Re: [PATCH v9 2/7] PCI: dwc: Rename cpu_addr to parent_bus_addr for ATU configuration

Frank Li
2025-02-13T16:03:04Z

On Thu, Jan 30, 2025 at 11:02:06AM -0500, Frank Li wrote:
> On Wed, Jan 29, 2025 at 05:23:50PM -0600, Bjorn Helgaas wrote:
> > On Tue, Jan 28, 2025 at 05:07:35PM -0500, Frank Li wrote:
> > > Rename `cpu_addr` to `parent_bus_addr` in the DesignWare ATU configuration.
> > > The ATU translates parent bus addresses to PCI addresses, which are often
> > > the same as CPU addresses but can differ in systems where the bus fabric
> > > translates addresses before passing them to the PCIe controller. This
> > > renaming clarifies the purpose and avoids confusion.
> >
> > Based on dw_pcie_ep_inbound_atu() below, I guess the ATU can also
> > translate PCI addresses from incoming DMA to parent bus addresses?
>
> Yes, but root complex don't use it. Only EP use it. because most PCI root
> complex system doesn't transfer incoming address, which generally use iommu
> to do that. Linux already allow a simple map by use dt's dma-ranges and dma
> API already handle it.
>
> previous 'cpu_addr' is actually 'dma_bus_addr'.
>
> >
> > It's worth noting here that this patch only renames the member, and
> > IIUC, parent_bus_addr still incorrectly contains CPU physical
> > addresses.
>
> Anyway, call 'cpu_addr' for dw_pcie_ep_inbound_atu is wrong. Only one place
> call dw_pcie_ep_inbound_atu(), that's dw_pcie_ep_set_bar(), which use
> epf_bar->phys_addr, I think name 'phys_addr' is okay because most case it
> is refer to dma address space.

Bjoin:
Do you any concern/comments about my reply? how to move forward?
keep old cpu_addr or rename to parent_bus_addr, or futher work need be done.

Frank

>
> Frank
> >
> > > +++ b/drivers/pci/controller/dwc/pcie-designware-ep.c
> > > @@ -128,7 +128,7 @@ static int dw_pcie_ep_write_header(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
> > > }
> > >
> > > static int dw_pcie_ep_inbound_atu(struct dw_pcie_ep *ep, u8 func_no, int type,
> > > - dma_addr_t cpu_addr, enum pci_barno bar,
> > > + dma_addr_t parent_bus_addr, enum pci_barno bar,
> > > size_t size)