Re: [PATCH 05/15] cxl/acpi: Add probe function to detect restricted CXL hosts in RCD mode

[Bjorn Helgaas]

On Wed, Aug 31, 2022 at 10:15:53AM +0200, Robert Richter wrote:
> Restricted CXL device (RCD) mode (formerly CXL 1.1) uses a different
> enumeration scheme other than CXL VH (formerly CXL 2.0). In RCD mode a
> host/device (RCH-RCD) pair shows up as a legal PCIe hierarchy with an
> ACPI host bridge ("PNP0A08" or "ACPI0016" HID) and RCiEP connected to
> it with a description of the CXL device.
> 
> Add function cxl_restricted_host_probe() to probe RCD enumerated
> devices. The function implements a loop that detects all CXL capable
> ACPI PCI root bridges in the system (RCD mode only). The iterator
> function cxl_find_next_rch() is introduced to walk through all of the
> CXL hosts. The loop will then enable all CXL devices connected to the
> host. For now, only implement an empty loop with an iterator that
> returns all pci host bridges in the system.
> 
> The probe function is triggered by adding an own root device for RCHs.
> This is different to CXL VH where an ACPI "ACPI0017" root device
> exists. Its detection starts the CXL host detection. In RCD mode such
> a device does not necessarily exists, so solve this by creating a
> plain platform device that is not an ACPI device and is root only for
> RCHs.

Drive-by nitpicks: 
s/PCI root bridges/PCI host bridges/ to match other uses
s/pci host bridges/PCI host bridges/ to match other "PCI" uses
s/does not necessarily exists/does not necessarily exist/