Re: [PATCH v2 00/19] Add support for the LAN966x PCI device using a DT overlay

On Mon, May 27, 2024 at 06:14:27PM +0200, Herve Codina wrote:

Hi,

This series adds support for the LAN966x chip when used as a PCI
device.

For reference, the LAN996x chip is a System-on-chip that integrates an
Ethernet switch and a number of other traditional hardware blocks such
as a GPIO controller, I2C controllers, SPI controllers, etc. The
LAN996x can be used in two different modes:

- With Linux running on its Linux built-in ARM cores.
  This mode is already supported by the upstream Linux kernel, with the
  LAN996x described as a standard ARM Device Tree in
  arch/arm/boot/dts/microchip/lan966x.dtsi. Thanks to this support,
  all hardware blocks in the LAN996x already have drivers in the
  upstream Linux kernel.

- As a PCI device, thanks to its built-in PCI endpoint controller.
  In this case, the LAN996x ARM cores are not used, but all peripherals
  of the LAN996x can be accessed by the PCI host using memory-mapped
  I/O through the PCI BARs.

This series aims at supporting this second use-case. As all peripherals
of the LAN996x already have drivers in the Linux kernel, our goal is to
re-use them as-is to support this second use-case.

Therefore, this patch series introduces a PCI driver that binds on the
LAN996x PCI VID/PID, and when probed, instantiates all devices that are
accessible through the PCI BAR. As the list and characteristics of such
devices are non-discoverable, this PCI driver loads a Device Tree
overlay that allows to teach the kernel about which devices are
available, and allows to probe the relevant drivers in kernel, re-using
all existing drivers with no change.

This patch series for now adds a Device Tree overlay that describes an
initial subset of the devices available over PCI in the LAN996x, and
follow-up patch series will add support for more once this initial
support has landed.

In order to add this PCI driver, a number of preparation changes are
needed:

 - Patches 1 to 5 allow the reset driver used for the LAN996x to be
   built as a module. Indeed, in the case where Linux runs on the ARM
   cores, it is common to have the reset driver built-in. However, when
   the LAN996x is used as a PCI device, it makes sense that all its
   drivers can be loaded as modules.

 - Patches 6 and 7 improve the MDIO controller driver to properly
   handle its reset signal.

 - Patches 8 to 12 introduce the internal interrupt controller used in
   the LAN996x. It is one of the few peripherals in the LAN996x that
   are only relevant when the LAN996x is used as a PCI device, which is
   why this interrupt controller did not have a driver so far.

 - Patches 13 to 16 make some small additions to the OF core and
   PCI/OF core to consider the PCI device as an interrupt controller.
   This topic was previously mentioned in [1] to avoid the need of
   phandle interrupt parents which are not available at some points.

 - Patches 17 and 18 introduce the LAN996x PCI driver itself, together
   with its DT bindings.

We believe all items from the above list can be merged separately, with
no build dependencies. We expect:

 - Patches 1 to 5 to be taken by reset maintainers

 - Patches 6 and 7 to be taken by network driver maintainers

 - Patches 8 to 12 to be taken by irqchip maintainers

 - Patch 13 to 17 to be taken by DT/PCI maintainers

I've applied patches 13-17.

Rob