed after the last descriptor write, > and they are followed by enable_dma_transmission()/set_tx_tail_ptr(), > i.e. a writel() to MMIO register space. > Since writel() itself performs the equivalent of a wmb() before doing the > actual write, these barriers are superfluous, and removing them should > thus not change any existing behavior. > > Ordering within the descriptor writes is already ensured with dma_wmb() > barriers inside prepare_tx_desc(first, ..)/prepare_tso_tx_desc(first, ..). > > Signed-off-by: Niklas Cassel Please allow me some time to consider this issue a little bit more before applying this patch. Thank you Niklas.