Linus, Thanks for the pointers. > -----Original Message----- > From: Linus Walleij [mailto:linus.walleij@xxxxxxxxxx] > Sent: Monday, June 13, 2011 7:43 PM > To: Raju, Sundaram > Cc: Russell King - ARM Linux; Koul, Vinod; Dan; davinci-linux-open- > source@xxxxxxxxxxxxxxxxxxxx; linux-omap@xxxxxxxxxxxxxxx; linux- > kernel@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > Subject: Re: [RFC] dmaengine: add new api for preparing simple slave transfer > > On Fri, Jun 10, 2011 at 3:33 PM, Russell King - ARM Linux > <linux@xxxxxxxxxxxxxxxx> 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 transferred, > > M following bytes to be skipped, N bytes to be transferred, M bytes to be > > skipped. I doubt there are many controllers which can be programmed 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 = { > take = M, > skip = N, > }; > > ret = chan->device->device_control(chan, SDMA_TEXAS_STRIDE_CONFIG, > &sdma_ti_stride_cfg); > > Or something like this. Yes, the hardware can skip over sequences like that. I also thought about your suggestion, at first before submitting the RFC. But I dint pursue this because, this ioctl() call has to be made before every single prepare call. I may have to end up using this if we decide not to change the API signature for prepare APIs. I actually intend to use this for all DMAC related ioctl(). Configuring the DMAC and programming various modes etc specific to the DMAC. I suppose this is the only way to do it. Let me know if there is any other way to do it. Thanks, Sundaram -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
