Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755147Ab2JRJ3j (ORCPT ); Thu, 18 Oct 2012 05:29:39 -0400 Received: from mail-vc0-f174.google.com ([209.85.220.174]:64224 "EHLO mail-vc0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752654Ab2JRJ3M convert rfc822-to-8bit (ORCPT ); Thu, 18 Oct 2012 05:29:12 -0400 MIME-Version: 1.0 In-Reply-To: <507FA595.4020507@freescale.com> References: <1350538335-29026-1-git-send-email-b32955@freescale.com> <1350541111.5263.3.camel@vkoul-udesk3> <507FA595.4020507@freescale.com> Date: Thu, 18 Oct 2012 14:59:10 +0530 Message-ID: Subject: Re: [PATCH] dma: add new DMA control commands From: Jassi Brar To: Huang Shijie Cc: Vinod Koul , marex@denx.de, Huang Shijie , alsa-devel@alsa-project.org, shawn.guo@linaro.org, linux@arm.linux.org.uk, tiwai@suse.de, artem.bityutskiy@linux.intel.com, broonie@opensource.wolfsonmicro.com, linux-mmc@vger.kernel.org, w.sang@pengutronix.de, perex@perex.cz, linux-mtd@lists.infradead.org, linux-i2c@vger.kernel.org, ben-linux@fluff.org, djbw@fb.com, khali@linux-fr.org, cjb@laptop.org, dwmw2@infradead.org, lrg@ti.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset=GB2312 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1330 Lines: 32 On 18 October 2012 12:15, Huang Shijie wrote: > ?? 2012??10??18?? 14:18, Vinod Koul ะด??: > >> Why cant you do start (prepare clock etc) when you submit the descriptor >> to dmaengine. Can be done in tx_submit callback. >> Similarly remove the clock when dma transaction gets completed. > > I ever thought this method too. > > But it will become low efficient in the following case: > > Assuming the gpmi-nand driver has to read out 1024 pages in one _SINGLE_ > read operation. > The gpmi-nand will submit the descriptor to dmaengine per page. So with your > method, > the system will repeat the enable/disable dma clock 1024 time. At every > enable/disable dma clock, > the system has to enable the clock chain and it's parents ... > > But with this patch, we only need to enable/disable dma clock one time, just > at we select the nand chip. > If the clock is the dmac's property (not channels'), the toggling seems too aggressive. You could try using runtime_suspend/resume for clock disabling/enabling. How about employing autosuspend with a few ms delay? -- 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/