Re:

[Dave Jiang]

On 4/28/26 11:24 AM, Fabio M. De Francesco wrote:
> Subject: [PATCH 0/2] PCI/CXL: Recover CXL Downstream Ports from PM Init failure
> 
> CXL r4.0 sec 8.1.5.1 Implementation Note describes a scenario in which a
> Secondary Bus Reset, a Link Down, or Downstream Port Containment on a

I'm not sure if this series covers a Link Down event (i.e. hotplug). As I recall, cxl_reset_bus_function() only happens via sysfs trigger.

DJ


> CXL Downstream Port prevents Port PM Init from completing when ACS
> Source Validation is enabled on the Downstream Port. The spec states
> that another SBR alone does not recover the port and describes a
> software recovery sequence.  
> 
> Patch 1 extends cxl_reset_bus_function(), the helper backing the cxl_bus
> PCI/CXL reset method exposed to userspace via sysfs. It saves, clears,
> and restores ACS Source Validation and Bus Master Enable on the CXL
> Downstream Port around the SBR it issues. This keeps the userspace
> cxl_bus reset path from leaving the port unable to complete PM Init.
> 
> Patch 2 adds a recovery pass during CXL enumeration. For each CXL
> Downstream Port in a memdev's ancestry, the CXL core checks whether PM
> Init has completed. If it has not, regardless of what caused the
> failure, it invokes cxl_reset_bus_function() on the child below the port
> in the hope of restoring the port to a usable state. CXL enumeration
> re-runs after events that tear down and re-probe the memdev, including
> DPC, AER, and Link Down, so those paths reach this recovery.
> 
> This small series is developed from an old RFC v3:
> https://lore.kernel.org/linux-cxl/20260330193347.25072-1-fabio.m.de.francesco@xxxxxxxxxxxxxxx/
> 
> Fabio M. De Francesco (2):
>   PCI/CXL: Allow PM Init to complete on cxl_bus reset if ACS SV enabled
>   cxl/core: Recover from PM Init failure via cxl_reset_bus_function()
> 
> drivers/cxl/core/pci.c        | 30 ++++++++++++++++++++
>  drivers/cxl/core/port.c       | 22 +++++++++++++++
>  drivers/cxl/cxlpci.h          |  3 ++
>  drivers/pci/pci.c             | 52 ++++++++++++++++++++++++++++++++++-
>  include/linux/pci.h           |  1 + 
>  include/uapi/linux/pci_regs.h |  2 ++
>  6 files changed, 109 insertions(+), 1 deletion(-)
>