Programming HDM decoders

Programming HDM decoders

[Shesha Bhushan Sreenivasamurthy]

Hello all,
Section 9.13.3 of CXL3.0 says "Program the HDM decoders appropriately for each region’s base and length from
Get Dynamic Capacity Configuration data" and "Get Dynamic Capacity" which contains the start DPA and length of the extents. How is this DPA used in programming HDM decoders ?

Thanks,
Shesha.

RE: Programming HDM decoders

[Dan Williams]

Shesha Bhushan Sreenivasamurthy wrote:
> Hello all,
> Section 9.13.3 of CXL3.0 says "Program the HDM decoders appropriately
> for each region’s base and length from Get Dynamic Capacity
> Configuration data" and "Get Dynamic Capacity" which contains the
> start DPA and length of the extents. How is this DPA used in
> programming HDM decoders ?

See Figure 9-24. DCD DPA Space Example. You can think of those regions
as similar to how the driver handles RAM and PMEM regions. As far as
programming decoders the flow is the same for DCD regions as it is for
any other region. The distinction for DCD is that the DPA assigned to
the decoder additionally has a state of 'populated' or 'unpopulated' by
extents whereas RAM and PMEM are always represented by a single
'populated' extent.

The decoder programming flow is described in the cover letter for the
series that added region provisioning for PMEM:

https://lore.kernel.org/all/165784324066.1758207.15025479284039479071.stgit@dwillia2-xfh.jf.intel.com/

Another resource is the source for "cxl create-region":

https://github.com/pmem/ndctl/blob/main/cxl/region.c#L544

Lastly the driver-writer's guide also talks about the region creation
flow:

https://www.intel.com/content/www/us/en/content-details/643805/cxl-memory-device-sw-guide.html

...see Section 2.6 Memory Provisioning.