On Sat, Apr 11, 2015 at 09:40:32PM +0200, Robert Jarzmik wrote: > Document the new design of the pxa dma driver. > > Signed-off-by: Robert Jarzmik <robert.jarzmik@xxxxxxx> > --- > Documentation/dmaengine/pxa_dma.txt | 157 ++++++++++++++++++++++++++++++++++++ > 1 file changed, 157 insertions(+) > create mode 100644 Documentation/dmaengine/pxa_dma.txt > > diff --git a/Documentation/dmaengine/pxa_dma.txt b/Documentation/dmaengine/pxa_dma.txt > new file mode 100644 > index 0000000..63db9fe > --- /dev/null > +++ b/Documentation/dmaengine/pxa_dma.txt > @@ -0,0 +1,157 @@ > +PXA/MMP - DMA Slave controller > +============================== > + > +Constraints > +----------- > + a) Transfers hot queuing > + A driver submitting a transfer and issuing it should be granted the transfer > + is queued even on a running DMA channel. this is bit confusing, esp latter part.. do you mean "A driver submitting a transfer and issuing it should be granted the transfer queue even on a running DMA channel" ?? > + This implies that the queuing doesn't wait for the previous transfer end, > + and that the descriptor chaining is not only done in the irq/tasklet code > + triggered by the end of the transfer. how is it differenat than current dmaengine semantics where you say issue_pending() is invoked when current transfer finished? Here is you have to do descriptor chaining so bit it. > + > + b) All transfers having asked for confirmation should be signaled > + Any issued transfer with DMA_PREP_INTERRUPT should trigger a callback call. > + This implies that even if an irq/tasklet is triggered by end of tx1, but > + at the time of irq/dma tx2 is already finished, tx1->complete() and > + tx2->complete() should be called. > + > + c) Channel residue calculation > + A channel should be able to report how much advanced is a transfer. The in a ^^^^ > + granularity is still descriptor based. This is not pxa specfic > + > + d) Channel running state > + A driver should be able to query if a channel is running or not. For the > + multimedia case, such as video capture, if a transfer is submitted and then > + a check of the DMA channel reports a "stopped channel", the transfer should > + not be issued until the next "start of frame interrupt", hence the need to > + know if a channel is in running or stopped state. How do you query that? > + > + e) Bandwidth guarantee > + The PXA architecture has 4 levels of DMAs priorities : high, normal, low. > + The high prorities get twice as much bandwidth as the normal, which get twice > + as much as the low priorities. > + A driver should be able to request a priority, especially the real-time > + ones such as pxa_camera with (big) throughputs. and how..? > + > + f) Transfer reusability > + An issued and finished transfer should be "reusable". The choice of > + "DMA_CTRL_ACK" should be left to the client, not the dma driver. again how is this pxa specfic, if not documented we should move this to dmaengine documentation -- ~Vinod -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
