Re: [PATCH v4 1/4] PCI: dwc: ep: Add bus_addr_base for outbound window

Bjorn Helgaas
2024-10-25T22:31:04Z

On Thu, Oct 24, 2024 at 04:41:43PM -0400, Frank Li wrote:
> Endpoint Root complex
> ┌───────┐ ┌─────────┐
> ┌─────┐ │ EP │ │ │ ┌─────┐
> │ │ │ Ctrl │ │ │ │ CPU │
> │ DDR │ │ │ │ ┌────┐ │ └──┬──┘
> │ │◄──────┼─ATU ◄─┼────────┼─┤BarN│◄─┼─────────┘
> │ │ │ │ │ └────┘ │ Outbound Transfer
> └─────┘ │ │ │ │
> │ │ │ │
> │ │ │ │
> │ │ │ │ Inbound Transfer
> │ │ │ │ ┌──▼──┐
> ┌───────┐ │ │ │ ┌───────┼─────►│DDR │
> │ │ outbound Transfer* │ │ │ └─────┘
> ┌─────┐ │ Bus ┼─────►│ ATU ─┬────────┼─┘ │
> │ │ │ Fabric│Bus │ │ PCI Addr │
> │ CPU ├───►│ │Addr │ │ 0xA000_0000 │
> │ │CPU │ │0x8000_0000 │ │ │
> └─────┘Addr└───────┘ │ │ │ │
> 0x7000_0000 └───────┘ └─────────┘
>
> Add `bus_addr_base` to configure the outbound window address for CPU write.
> The bus fabric generally passes the same address to the PCIe EP controller,
> but some bus fabrics convert the address before sending it to the PCIe EP
> controller.
>
> Above diagram, CPU write data to outbound windows address 0x7000_0000,
> Bus fabric convert it to 0x8000_0000. ATU should use bus address
> 0x8000_0000 as input address and convert to PCI address 0xA000_0000.

Thanks for the diagram and description. I don't think the top half is
relevant to *this* patch, is it? I think this patch is only concerned
with the address translations between the CPU in the endpoint and the
PCI bus address. In this case it happens in two steps: the bus fabric
applies one offset, and the ATU applies a second offset.

Unless the top half is relevant, I would omit it and simply use
something like this:

Endpoint
┌───────────────────────────────────────────────┐
│ pcie-ep@5f010000 │
│ ┌────────────────┐│
│ │ Endpoint ││
│ │ PCIe ││
│ │ Controller ││
│ bus@5f000000 │ ││
│ ┌──────────┐ │ ││
│ │ │ Outbound Transfer ││
│┌─────┐ │ Bus ┼─────►│ ATU ──────────┬┬─────►
││ │ │ Fabric │Bus │ ││PCI Addr
││ CPU ├───►│ │Addr │ ││0xA000_0000
││ │CPU │ │0x8000_0000 ││
│└─────┘Addr└──────────┘ │ ││
│ 0x7000_0000 └────────────────┘│
└───────────────────────────────────────────────┘

If you don't want a big "Endpoint" box including the CPU and bus
fabric, that's OK with me, too. I added it because everything on the
PCI side only sees TLPs that contain PCI bus addresses, and can't tell
anything about the internal implementation of the Endpoint.

> Previously, `cpu_addr_fixup()` was used to handle address conversion. Now,
> the device tree provides this information, preferring a common method.
>
> bus@5f000000 {
> compatible = "simple-bus";
> ranges = <0x80000000 0x0 0x70000000 0x10000000>;
>
> pcie-ep@5f010000 {
> reg = <0x5f010000 0x00010000>,
> <0x80000000 0x10000000>;
> reg-names = "dbi", "addr_space";
> ...
> };
> ...
> };

I guess bus@5f000000 includes a "ranges" property because that
translation from 0x7000_0000 -> 0x8000_0000 is fixed or at least
not touched by Linux?

And the pcie-ep@5f010000 address translation from 0x8000_0000 to
0xA000_0000 *is* programmed by Linux and therefore can't be described
by a DT? But I guess Linux only programs the *PCI* side, and the
parent side (0x8000_0000) is fixed?

AFAICT, the "reg = <0x5f010000 0x00010000>" part is not relevant here.

I guess this implementation assumes there's only a single aperture
through the Bus Fabric, right?

And also a single ATU aperture through the endpoint PCIe controller?

And also that there's only one layer of Bus Fabric address
translation? The fact that only a few DWC controllers have this
translation suggests that this part of the picture might be external
to the DWC IP and there could be more variation. But I guess there's
no point in adding code for topologies that don't exist; we can deal
with that if the need ever arises.

