Re: [PATCH 4/5] cxl: Set type of region to that of the first endpoint

[Dan Williams]

Huang, Ying wrote:
> Dan Williams <dan.j.williams@xxxxxxxxx> writes:
> 
> > Huang Ying wrote:
> 
> [snip]
> 
> >> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> >> index 21b877d8582f..d709738ada61 100644
> >> --- a/drivers/cxl/core/region.c
> >> +++ b/drivers/cxl/core/region.c
> >> @@ -1926,7 +1926,10 @@ static int cxl_region_attach(struct cxl_region *cxlr,
> >>  		return -ENXIO;
> >>  	}
> >>  
> >> -	if (cxled->cxld.target_type != cxlr->type) {
> >> +	/* Set the type of region to that of the first endpoint */
> >> +	if (cxlr->type == CXL_DECODER_INVALID) {
> >> +		cxlr->type = cxled->cxld.target_type;
> >> +	} else if (cxled->cxld.target_type != cxlr->type) {
> >
> > No, the type of the region is determined by the caller and should be
> > gated by the region capability. For type-2 region creation I doubt
> > userspace is going to be creating those vs the accelerator so this all
> > seems backwards to me.
> 
> How do we determine the type of the endpoint?  Specify it in type2/type3
> device driver?

Why does the endpoint type matter? Memory expansion can be supported by
HDM-D[B], and an accelerator could have one or more HDM-H decoders.

> If so, we will specify the type of both the endpoint and the region in
> type2/type3 device driver.  Then, why not only specify the type of the
> endpoint?  The type of region can be determined from the type of the
> endpoint.

Because CXL HDM protocol is per decoder not per device.