Re: [RFC PATCH 00/18] Initial CXL.cache device support

[Dave Jiang <dave.jiang@intel.com>]

On 8/12/25 2:29 PM, Ben Cheatham wrote:
> This patch series adds initial CXL.cache support. What I have here only
> allows for adding a cache device to the system, programming/validating
> the system configuration with respect to cache devices, and some basic
> cache reporting/management.
> 
> The general philosophy is to have an endpoint/vendor-specific driver
> that runs through the same steps of adding a cxl_memdev, but for the
> cache portion of the device (both type 1 & 2). Getting cache support for
> a CXL device should be as simple as: get cache information, set up the
> memory region (see below), and then calling devm_cxl_add_cachedev().
> 
> There's a couple of things missing from this set:
> 
> 1) Missing an endpoint driver
> 
> 	I plan on submitting a reference driver (type 1 or 2) with v1, I
> 	figured I'd send out what I have before going much further.

Hi Ben,

Don't mind getting this all sorted out and discussed. But we will need a real vendor device out there at some point as a user for all the code to be merged.

DJ

> 
> 2) Mapping/Reserving host memory used for CXL cache(s)
> 
> 	I'm thinking this will be handled by the endpoint driver, but I'm
> 	not sure what mechanism would be used and whether to integrate it
> 	with the cxl_cache/core. Any thoughts/ideas here are appreciated!
> 
> 3) RAS Support
> 
> 	Same situation as 1) above.
> 
> Some quick notes: The actual cache parts of this set are untested due
> to problems with my set up, but I did make sure nothing here breaks type
> 3 support. I'll have this fixed before sending out a v1. This series is
> based on the for-6.18/cxl-probe-order (commit 5e29cbd1077b) branch in
> the CXL repo, with v7 of Dave's deferred dport probe set on top [1]. I
> added Dave's set to help with getting around constraints with HDM
> decoders in CXL.cache device only configurations (see 08/18 for more).
> 
> Patch Breakdown:
> 	- 1 & 2: Preliminary changes for struct cxl_cachedev
> 	- 3: Add struct cxl_cachedev
> 	- 4-8: Preliminary changes for adding cache devices to port
> 	  hierarchy
> 	- 9: Function for getting CXL cache info
> 	- 10: cxl_cache driver (mirrors cxl_mem)
> 	- 11-16: Checking CXL.cache capabilities for system configuration
> 	  validity
> 	- 17-18: Cache device attributes
> 
> [1]:
> Link: https://lore.kernel.org/linux-cxl/20250714223527.461147-1-dave.jiang@intel.com/
> 
> Ben Cheatham (18):
>   cxl/mem: Change cxl_memdev_ops to cxl_dev_ops
>   cxl: Move struct cxl_dev_state definition
>   cxl/core: Add CXL.cache device struct
>   cxl: Replace cxl_mem_find_port() with cxl_dev_find_port()
>   cxl: Change cxl_ep_load() to use struct device * parameter
>   cxl/port, mem: Make adding an endpoint device type agnostic
>   cxl/port: Split endpoint port probe on device type
>   cxl/port: Update switch_port_probe() for CXL cache devices
>   cxl/core: Add function for getting CXL cache info
>   cxl/cache: Add cxl_cache driver
>   cxl/core: Add CXL snoop filter setup and checking
>   cxl/cache: Add CXL Cache ID Route Table mapping
>   cxl/cache: Implement Cache ID Route Table programming
>   cxl/cache: Add Cache ID Decoder capability mapping
>   cxl/cache: Implement Cache ID Decoder programming
>   cxl/cache: Add cache device counting for CXL ports
>   cxl/core: Add cache device attributes
>   cxl/core: Add cache device cache management attributes
> 
>  drivers/cxl/Kconfig         |  14 +
>  drivers/cxl/Makefile        |   2 +
>  drivers/cxl/cache.c         | 276 +++++++++++++++++++
>  drivers/cxl/core/Makefile   |   1 +
>  drivers/cxl/core/cachedev.c | 292 ++++++++++++++++++++
>  drivers/cxl/core/hdm.c      |  31 +++
>  drivers/cxl/core/memdev.c   |   2 +-
>  drivers/cxl/core/pci.c      | 134 ++++++++++
>  drivers/cxl/core/port.c     | 518 +++++++++++++++++++++++++++++++++---
>  drivers/cxl/core/region.c   |  25 +-
>  drivers/cxl/core/regs.c     |  28 ++
>  drivers/cxl/cxl.h           | 193 +++++++++++++-
>  drivers/cxl/cxlcache.h      |  42 +++
>  drivers/cxl/cxlmem.h        | 121 +--------
>  drivers/cxl/cxlpci.h        |  10 +
>  drivers/cxl/mem.c           |  14 +-
>  drivers/cxl/pci.c           |   2 +-
>  drivers/cxl/port.c          |  54 ++--
>  drivers/cxl/private.h       |   8 +-
>  19 files changed, 1569 insertions(+), 198 deletions(-)
>  create mode 100644 drivers/cxl/cache.c
>  create mode 100644 drivers/cxl/core/cachedev.c
>  create mode 100644 drivers/cxl/cxlcache.h
>