Re: [PATCH v3 0/9] cxl: Delay HB port and switch dport probing until endpoint dev probe

[Robert Richter <rrichter@amd.com>]

On 03.06.25 06:55:15, Dave Jiang wrote:
> On 5/30/25 6:51 AM, Robert Richter wrote:

> > The port_num can no longer retrieved using sysfs. Previously, the X in
> > dportX could be used to identify the port number (former port_id)
> > which was identical to the numbers in the sysfs target_list entries.
> > This is esp. useful to reconstruct the decoder tree and map pci child
> > devices and its decoders to a parent decoder including its positions
> > in the target list. Maybe create a targetX symlink from the decoder
> > device to the child decoders of it?
> 

> The numbers in the target_list are dport->id and should reflect the
> dportX. Is this not what you are seeing?

Exactly, but I would prefer real numbers for the target list, that is,
uid and port_num.

> > 
> > Due to the different initialization order there is an odd port
> > numbering now showing up with unexpected, out-of-order sequence
> > numbers, e.g.:
> > 
> > /sys/bus/cxl/devices/port1/endpoint2
> > /sys/bus/cxl/devices/port1/endpoint3
> > /sys/bus/cxl/devices/port1/endpoint6
> > /sys/bus/cxl/devices/port4/endpoint5
> > /sys/bus/cxl/devices/port4/endpoint7
> > /sys/bus/cxl/devices/port4/endpoint10
> > /sys/bus/cxl/devices/port4/endpoint11
> > /sys/bus/cxl/devices/port8/endpoint9
> > /sys/bus/cxl/devices/port12/endpoint13
> > /sys/bus/cxl/devices/port12/endpoint14
> > 
> > Still, this is correct, but maybe we could force a specific order
> > during initialization, such as per-port initialization which should
> > result in a defined order? Note the shared numbering of ports and
> > endpoints is also confusing, maybe that could be changed here too?
> 

> I think the upstream expectation WRT sysfs device number enumeration
> (for all Linux kernel devices) is that no ordering should be
> expected as the devices are initialized async. And previous ordering
> appearance is merely coincidence and not the expectation. And the
> expectation for user tools is that they should not depend on device
> numbering order and identify the devices by other stable means.

sysfs still is human readable and for good reasons not some binary
blob you need a viewer for. Avoiding un-ordered enumeration where
possible helps understanding the topology. So let's think about it and
if possible find a way to get a defined numbering.

Thanks,

-Robert