Re: [PATCH v5 0/7] cxl: Support mixed-granularity region interleaves

[Alison Schofield <alison.schofield@intel.com>]

On Wed, Sep 16, 2026 at 08:19:01PM +0200, Robert Richter wrote:
> On 03.09.26 16:23:42, Alison Schofield wrote:
> > 
> > JonathanC, I kept your tags on Patches 2,5.
> > 
> > RobertR, Same comment as in v4. I've dropped the Originally-by tags since the
> > implementation no longer carries the selector-bit approach from your original
> > patch. Let me know what authorship tags you'd like.
> 
> Fine with me.
> 
> The series is much simpler than v3 now. Though, I believe the selector
> bit approach removes the limitations described, makes implemenation
> easier and removes additional checks needed. Will take a look how that
> could work and also give this series some testing.
> 
> Thanks for driving this.

Hi Robert,

Thanks for reviewing!

Yes, the series is much simpler now. In v3 we explored the more general selector-bit
model, but as you pointed out then, there isn't a single decoder granularity to derive
for the general case without defining stricter assignment rules. That led to making
the restriction explicit in v4 and limiting support to the monotonic coarse-to-fine
configurations.

The actual use case driving this series is 6- and 12-way regions behind a 3-way host
bridge. The monotonic power-of-two cases fall naturally out of the same implementation.

The CXL driver does not need to implement every configuration the spec permits, but 
rather adds support as use cases appear.

Do you know of a platform or user requirement that needs these configurations?

A few of your responses in this set appear to expand the supported configs beyond the
current scope. I'll respond to those individually, but wanted to raise the general
concern here first. We need to bottom out on the requirements before adding more
cases to the series.


-- Alison

> 
> -Robertx
> 
> > Alison Schofield (7):
> >   Documentation/cxl: Describe mixed-granularity regions
> >   cxl/region: Warn on user region position mismatch
> >   cxl/region: Generalize endpoint position mapping
> >   cxl/region: Name the interleave locals in cxl_port_setup_targets()
> >   cxl/region: Support mixed-granularity auto regions
> >   cxl/region: Support mixed-granularity user created regions
> >   cxl/test: Add a topology to test mixed-granularity regions
> > 
> >  .../driver-api/cxl/linux/cxl-driver.rst       | 153 +++++++
> >  drivers/cxl/core/region.c                     | 247 +++++++----
> >  tools/testing/cxl/test/cxl.c                  | 410 +++++++++++++++++-
> >  3 files changed, 698 insertions(+), 112 deletions(-)
> > 
> > 
> > base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
> > -- 
> > 2.37.3
> >