Re: [PATCH v3 0/3] PCI: of: update endpoint ranges dynamically

[Alex Elder <elder@riscstar.com>]

On 9/24/26 5:24 PM, Alex Elder wrote:
> A PCI endpoint bus is a devicetree construct that allows a PCI
> endpoint (function) to have sub-devices defined that are accessible
> in an SoC via the PCI endpoint's BARs.  Such a bus is represented as
> a devicetree sub-node for a PCI function having the name "pci-ep-bus".
> There can be one or more pci-ep-bus nodes.
> 
> A PCI function with a pci-ep-bus devicetree node must also define
> "#address-cells", "#size-cells", and "ranges" properties, to specify
> how endpoint bus addresses are translated to the PCI parent bus.
> 
> An endpoint bus address has three cells; the first indicates which of
> the function's BARs the address is associated with, and the other two
> specify a 64-bit (2 cell) offset within the BAR's region.
> 
> BAR base addresses are determined dynamically by the PCI enumeration
> process, so generally it's not possible to include them in a static
> devicetree file.  When this addressing scheme was introduced, this
> was not a problem because the devicetree content was generated
> dynamically--after booting--based on the information (including BAR
> addresses) available following PCI enumeration.

The PCI endpoint bus model implements an addressing scheme that
allows sub-devices to specify addresses relative to the base of
an endpoint BAR.  This avoids needing to know the address assigned
to the BAR, which cannot be known until runtime.

For users (such as the LAN966x) that rely on dynamically-created
devicetree nodes for PCI endpoints, the generated ranges property
already incorporates the assigned addresses.

However if a PCI endpoint is defined in devicetree statically (as
in the case for the Toshiba TC9564), its ranges property must get 
updated at runtime to reflect the addresses assigned by the PCI 
enumeration process.

The TC9564 requires the functionality provided by this series
for it to be able to use the PCI endpoint bus model.

   ==> Would someone please consider and comment on this change?

It reuses the code that generates the ranges property for
dynamically-created devicetree nodes, to ensure that the
static and dynamic cases are consistent.

Thank you.

					-Alex

> It is possible (and in some cases, necessary) to define the devicetree
> nodes that represent PCI devices ahead of time, in a statically-defined
> devicetree file.  In order to support the PCI endpoint bus model in this
> case it is necessary to dynamically update the static devicetree so that
> the BAR base addresses assigned during enumeration are reflected in the
> endpoint's "ranges" property.
> 
> This series implements that dynamic update, leveraging the same code
> used to create the "ranges" property when PCI_DYNAMIC_OF_NODES is
> enabled.  The first patch makes an argument to of_pci_get_addr_flags()
> optional.  The second patch separates the code that dynamically builds
> the property value into a helper function, and the last arranges for a
> statically-defined devicetree node for a PCI endpoint to have its
> "ranges" property updated (if it includes a "pci-ep-bus" sub-node)..
> 
> 					-Alex
> 
> Note: this series is built upon these patches:
>    https://lore.kernel.org/lkml/20260924150222.1179235-5-elder@riscstar.com/
> 
> The entire series (based on v7.3-rc4 and including those prerequisites)
> is available here:
>    https://github.com/riscstar/linux/tree/outgoing/dynamic_ranges-v3
> 
> Between version 2 and version 3:
> - The ranges property for a PCI endpoint with an existing devicetree node
>    is only updated if its ranges property has an empty value (i.e., it is
>    "ranges;", or is not defined)
> 
> Version 2 is available here:
>    https://lore.kernel.org/lkml/20260910021919.3421449-1-elder@riscstar.com/
> 
> Between version 1 and version 2:
> - Included the first patch (which was previously posted in a different
>    series)
> - Modified the last patch so the ranges property is updated only for
>    PCI endpoints having at least one "pci-ep-bus" node
> - Rebased on v7.3-rc2 (and the prerequisite series)
> 
> Version 1 is available here:
>    https://lore.kernel.org/lkml/20260813220717.1394644-1-elder@riscstar.com/
> 
> 
> Alex Elder (3):
>    PCI: of: make a flags argument optional
>    PCI: of: introduce of_pci_build_prop_ranges()
>    PCI: of: introduce of_pci_update_endpoint_node_ranges()
> 
>   drivers/pci/of.c          |  94 +++++++++++++++++++++++---
>   drivers/pci/of_property.c | 137 +++++++++++++++++++++++++-------------
>   drivers/pci/pci.h         |   1 +
>   3 files changed, 178 insertions(+), 54 deletions(-)
> 
> 
> base-commit: 6ba8359b84d69a07d508693551ed3f661d838e9f