Re: [PATCH v5 0/7] CXL: Add cxl_reset sysfs attribute for PCI devices

[Dave Jiang]

On 3/9/26 3:37 PM, Dave Jiang wrote:
> 
> 
> On 3/6/26 2:23 AM, smadhavan@xxxxxxxxxx wrote:
>> From: Srirangan Madhavan <smadhavan@xxxxxxxxxx>
>>
>> Hi folks!
>>
>> This patch series introduces support for the CXL Reset method for CXL
>> Type 2 devices, implementing the reset procedure outlined in CXL Spec [1]
>> v3.2, Sections 8.1.3, 9.6 and 9.7.
>>
>> v5 changes (from v4):
>> - Rebased on v7.0-rc1 and applied fixes from the review v4.
>> - Added CXL DVSEC and HDM save/restore as a prerequisite series [2]
>> - Switched from PCI reset method to sysfs
>>   interface at /sys/bus/pci/devices/.../cxl_reset (Dan, Alex)
>> - Removed all PCI core changes - reset logic stays in CXL driver
>> - Use cpu_cache_invalidate_memregion() instead of arch-specific code
>> - Removed CONFIG_X86/CONFIG_ARM64 ifdefs
>> - Added ABI documentation for sysfs interface
>>
>> v4 changes:
>> - Fix CXL reset capability check parentheses warning
>> - Gate CXL reset path on CONFIG_CXL_PCI reachability
>>
>> v3 changes:
>> - Restrict CXL reset to Type 2 devices only
>> - Add host and device cache flushing for sibling functions and region peers
>> - Add region teardown and memory online detection before reset
>> - Add configuration state save/restore (DVSEC, HDM, IDE)
>> - Split the series by subsystem and functional blocks
>>
>> Motivation:
>> -----------
>> - As support for Type 2 devices [6] is being introduced, more devices will
>>   require finer-grained reset mechanisms beyond bus-wide reset methods.
>>
>> - FLR does not affect CXL.cache or CXL.mem protocols, making CXL Reset
>>   the preferred method in some cases.
>>
>> - The CXL spec (Sections 7.2.3 Binding and Unbinding, 9.5 FLR) highlights use
>>   cases like function rebinding and error recovery, where CXL Reset is
>>   explicitly mentioned.
>>
>> ABI Change reasoning (v5):
>> -------------------------
>> Previous versions (v1-v4) integrated CXL reset as a new PCI reset method
>> in pci_reset_methods[]. Based on feedback from Dan Williams and Alex
>> Williamson, v5 switches to a sysfs-based approach.
>>
>> The key reasoning is that CXL Reset has expanded scope than existing PCI
>> reset methods. Mixing these in the same reset infrastructure causes
>> problems. Therefore selectively exposing a cxl_reset method in pci-sysfs
>> and leaving the existing interface unaffected.
>>
>> Change Description:
>> -------------------
>>
>> Patch 1: PCI: Add CXL DVSEC reset and capability register definitions
>> - Add reset and cache control bit definitions to pci_regs.h
>>
>> Patch 2: PCI: Export pci_dev_save_and_disable() and pci_dev_restore()
>> - Export for sibling function save/restore during CXL reset
>>
>> Patch 3: cxl: Add memory offlining and cache flush helpers
>> - Offline CXL memory regions before reset
>> - Flush CPU caches using cpu_cache_invalidate_memregion()
>>
>> Patch 4: cxl: Add multi-function sibling coordination for CXL reset
>> - Identify CXL.cachemem sibling functions via Non-CXL Function Map DVSEC
>> - Save/disable and restore sibling PCI functions around reset
>>
>> Patch 5: cxl: Add CXL DVSEC reset sequence and flow orchestration
>> - Implement cxl_dev_reset() to trigger reset via DVSEC
>> - Poll for reset completion with timeout
>> - cxl_do_reset() orchestrates the complete reset sequence with
>>   proper locking and error handling
>>
>> Patch 6: cxl: Add cxl_reset sysfs interface for PCI devices
>> - Expose /sys/bus/pci/devices/.../cxl_reset
>> - Only visible for devices with Reset Capable bit set
>> - Write "1" to trigger reset
>>
>> Patch 7: Documentation: ABI: Add CXL PCI cxl_reset sysfs attribute
>> - Document the new sysfs interface
>> - Explain scope, visibility, and error conditions
>>
>> Dependencies:
>> -------------
>>
>> This series depends on:
>>   [PATCH 0/5] PCI/CXL: Save and restore CXL DVSEC and HDM state across resets
>>   https://lore.kernel.org/linux-cxl/20260306080026.116789-1-smadhavan@xxxxxxxxxx/T/#t
>>
>> The cpu_cache_invalidate_memregion() call used for CPU cache flush currently
>> has support on x86. ARM64 support will be addressed in a separate RFC.
>>
>> Command line to test the CXL reset on a capable device:
>>     echo 1 > /sys/bus/pci/devices/<pci_device>/cxl_reset
>>
>> Basic cxl_reset testing was done on a CXL Type-2 device: writing to the
>> sysfs attribute, exercising the DVSEC reset sequence including WB+I and
>> init reset, restore. Further testing is in progress.
>>
>> This series is based on v7.0-rc1.
>>
>> Srirangan Madhavan (7):
>>   PCI: Add CXL DVSEC reset and capability register definitions
>>   PCI: Export pci_dev_save_and_disable() and pci_dev_restore()
>>   cxl: Add memory offlining and cache flush helpers
>>   cxl: Add multi-function sibling coordination for CXL reset
>>   cxl: Add CXL DVSEC reset sequence and flow orchestration
>>   cxl: Add cxl_reset sysfs interface for PCI devices
>>   Documentation: ABI: Add CXL PCI cxl_reset sysfs attribute
>>
>>  Documentation/ABI/testing/sysfs-bus-pci |  22 +
>>  drivers/cxl/core/core.h                 |   2 +
>>  drivers/cxl/core/pci.c                  | 537 ++++++++++++++++++++++++
>>  drivers/cxl/core/port.c                 |   3 +
>>  drivers/pci/pci.c                       |  21 +-
>>  include/linux/pci.h                     |   3 +
>>  include/uapi/linux/pci_regs.h           |  14 +
>>  7 files changed, 600 insertions(+), 2 deletions(-)
>>
>> base-commit: 6de23f81a5e0
> 
> The commit is 7.0-rc1. But b4 shazam seems to fail when attempting to apply.
> 
> Applying: PCI: Add CXL DVSEC reset and capability register definitions
> Patch failed at 0001 PCI: Add CXL DVSEC reset and capability register definitions
> error: patch failed: include/uapi/linux/pci_regs.h:1349
> error: include/uapi/linux/pci_regs.h: patch does not apply
> 

nm. I need to apply the save/restore series first. The base-commit should not be the v7.1-rc1 commit. 
> 
>> --
>> 2.43.0
>>
> 
>