From mboxrd@z Thu Jan 1 00:00:00 1970 From: Huang Shijie Subject: Re: [PATCH] dma: add new DMA control commands Date: Thu, 18 Oct 2012 17:10:46 +0800 Message-ID: <507FC796.7060401@freescale.com> References: <1350538335-29026-1-git-send-email-b32955@freescale.com> <1350541111.5263.3.camel@vkoul-udesk3> <507FA595.4020507@freescale.com> <20121018085208.GR21164@n2100.arm.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20121018085208.GR21164-l+eeeJia6m9vn6HldHNs0ANdhmdF6hFW@public.gmane.org> Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Russell King - ARM Linux Cc: Vinod Koul , djbw-b10kYP2dOMg@public.gmane.org, khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org, ben-linux-elnMNo+KYs3YtjvyW6yDsg@public.gmane.org, w.sang-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org, cjb-2X9k7bc8m7Mdnm+yROfE0A@public.gmane.org, dwmw2-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, lrg-l0cyMroinI0@public.gmane.org, broonie-yzvPICuk2AATkU/dhu1WVueM+bqZidxxQQ4Iyu8u01E@public.gmane.org, perex-/Fr2/VpizcU@public.gmane.org, tiwai-l3A5Bk7waGM@public.gmane.org, shawn.guo-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org, marex-ynQEQJNshbs@public.gmane.org, artem.bityutskiy-VuQAYsv1563Yd54FQh9/CA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mmc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mtd-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, alsa-devel-K7yf7f+aM1XWsZ/bQMPhNw@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Huang Shijie List-Id: linux-i2c@vger.kernel.org =E4=BA=8E 2012=E5=B9=B410=E6=9C=8818=E6=97=A5 16:52, Russell King - ARM= Linux =E5=86=99=E9=81=93: > On Thu, Oct 18, 2012 at 02:45:41PM +0800, Huang Shijie wrote: >> =E4=BA=8E 2012=E5=B9=B410=E6=9C=8818=E6=97=A5 14:18, Vinod Koul =E5=86= =99=E9=81=93: >>> Why cant you do start (prepare clock etc) when you submit the descr= iptor >>> 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 w= ith >> your method, >> the system will repeat the enable/disable dma clock 1024 time. At ev= ery >> enable/disable dma clock, >> the system has to enable the clock chain and it's parents ... > And what if you stop using clk_prepare_enable(), and prepare the cloc= k > when the channel is requested and only use clk_enable() in the tx_sub= mit yes. it's a little better. There is nearly no difference between the clk_prepare_enable() and=20 clk_enable() in actually. the clk_gate2_ops does not have any @->prepare. thanks Huang Shijie > method? >