On Tue, May 02, 2017 at 03:16:18PM +0000, Eugeniy Paltsev wrote: > Hi Vinod, > > On Mon, 2017-05-01 at 11:21 +0530, Vinod Koul wrote: > > On Fri, Apr 28, 2017 at 04:37:46PM +0300, Eugeniy Paltsev wrote: > > > In the current implementation dma_get_slave_caps is used to check > > > state of descriptor_reuse option. But dma_get_slave_caps includes > > > check if the channel supports slave transactions. > > > So DMA_CTRL_REUSE flag can be set (even for MEM-TO-MEM tranfers) > > > only if channel supports slave transactions. > > > > > > Now we can use DMA_CTRL_REUSE flag for all channel types. > > > Also it allows to test reusing mechanism with simply mem-to-mem dma > > > test. > > > > We do not want to allow that actually. Slave is always treated as a > > special > > case, so resue was allowed. > > > > With memcpy the assumptions are different and clients can do reuse. > > Could you please clarify why don't we want to allow use DMA_CTRL_REUSE > for mem-to-mem transfers? > > Reusing of mem-to-mem (MEMCPY and DMA_SG) descriptors will work fine on > virt-dma based drivers. Precisely, the client does not know if you have a virt-dma or some other kind if implementation For them they see a channel and use it! > Anyway the current implementation behaviour is quite strange: > If channel supports *slave* transfers DMA_CTRL_REUSE can be set to > slave and *mem-to-mem* transfers. > > And, of course, we can pass DMA_CTRL_REUSE flag to device_prep_dma_sg > or device_prep_dma_memcpy directly without checks. Yeah thats bad, do send a patch to forbid that.. -- ~Vinod
