Hi, On 31/05/19 1:19 PM, Arnd Bergmann wrote: > On Fri, May 31, 2019 at 8:32 AM Vinod Koul <vk...@kernel.org> wrote: >> On 31-05-19, 10:50, Kishon Vijay Abraham I wrote: >>> On 31/05/19 10:37 AM, Vinod Koul wrote: >>>> On 30-05-19, 11:16, Kishon Vijay Abraham I wrote: >>>>> >>>>> right, my initial thought process was to use only dmaengine APIs in >>>>> pci-epf-test so that the system DMA or DMA within the PCIe controller can >>>>> be >>>>> used transparently. But can we register DMA within the PCIe controller to >>>>> the >>>>> DMA subsystem? AFAIK only system DMA should register with the DMA >>>>> subsystem. >>>>> (ADMA in SDHCI doesn't use dmaengine). Vinod Koul can confirm. >>>> >>>> So would this DMA be dedicated for PCI and all PCI devices on the bus? >>> >>> Yes, this DMA will be used only by PCI ($patch is w.r.t PCIe device mode. So >>> all endpoint functions both physical and virtual functions will use the DMA >>> in >>> the controller). >>>> If so I do not see a reason why this cannot be using dmaengine. The use >>> >>> Thanks for clarifying. I was under the impression any DMA within a >>> peripheral >>> controller shouldn't use DMAengine. >> >> That is indeed a correct assumption. The dmaengine helps in cases where >> we have a dma controller with multiple users, for a single user case it >> might be overhead to setup dma driver and then use it thru framework. >> >> Someone needs to see the benefit and cost of using the framework and >> decide. > > I think the main question is about how generalized we want this to be. > There are lots of difference PCIe endpoint implementations, and in > case of some licensable IP cores like the designware PCIe there are > many variants, as each SoC will do the implementation in a slightly > different way. > > If we can have a single endpoint driver than can either have an > integrated DMA engine or use an external one, then abstracting that > DMA engine helps make the driver work more readily either way. > > Similarly, there may be PCIe endpoint implementations that have > a dedicated DMA engine in them that is not usable for anything else, > but that is closely related to an IP core we already have a dmaengine > driver for. In this case, we can avoid duplication.
right. Either way it makes more sense to register DMA embedded within the PCIe endpoint controller instead of creating epc_ops for DMA transfers. Thanks Kishon