> 'ranges' in bus@5f000000 descript how address convert from CPU address
> to bus address.
>
> Use `of_property_read_reg()` to obtain the bus address and set it to the
> ATU correctly, eliminating the need for vendor-specific cpu_addr_fixup().
>
> Add 'using_dtbus_info' to indicate device tree reflect correctly bus
> address translation in case break compatibility.
>
> Signed-off-by: Frank Li <Frank.Li@nxp.com>
> ---
> Change from v3 to v4
> - change bus_addr_base to u64 to fix 32bit build error
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202410230328.BTHareG1-lkp@intel.com/
>
> Change from v2 to v3
> - Add using_dtbus_info to control if use device tree bus ranges
> information.
> ---
> drivers/pci/controller/dwc/pcie-designware-ep.c | 14 +++++++++++++-
> drivers/pci/controller/dwc/pcie-designware.h | 9 +++++++++
> 2 files changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/controller/dwc/pcie-designware-ep.c b/drivers/pci/controller/dwc/pcie-designware-ep.c
> index 43ba5c6738df1..81b4057befa62 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-ep.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-ep.c
> @@ -9,6 +9,7 @@
> #include <linux/align.h>
> #include <linux/bitfield.h>
> #include <linux/of.h>
> +#include <linux/of_address.h>
> #include <linux/platform_device.h>
>
> #include "pcie-designware.h"
> @@ -294,7 +295,7 @@ static int dw_pcie_ep_map_addr(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
>
> atu.func_no = func_no;
> atu.type = PCIE_ATU_TYPE_MEM;
> - atu.cpu_addr = addr;
> + atu.cpu_addr = addr - ep->phys_base + ep->bus_addr_base;

Tangent: Maybe dw_pcie_ob_atu_cfg.cpu_addr isn't exactly the right
name, since it now contains an address that is not a CPU physical
address. Not a question for *this* patch though.

> atu.pci_addr = pci_addr;
> atu.size = size;
> ret = dw_pcie_ep_outbound_atu(ep, &atu);
> @@ -861,6 +862,7 @@ int dw_pcie_ep_init(struct dw_pcie_ep *ep)
> struct device *dev = pci->dev;
> struct platform_device *pdev = to_platform_device(dev);
> struct device_node *np = dev->of_node;
> + int index;
>
> INIT_LIST_HEAD(&ep->func_list);
>
> @@ -873,6 +875,16 @@ int dw_pcie_ep_init(struct dw_pcie_ep *ep)
> return -EINVAL;
>
> ep->phys_base = res->start;
> + ep->bus_addr_base = ep->phys_base;
> +
> + if (pci->using_dtbus_info) {
> + index = of_property_match_string(np, "reg-names", "addr_space");
> + if (index < 0)
> + return -EINVAL;
> +
> + of_property_read_reg(np, index, &ep->bus_addr_base, NULL);
> + }

If this translation were fixed, I suppose we'd extract something from
a "ranges" property that contains (child-bus-address,
parent-bus-address) information. So I suppose "addr_space" contains a
fixed parent-bus-address, and is setting the child (PCI) bus address,
right?

If so, I might add a comment here for other readers who come this way.
(And me, because I won't remember the next time I read it :)

> ep->addr_size = resource_size(res);
>
> if (ep->ops->pre_init)
> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> index 347ab74ac35aa..f10b533b04f77 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.h
> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> @@ -410,6 +410,7 @@ struct dw_pcie_ep {
> struct list_head func_list;
> const struct dw_pcie_ep_ops *ops;
> phys_addr_t phys_base;
> + u64 bus_addr_base;
> size_t addr_size;
> size_t page_size;
> u8 bar_to_atu[PCI_STD_NUM_BARS];
> @@ -463,6 +464,14 @@ struct dw_pcie {
> struct reset_control_bulk_data core_rsts[DW_PCIE_NUM_CORE_RSTS];
> struct gpio_desc *pe_rst;
> bool suspended;
> + /*
> + * Use device tree 'ranges' property of bus node instead using
> + * cpu_addr_fixup(). Some old platform dts 'ranges' in bus node may not
> + * reflect real hardware's behavior. In case break these platform back
> + * compatibility, add below flags. Set it true if dts already correct
> + * indicate bus fabric address convert.
> + */
> + bool using_dtbus_info;
> };
>
> #define to_dw_pcie_from_pp(port) container_of((port), struct dw_pcie, pp)
>
> --
> 2.34.1
>