Re: [PATCH v5] PCI: s390: Expose the UID as an arch specific PCI slot attribute

[Randy Dunlap]

On 4/1/26 7:50 AM, Niklas Schnelle wrote:
> On s390, an individual PCI function can generally be identified by two
> identifiers, the FID and the UID. Which identifier is used depends on
> the scope and the platform configuration.
> 
> The first identifier, the FID, is always available and identifies a PCI
> device uniquely within a machine. The FID may be virtualized by
> hypervisors, but on the LPAR level, the machine scope makes it
> impossible to create the same configuration based on FIDs on two
> different LPARs of the same machine, and difficult to reuse across
> machines.
> 
> Such matching LPAR configurations are useful, though, allowing
> standardized setups and booting a Linux installation on different LPARs.
> To this end the UID, or user-defined identifier, was introduced. While
> it is only guaranteed to be unique within an LPAR and only if indicated
> by firmware, it allows users to replicate PCI device setups.
> 
> On s390, which uses a machine hypervisor, a per PCI function hotplug
> model is used. The shortcoming with the UID then is, that it is not
> visible to the user without first attaching the PCI function and
> accessing the "uid" device attribute. The FID, on the other hand, is
> used as the slot name and is thus known even with the PCI function in
> standby.
> 
> Remedy this shortcoming by providing the UID as an attribute on the slot
> allowing the user to identify a PCI function based on the UID without
> having to first attach it. Do this via a macro mechanism analogous to
> what was introduced by commit 265baca69a07 ("s390/pci: Stop usurping
> pdev->dev.groups") for the PCI device attributes.
> 
> Reviewed-by: Gerd Bayer <gbayer@xxxxxxxxxxxxx>
> Reviewed-by: Julian Ruess <julianr@xxxxxxxxxxxxx>
> Signed-off-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
> ---
> Note: I considered adding the UID as a generic slot index attribute
> analogous to the PCI device index attribute (SMBIOS index / s390 UID)
> but decided against it as this seems rather s390 specific.
> 
> v4->v5:
> - Rebase on v7.0-rc6
> - Reworded note
> - Add documentation for the new attribute
> - Link to v4: https://lore.kernel.org/r/20251217-uid_slot-v4-1-559ceb59ba69@xxxxxxxxxxxxx
> 
> v3->v4:
> - Rebase on v6.19-rc1
> - Collect R-bs
> - Link to v3: https://lore.kernel.org/r/20251015-uid_slot-v3-1-44389895c1bb@xxxxxxxxxxxxx
> ---
> 
> ---
>  Documentation/arch/s390/pci.rst |  7 +++++++
>  arch/s390/include/asm/pci.h     |  4 ++++
>  arch/s390/pci/pci_sysfs.c       | 20 ++++++++++++++++++++
>  drivers/pci/slot.c              | 13 ++++++++++++-
>  4 files changed, 43 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/arch/s390/pci.rst b/Documentation/arch/s390/pci.rst
> index d5755484d8e75c7bf67a350e61bbe04f0452a2fa..03afb57ece4df90a75597cb34c1f048c2e162b67 100644
> --- a/Documentation/arch/s390/pci.rst
> +++ b/Documentation/arch/s390/pci.rst
> @@ -55,6 +55,13 @@ Entries specific to zPCI functions and entries that hold zPCI information.
>  
>    - /sys/bus/pci/slots/XXXXXXXX/power
>  
> +  In addition to using the FID as the name of the slot the slot directory
> +  also contains the following s390 specific slot attributes

                                 s390-specific

Use a period (full stop, '.') at the end of the sentence above.

> +
> +  - uid
> +    The User-defined identifier (UID) of the function which may be configured
> +    by this slot. See also the corresponding attribute of the device.

These 3 lines are run together in html output. Maybe add a ':' or '-' after
uid?

> +>    A physical function that currently supports a virtual function cannot be
>    powered off until all virtual functions are removed with:
>    echo 0 > /sys/bus/pci/devices/XXXX:XX:XX.X/sriov_numvf


-- 
~Randy