Re: [PATCH v1 19/29] cxl/region: Use endpoint's HPA range to find the port's decoder

[Robert Richter]

On 07.01.25 17:18:49, Gregory Price wrote:
> On Tue, Jan 07, 2025 at 03:10:05PM +0100, Robert Richter wrote:
> > For the implementation of address translation it might not be possible
> > to determine the root decoder in the early enumeration state since the
> > SPA range is still unknown. Instead, the endpoint's HPA range is known
> > and from there the topology can be traversed up to the root port while
> > the memory range is adjusted from one memory domain to the next up to
> > the root port.
> > 
> > In a first step, use endpoint's HPA range to find the port's decoder.
> > Without address translation there is HPA == SPA. Then, the HPA range
> > of the endpoint can be used instead of the root decoder's range as
> > both are the same.
> > 
> > Signed-off-by: Robert Richter <rrichter@xxxxxxx>
> 
> I'll make a note to test up to this patch in particular in HPA==SPA
> mode without the follow ons.
> 
> The functional change here is the move from cxlr->params to
> cxled->cxld.hpa_range. 
> 
> What was the likely value of cxlr->params previously? Undefined?

The region's hpa range was set up with the same values. Thus it can be
used interchangeable.

Call chain:

cxl_endpoint_decoder_add
  hpa = &cxled->cxld.hpa_range;
  cxl_find_region_by_range(..., hpa);
    match_region_by_range(..., hpa);
  construct_region
    hpa = &cxled->cxld.hpa_range;
    *res = DEFINE_RES_MEM_NAMED(hpa->start, range_len(hpa), ...)
  attach_target
    cxl_region_attach
      cxl_region_attach_position
        cxl_port_attach_region
          cxl_find_decoder_early
            hpa = &cxled->cxld.hpa_range
            match_auto_decoder(..., hpa)

Note I have moved out the switch to spa_range of "[PATCH v1 15/29]
cxl/region: Use an endpoint's SPA range to find a region" to a later
patch for a better understanding of the changes, but technically it is
the same as there is still spa == hpa at this point.

> 
> Otherwise I don't immediately see any issues.
> 
> Reviewed-by: Gregory Price <gourry@xxxxxxxxxx>

Thanks,

-Robert