Re: [PATCH v5 3/5] cxl/region: Introduce SPA to DPA address translation

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

On Mon,  4 Aug 2025 01:00:11 -0700
alison.schofield@intel.com wrote:

> From: Alison Schofield <alison.schofield@intel.com>
> 
> Add infrastructure to translate System Physical Addresses (SPA) to
> Device Physical Addresses (DPA) within CXL regions. This capability
> will be used by follow-on patches that add poison inject and clear
> operations at the region level.
> 
> The SPA-to-DPA translation process follows these steps:
> 1. Apply root decoder transformations (SPA to HPA) if configured.
> 2. Extract the position in region interleave from the HPA offset.
> 3. Extract the DPA offset from the HPA offset.
> 4. Use position to find endpoint decoder.
> 5. Use endpoint decoder to find memdev and calculate DPA from offset.
> 6. Return the result - a memdev and a DPA.
> 
> It is Step 1 above that makes this a driver level operation and not
> work we can push to user space. Rather than exporting the XOR maps for
> root decoders configured with XOR interleave, the driver performs this
> complex calculation for the user.
> 
> Steps 2 and 3 follow the CXL Spec 3.2 Section 8.2.4.20.13
> Implementation Note: Device Decode Logic.
> 
> These calculations mirror much of the logic introduced earlier in DPA
> to SPA translation, see cxl_dpa_to_hpa(), where the driver needed to
> reverse the spec defined 'Device Decode Logic'.
> 
> Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>