Re: [PATCH 0/2] PCI/CXL: Recover CXL Downstream Ports from PM Init failure

[Fabio M. De Francesco]

On Tue, 2026-04-28 at 20:24 +0200, 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
> 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(-)

v2 of this series is under active development but its design has been heavily
reworked wrt v1. All comments that are still relevant to the new version have
been taken into consideration.

Thanks,

Fabio