Vinod Koul <vinod.koul@xxxxxxxxx> writes: > On Sat, Apr 11, 2015 at 09:40:32PM +0200, Robert Jarzmik wrote: >> Document the new design of the pxa dma driver. >> + 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" ?? Euh no, I meant that a transfer which is submitted and issued on a _phy_ doesn't wait for a _phy_ to stop and restart, but is submitted on a "running channel". The other drivers, especially mmp_pdma waited for the phy to stop before relaunching a new transfer. I don't have a clear idea on a better wording yet ... >> + 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. Your sentence is a bit difficult for me to understand. >> + c) Channel residue calculation >> + A channel should be able to report how much advanced is a transfer. The > in a ^^^^ For v3. >> + granularity is still descriptor based. > This is not pxa specfic True. Do you want me to remove the (c) from the document ? >> + >> + 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? With dma_async_is_tx_complete() giving : - dma_cookie_t last_submitted - dma_cookie_t last_issued The channel is still running if (last_submitted < last_issued). > >> + >> + 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..? By passing this information : - in a devicetree environment, check pxad_dma_xlate() - in a platform device environment, check pxad_filter_fn() >> + 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 Yes, I agree. I should move this to dmaengine slave documentation, in Documentation/dmaengine/provider.txt (in the Misc notes section). Do you want me to submit a patch to change the "Undocumented feature" into a properly documented feature ? Cheers. -- Robert -- 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
