From mboxrd@z Thu Jan 1 00:00:00 1970 From: Linus Walleij Subject: Re: [RFC] dmaengine: add new api for preparing simple slave transfer Date: Mon, 13 Jun 2011 16:13:15 +0200 Message-ID: References: <20110609124723.GA24636@n2100.arm.linux.org.uk> <20110609163206.GB24636@n2100.arm.linux.org.uk> <1307686397.10976.116.camel@vkoul-udesk3> <20110610104318.GC24636@n2100.arm.linux.org.uk> <20110610133338.GD24636@n2100.arm.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20110610133338.GD24636@n2100.arm.linux.org.uk> Sender: linux-kernel-owner@vger.kernel.org To: "Raju, Sundaram" Cc: Russell King - ARM Linux , "Koul, Vinod" , Dan , "davinci-linux-open-source@linux.davincidsp.com" , "linux-omap@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" List-Id: linux-omap@vger.kernel.org On Fri, Jun 10, 2011 at 3:33 PM, Russell King - ARM Linux wrote: > On Fri, Jun 10, 2011 at 05:18:46PM +0530, Raju, Sundaram wrote: >> Now DMACs capable of 3D transfer, do transfer of the whole 1D >> buffer per sync received or even whole 2D buffer per sync received >> (based on the sync rate programmed in the DMAC). > > The only issue which I see that we don't cover is the case where you = want > to describe a single buffer which is organised as N bytes to be trans= ferred, > M following bytes to be skipped, N bytes to be transferred, M bytes t= o be > skipped. =A0I doubt there are many controllers which can be programme= d with > both 'N' and 'M' parameters directly. Sundaram is this how your controller works? I mean the hardware can skip over sequences like this? When we added the config interface to DMAengine I originally included a "custom config" call, but Dan wanted me to keep it out until we had some specific usecase for it. FSLDMA recently started to use it. Notice how dmaengine_slave_config() is implemented: static inline int dmaengine_slave_config(struct dma_chan *chan, struct dma_slave_config *config) { return dmaengine_device_control(chan, DMA_SLAVE_CONFIG, (unsigned long)config); } So what is passed to the driver is just an unsigned long. This is actually modeled to be ioctl()-like so you can pass in a custom config to the same callback on the device driver, just use some other enumerator than DMA_SLAVE_CONFIG, say like FSLDMA already does with FSLDMA_EXTERNAL_START. Just put some enumerator in enum dma_ctrl_cmd in dmaengine.h such as SDMA_TEXAS_STRIDE_CONFIG and call like this: /* However that config struct needs to look, basically */ static struct sdma_ti_stride_cgf =3D { take =3D M, skip =3D N, }; ret =3D chan->device->device_control(chan, SDMA_TEXAS_STRIDE_CONFIG, &sdma_ti_stride_cfg); Or something like this. Thanks, Linus Walleij