Re: [PATCH v10 1/3] PCI: microchip: Fix outbound address translation tables

Bjorn Helgaas
2025-01-15T00:13:10Z

On Fri, Oct 11, 2024 at 03:00:41PM +0100, daire.mcnamara@microchip.com wrote:
> From: Daire McNamara <daire.mcnamara@microchip.com>
>
> On Microchip PolarFire SoC (MPFS) the PCIe Root Port can be behind one of
> three general-purpose Fabric Interface Controller (FIC) buses that
> encapsulate an AXI-M interface. That FIC is responsible for managing
> the translations of the upper 32-bits of the AXI-M address. On MPFS,
> the Root Port driver needs to take account of that outbound address
> translation done by the parent FIC bus before setting up its own
> outbound address translation tables. In all cases on MPFS,
> the remaining outbound address translation tables are 32-bit only.
>
> Limit the outbound address translation tables to 32-bit only.

I don't quite understand what this is saying. It seems like the code
keeps only the low 32 bits of a PCI address and throws away any
address bits above the low 32.

If that's what the FIC does, I wouldn't describe the FIC as
"translating the upper 32 bits" since it sounds like the translation
is just truncation.

I guess it must be more complicated than that? I assume you can still
reach BARs that have PCI addresses above 4GB using CPU loads/stores?

The apertures through the host bridge for MMIO access are described by
DT ranges properties, so this must be something that can't be
described that way?

> Fixes: 6f15a9c9f941 ("PCI: microchip: Add Microchip Polarfire PCIe controller driver")
> Signed-off-by: Daire McNamara <daire.mcnamara@microchip.com>
> Acked-by: Conor Dooley <conor.dooley@microchip.com>
> Reviewed-by: Ilpo Jarvinen <ilpo.jarvinen@linux.intel.com>
> ---
> .../pci/controller/plda/pcie-microchip-host.c | 30 ++++++++++++++++---
> 1 file changed, 26 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/pci/controller/plda/pcie-microchip-host.c b/drivers/pci/controller/plda/pcie-microchip-host.c
> index 48f60a04b740..fa4c85be21f0 100644
> --- a/drivers/pci/controller/plda/pcie-microchip-host.c
> +++ b/drivers/pci/controller/plda/pcie-microchip-host.c
> @@ -21,6 +21,8 @@
> #include "../../pci.h"
> #include "pcie-plda.h"
>
> +#define MC_OUTBOUND_TRANS_TBL_MASK GENMASK(31, 0)
> +
> /* PCIe Bridge Phy and Controller Phy offsets */
> #define MC_PCIE1_BRIDGE_ADDR 0x00008000u
> #define MC_PCIE1_CTRL_ADDR 0x0000a000u
> @@ -612,6 +614,27 @@ static void mc_disable_interrupts(struct mc_pcie *port)
> writel_relaxed(GENMASK(31, 0), bridge_base_addr + ISTATUS_HOST);
> }
>
> +static int mc_pcie_setup_iomems(struct pci_host_bridge *bridge,
> + struct plda_pcie_rp *port)
> +{
> + void __iomem *bridge_base_addr = port->bridge_addr;
> + struct resource_entry *entry;
> + u64 pci_addr;
> + u32 index = 1;
> +
> + resource_list_for_each_entry(entry, &bridge->windows) {
> + if (resource_type(entry->res) == IORESOURCE_MEM) {
> + pci_addr = entry->res->start - entry->offset;
> + plda_pcie_setup_window(bridge_base_addr, index,
> + entry->res->start & MC_OUTBOUND_TRANS_TBL_MASK,
> + pci_addr, resource_size(entry->res));
> + index++;
> + }
> + }
> +
> + return 0;
> +}
> +
> static int mc_platform_init(struct pci_config_window *cfg)
> {
> struct device *dev = cfg->parent;
> @@ -622,15 +645,14 @@ static int mc_platform_init(struct pci_config_window *cfg)
> int ret;
>
> /* Configure address translation table 0 for PCIe config space */
> - plda_pcie_setup_window(bridge_base_addr, 0, cfg->res.start,
> - cfg->res.start,
> - resource_size(&cfg->res));
> + plda_pcie_setup_window(bridge_base_addr, 0, cfg->res.start & MC_OUTBOUND_TRANS_TBL_MASK,
> + 0, resource_size(&cfg->res));
>
> /* Need some fixups in config space */
> mc_pcie_enable_msi(port, cfg->win);
>
> /* Configure non-config space outbound ranges */
> - ret = plda_pcie_setup_iomems(bridge, &port->plda);
> + ret = mc_pcie_setup_iomems(bridge, &port->plda);
> if (ret)
> return ret;
>
> --
> 2.43.0
>