From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <507FC796.7060401@freescale.com> Date: Thu, 18 Oct 2012 17:10:46 +0800 From: Huang Shijie MIME-Version: 1.0 To: Russell King - ARM Linux Subject: Re: [PATCH] dma: add new DMA control commands 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> In-Reply-To: <20121018085208.GR21164@n2100.arm.linux.org.uk> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: quoted-printable Cc: marex@denx.de, Huang Shijie , Vinod Koul , shawn.guo@linaro.org, alsa-devel@alsa-project.org, 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 List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , =E4=BA=8E 2012=E5=B9=B410=E6=9C=8818=E6=97=A5 16:52, Russell King - ARM L= inux =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 descrip= tor >>> 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 wit= h >> your method, >> the system will repeat the enable/disable dma clock 1024 time. At ever= y >> 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 clock > when the channel is requested and only use clk_enable() in the tx_submi= t 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? >