Re: [PATCH v3 11/11] cxl: Enable AMD Zen5 address translation using ACPI PRMT

[Gregory Price <gourry@gourry.net>]

On Fri, Sep 26, 2025 at 06:59:40PM +0200, Robert Richter wrote:
> On 24.09.25 13:09:46, Gregory Price wrote:
> > On Fri, Sep 12, 2025 at 04:45:13PM +0200, Robert Richter wrote:
> > > +static void cxl_prm_init(struct cxl_port *port)
> > > +{
> > > +	u64 spa;
> > > +	struct prm_cxl_dpa_spa_data data = { .out = &spa, };
> > > +	int rc;
> > > +
> > > +	if (!check_prm_address_translation(port))
> > > +		return;
> > > +
> > > +	/* Check kernel (-EOPNOTSUPP) and firmware support (-ENODEV) */
> > > +	rc = acpi_call_prm_handler(prm_cxl_dpa_spa_guid, &data);
> > > +	if (rc == -EOPNOTSUPP || rc == -ENODEV)
> > > +		return;
> > > +
> > > +	port->to_hpa = cxl_prm_to_hpa;
> > > +
> > > +	dev_dbg(port->host_bridge, "PRM address translation enabled for %s.\n",
> > > +		dev_name(&port->dev));
> > > +}
> > 
> > Is it possible that the PRMT function is present but uninitialize?
> > For example if expanders are not in a normalized address mode.
> > 
> > This code would likely still add the to_hpa() function reference even
> > if the underlying PRMT function hasn't been set up for translation.
> 
> At this point during init, it is not yet possible to determine
> normalized address mode. Endpoint and hdm decoders are still unknown.
> Thus, PRM is enabled for the port. Later, during region setup, there is
> a check for that while determining the region's HPA range. Addresses
> are translated and ranges adjusted only if needed. Once the ranges are
> set up, no further PRM handler calls are executed.
>

Right, but that errors out if address translation fails (below).

Is this code missing a check for the endpoint_decoder.start==0?

static int setup_address_translation(struct cxl_endpoint_decoder *cxled,
                                     struct cxl_region_context *ctx)
{
...
        /* Translate HPA range to SPA. */
        range.start = port->to_hpa(cxld, range.start);
        range.end = port->to_hpa(cxld, range.end);

        if (range.start == ULLONG_MAX || range.end == ULLONG_MAX) {
                dev_warn(&port->dev,
                        "CXL address translation: Failed to translate HPA range: %#llx-%#llx:%#llx-%#llx(%s)\n",
                        range.start, range.end, ctx->hpa_range.start,
                        ctx->hpa_range.end, dev_name(&cxld->dev));
                return -ENXIO;
        }
...
}


static int setup_region_params(struct cxl_endpoint_decoder *cxled,
                               struct cxl_region_context *ctx)
{          
...
        rc = setup_address_translation(cxled, ctx);
...
}


int cxl_add_to_region(struct cxl_endpoint_decoder *cxled)
{
...
        rc = setup_region_params(cxled, &ctx);
        if (rc)
                return rc;
}