On Thu, Mar 3, 2022 at 11:48 AM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > On Wed, Mar 02, 2022 at 03:28:48PM -0600, Zhi Li wrote: > > On Wed, Mar 2, 2022 at 3:21 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > > On Wed, Mar 02, 2022 at 02:49:45PM -0600, Zhi Li wrote: > > > > On Wed, Mar 2, 2022 at 2:15 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > > > > On Tue, Mar 01, 2022 at 09:26:45PM -0600, Frank Li wrote: > > > > > > ... > > > > > > > The DMA can transfer data to any remote address location > > > > > > regardless PCI address space size. > > > > > > > > > > What is this sentence telling us? Is it merely that the DMA "inbound > > > > > address space" may be larger than the MMIO "outbound address space"? > > > > > I think there's no necessary connection between them, and there's no > > > > > need to call it out as though it's something special. > > > > > > > > There are outbound address windows. such as 256M, but RC sides have more > > > > than 256M ddr memory, such as 16GB. If CPU or external DMA controller, > > > > only can access 256M > > > > address space. > > > > > > > > But if using an embedded DMA controller, it can access the whole RC's > > > > 16G address without > > > > changing iAtu mapping. > > > > > > > > I want to say why I need enable embedded DMA for EP. > > > > > > OK, so if IIUC, the DMA controller is embedded in the imx6 host bridge > > > (of course; that's obvious from what you're doing here). And unlike > > > DMA from devices *below* the host bridge, DMAs from the embedded > > > controller don't go through the iATU, so they are not subject to any > > > of the iATU limitations. Right? > > > > Yes! > > I guess that means the DMA controller is functionally and logically > sort of a separate device from the PCI host bridge? Sounds like the > DMA controller doesn't receive or generate PCI transactions? It is not a separated DMA controller physically. LOCAL BUS -> [ DMA, PCI controller (EP/RC) ]. -> PCI Bus. DMA Read data from local bus, then convert to PCI TLP transaction sent out to PCI bus. It is mainly used for EP mode. It also works for RC mode, but not commonly. > > Bjorn
