PCI/DOE: Expose DOE features via sysfs

PCIe r6.0 added support for Data Object Exchange (DOE).  When DOE is
supported, the DOE Discovery Feature must be implemented per PCIe r6.1, sec
6.30.1.1. DOE allows a requester to obtain information about the other DOE
features supported by the device.

The kernel already queries the DOE features supported and caches the
values.  Expose the values in sysfs to allow user space to determine which
DOE features are supported by the PCIe device.

By exposing the information to userspace, tools like lspci can relay the
information to users. By listing all of the supported features we can allow
userspace to parse the list, which might include vendor specific features
as well as yet to be supported features.

As the DOE Discovery feature must always be supported we treat it as a
special named attribute case. This allows the usual PCI attribute_group
handling to correctly create the doe_features directory when registering
pci_doe_sysfs_group (otherwise it doesn't and sysfs_add_file_to_group()
will seg fault).

After this patch is supported you can see something like this when
attaching a DOE device:

  $ ls /sys/devices/pci0000:00/0000:00:02.0//doe*
  0001:01        0001:02        doe_discovery

Link: https://lore.kernel.org/r/20250306075211.1855177-3-alistair@alistair23.me
Signed-off-by: Alistair Francis <alistair@alistair23.me>
[bhelgaas: drop pci_doe_sysfs_init() stub return, make
DEVICE_ATTR_RO(doe_discovery) static]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

0 files changed, 0 insertions, 0 deletions