From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754842Ab2AEJTf (ORCPT ); Thu, 5 Jan 2012 04:19:35 -0500 Received: from ch1ehsobe006.messaging.microsoft.com ([216.32.181.186]:23782 "EHLO ch1outboundpool.messaging.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754202Ab2AEJTP (ORCPT ); Thu, 5 Jan 2012 04:19:15 -0500 X-SpamScore: -9 X-BigFish: VS-9(zz1432N98dKzz1202hzz8275dhz2dh2a8h668h839h944h) X-Forefront-Antispam-Report: CIP:70.37.183.190;KIP:(null);UIP:(null);IPV:NLI;H:mail.freescale.net;RD:none;EFVD:NLI Date: Thu, 5 Jan 2012 17:19:05 +0800 From: Richard Zhao To: Shawn Guo CC: Richard Zhao , Arnd Bergmann , , , , , , , Subject: Re: [PATCH v3 2/2] dma/imx-sdma: use writel to write register when enable a channel Message-ID: <20120105091904.GO2414@b20223-02.ap.freescale.net> References: <1325750362-22598-1-git-send-email-richard.zhao@linaro.org> <1325750362-22598-3-git-send-email-richard.zhao@linaro.org> <20120105092316.GB1729@S2101-09.ap.freescale.net> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20120105092316.GB1729@S2101-09.ap.freescale.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-OriginatorOrg: freescale.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Shawn, On Thu, Jan 05, 2012 at 05:23:17PM +0800, Shawn Guo wrote: > On Thu, Jan 05, 2012 at 03:59:22PM +0800, Richard Zhao wrote: > > dma_alloc_coherent memory may be bufferable when set > > CONFIG_ARM_DMA_MEM_BUFFERABLE. We need to add nececcary > > memory barrier. writel implicitly call wmb in such case. > > > > Signed-off-by: Richard Zhao > > --- > > drivers/dma/imx-sdma.c | 2 +- > > 1 files changed, 1 insertions(+), 1 deletions(-) > > > > diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c > > index c2bc4f1..e987468 100644 > > --- a/drivers/dma/imx-sdma.c > > +++ b/drivers/dma/imx-sdma.c > > @@ -396,7 +396,7 @@ static int sdma_config_ownership(struct sdma_channel *sdmac, > > > > static void sdma_enable_channel(struct sdma_engine *sdma, int channel) > > { > > - __raw_writel(1 << channel, sdma->regs + SDMA_H_START); > > + writel(1 << channel, sdma->regs + SDMA_H_START); > > } > > > > As educated by Arnd, generally it's safer to use pair of readl/writel > than __raw_readl/__raw_writel in driver. I'm wondering if it's a good > opportunity for us to change the pair all over this driver. Russel mentioned that too. But I cannot understand. If CONFIG_ARM_DMA_MEM_BUFFERABLE, readl/writel always call rmb/wmb. Do we realy need it? It might affect performance. Du to the concern, I didn't convert all the readl/writel. Thanks Richard > > -- > Regards, > Shawn > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >