Re: [PATCH v2 0/3] PCI: of: update endpoint ranges dynamically

[Alex Elder <elder@riscstar.com>]

On 9/9/26 9:19 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.

Does anyone have any questions about this?

The devicetree pci-ep-bus mechanism defines one or more buses
under a PCI endpoint function node (either one per BAR, or one
node representing more than one BAR).  Being a bus, it depends on
ranges properties to translate between the local (BAR) address
space and the parent (PCI) address space.

If a devicetree node is predefined (as is the case for the Toshiba
TC9564 SoC), it cannot correctly define an endpoint's ranges
property, because the PCI address space is determined dynamically
during the PCI enumeration process.

This series addresses that by replacing the PCI function's
devicetree ranges property at runtime, to reflect each BAR's
assigned addresses.

There exist other users of the pci-ep-bus, and in particular
the LAN966x driver generates an entire devicetree node to
represent the PCI endpoint function--including dynamically
generating this ranges property.

This series intentionally reuses the code that generates
the ranges property for the "fully dynamic" case used for
LAN966x.

This series (or another doing something comparable) is
required for the TC9564 SoC to function using pci-ep-bus.

					-Alex


> 
> 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.
> 
> 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/20260908213459.2519059-1-elder@riscstar.com/
> 
> The entire series (based on v7.3-rc2 and including those prerequisites)
> is available here:
>    https://github.com/riscstar/linux/tree/outgoing/dynamic_ranges-v2
> 
> 
> 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          |  89 ++++++++++++++++++++++---
>   drivers/pci/of_property.c | 137 +++++++++++++++++++++++++-------------
>   drivers/pci/pci.h         |   1 +
>   3 files changed, 173 insertions(+), 54 deletions(-)
> 
> 
> base-commit: 857c3561ea9f2c3107b5c6d830d3b3face159cbc