Re: [PATCH v5 7/7] cxl/test: Add a topology to test mixed-granularity regions

[Jonathan Cameron <jic23@kernel.org>]

On Thu,  3 Sep 2026 16:23:49 -0700
Alison Schofield <alison.schofield@intel.com> wrote:

> Add a cxl_test topology for mixed-granularity region testing.
> 
> modprobe cxl_test mixed_gran_regions=1 creates three host bridges, two
> root ports per host bridge, one switch per root port, and two endpoints
> per switch, for twelve endpoints total.
> 
> Two root ports per host bridge is what makes the interleaving levels
> selectable. A region built from one endpoint per root port interleaves
> at the host bridge and passes through the switch; a region built from
> both endpoints below a single root port passes through the host bridge
> and interleaves at the switch; a region using every endpoint
> interleaves at both. The CXL Specification lists those as distinct
> legal configurations, so the choice of member endpoints, rather than a
> second topology, selects which one is under test.
> 
> Three CFMWS windows are added:
> 
> 1) A 2-way window at 4K over two host bridges, hosting an 8-way region
> at 1K and a 4-way region at 2K.
> 
> 2) A 3-way window at 512 over three host bridges, hosting a 6-way
> region at 256: CXL 4.0 Table 9-7 rows 2 and 3.
> 
> 3) A 3-way window at 1K over three host bridges, hosting a 12-way
> region at 256: CXL 4.0 Table 9-6 row 7. That row is the composition
> the documentation contrasts with the unsupported row 6, and reaching it
> needs a root granularity four times the region granularity.
> 
> Each window also hosts a same-granularity region at its own ways and
> granularity. The 2-way window at 4K hosts 4-way and 8-way regions at 4K as
> well; the span identity allows the 3-way windows only their own width.
> 
> Register every mock device through cxl_mock_platform_device_add() so
> the mock array is populated before platform_device_add(), matching the
> ordering the rest of cxl_test relies on to avoid the endpoint-probe
> race in commit d90f236f8b9e ("cxl/test: Update mock dev array before
> calling platform_device_add()").
> 
> NULL-check the legacy topology arrays in the mock device and mock port
> lookups, which are left empty when mixed_gran_regions=1 selects the new
> topology.
> 
> The default and existing special module params are unaffected.
> 
> Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Hi Alison,

Sorry, no tag for this, but just because I can't remember enough about
how the tests work (if I ever really understood!) and don't want to
spend the rest of today working it out again :(  
FWIW, I didn't spot anything wrong from a quick look but I'm not feeling
confident to review this.

Jonathan