| Message ID | 20170428133746.1855-1-Eugeniy.Paltsev@synopsys.com (mailing list archive) |
|---|---|
| State | Rejected |
| Headers | show |
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. > > Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com> > --- > include/linux/dmaengine.h | 6 +----- > 1 file changed, 1 insertion(+), 5 deletions(-) > > diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h > index 5336808..92cf8b0 100644 > --- a/include/linux/dmaengine.h > +++ b/include/linux/dmaengine.h > @@ -1376,11 +1376,7 @@ static inline int dma_get_slave_caps(struct dma_chan *chan, > > static inline int dmaengine_desc_set_reuse(struct dma_async_tx_descriptor *tx) > { > - struct dma_slave_caps caps; > - > - dma_get_slave_caps(tx->chan, &caps); > - > - if (caps.descriptor_reuse) { > + if (tx->chan->device->descriptor_reuse) { > tx->flags |= DMA_CTRL_REUSE; > return 0; > } else { > -- > 2.9.3 > > -- > To unsubscribe from this list: send the line "unsubscribe dmaengine" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
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. 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. > > > > Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com> > > --- > > include/linux/dmaengine.h | 6 +----- > > 1 file changed, 1 insertion(+), 5 deletions(-) > > > > diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h > > index 5336808..92cf8b0 100644 > > --- a/include/linux/dmaengine.h > > +++ b/include/linux/dmaengine.h > > @@ -1376,11 +1376,7 @@ static inline int dma_get_slave_caps(struct > > dma_chan *chan, > > > > static inline int dmaengine_desc_set_reuse(struct > > dma_async_tx_descriptor *tx) > > { > > - struct dma_slave_caps caps; > > - > > - dma_get_slave_caps(tx->chan, &caps); > > - > > - if (caps.descriptor_reuse) { > > + if (tx->chan->device->descriptor_reuse) { > > tx->flags |= DMA_CTRL_REUSE; > > return 0; > > } else { > > -- > > 2.9.3 > > > > -- -- Eugeniy Paltsev
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..
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h index 5336808..92cf8b0 100644 --- a/include/linux/dmaengine.h +++ b/include/linux/dmaengine.h @@ -1376,11 +1376,7 @@ static inline int dma_get_slave_caps(struct dma_chan *chan, static inline int dmaengine_desc_set_reuse(struct dma_async_tx_descriptor *tx) { - struct dma_slave_caps caps; - - dma_get_slave_caps(tx->chan, &caps); - - if (caps.descriptor_reuse) { + if (tx->chan->device->descriptor_reuse) { tx->flags |= DMA_CTRL_REUSE; return 0; } else {
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. Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com> --- include/linux/dmaengine.h | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-)