Hi Vinod, On 31/05/19 12:02 PM, Vinod Koul wrote: > On 31-05-19, 10:50, Kishon Vijay Abraham I wrote: >> Hi Vinod, >> >> On 31/05/19 10:37 AM, Vinod Koul wrote: >>> Hi Kishon, >>> >>> On 30-05-19, 11:16, Kishon Vijay Abraham I wrote: >>>> +Vinod Koul >>>> >>>> Hi, >>>> >>>> On 30/05/19 4:07 AM, Alan Mikhak wrote: >>>>> On Mon, May 27, 2019 at 2:09 AM Gustavo Pimentel >>>>> <Gustavo.Pimentel@xxxxxxxxxxxx> wrote: >>>>>> >>>>>> On Fri, May 24, 2019 at 20:42:43, Alan Mikhak <alan.mikhak@xxxxxxxxxx> >>>>>> wrote: >>>>>> >>>>>> Hi Alan, >>>>>> >>>>>>> On Fri, May 24, 2019 at 1:59 AM Gustavo Pimentel >>>>>>> <Gustavo.Pimentel@xxxxxxxxxxxx> wrote: >>>>>>>> >>>>>>>> Hi Alan, >>>>>>>> >>>>>>>> This patch implementation is very HW implementation dependent and >>>>>>>> requires the DMA to exposed through PCIe BARs, which aren't always the >>>>>>>> case. Besides, you are defining some control bits on >>>>>>>> include/linux/pci-epc.h that may not have any meaning to other types of >>>>>>>> DMA. >>>>>>>> >>>>>>>> I don't think this was what Kishon had in mind when he developed the >>>>>>>> pcitest, but let see what Kishon was to say about it. >>>>>>>> >>>>>>>> I've developed a DMA driver for DWC PCI using Linux Kernel DMAengine API >>>>>>>> and which I submitted some days ago. >>>>>>>> By having a DMA driver which implemented using DMAengine API, means the >>>>>>>> pcitest can use the DMAengine client API, which will be completely >>>>>>>> generic to any other DMA implementation. >>>> >>>> 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. The DMA within the endpoint controller can indeed be used by multiple users for e.g in the case of multi function EP devices or SR-IOV devices, all the function drivers can use the DMA in the endpoint controller. I think it makes sense to use dmaengine for DMA within the endpoint controller. > >>> case would be memcpy for DMA right or mem to device (vice versa) transfers? >> >> The device is memory mapped so it would be only memcopy. >>> >>> Btw many driver in sdhci do use dmaengine APIs and yes we are missing >>> support in framework than individual drivers >> >> I think dmaengine APIs is used only when the platform uses system DMA and not >> ADMA within the SDHCI controller. IOW there is no dma_async_device_register() >> to register ADMA in SDHCI with DMA subsystem. > > We are looking it from the different point of view. You are looking for > dmaengine drivers in that (which would be in drivers/dma/) and I am > pointing to users of dmaengine in that. > > So the users in mmc would be ones using dmaengine APIs: > $git grep -l dmaengine_prep_* drivers/mmc/ > > which tells me 17 drivers! right. For the endpoint case, drivers/pci/controller should register with the dmaengine i.e if the controller has aN embedded DMA (I think it should be okay to keep that in drivers/pci/controller itself instead of drivers/dma) and drivers/pci/endpoint/functions/ should use dmaengine API's (Depending on the platform, this will either use system DMA or DMA within the PCI controller). Thanks Kishon
