Re: [PATCH v3 08/14] cxl/region: HB port config verification

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

On Thu, 27 Jan 2022 16:27:01 -0800
Ben Widawsky <ben.widawsky@intel.com> wrote:

> Host bridge root port verification determines if the device ordering in
> an interleave set can be programmed through the host bridges and
> switches.
> 
> The algorithm implemented here is based on the CXL Type 3 Memory Device
> Software Guide, chapter 2.13.15. The current version of the guide does
> not yet support x3 interleave configurations, and so that's not
> supported here either.
> 
> Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>


> +static struct cxl_dport *get_rp(struct cxl_memdev *ep)
> +{
> +	struct cxl_port *port, *parent_port = port = ep->port;
> +	struct cxl_dport *dport;
> +
> +	while (!is_cxl_root(port)) {
> +		parent_port = to_cxl_port(port->dev.parent);
> +		if (parent_port->depth == 1)
> +			list_for_each_entry(dport, &parent_port->dports, list)
> +				if (dport->dport == port->uport->parent->parent)
> +					return dport;
> +		port = parent_port;
> +	}
> +
> +	BUG();

I know you mentioned you were reworking this patch set anyway, but
I thought I'd give some quick debugging related feedback.

When running against a single switch in qemu (patches out once
things are actually working), I hit this BUG()
printing dev_name for the port->uport->parent->parent gives
pci0000:0c but the matches are sort against
0000:0c:00.0 etc

So looks like one too many levels of parent in this case at least.

The other bug I haven't chased down yet is that if we happen
to have downstream ports of the switch with duplicate ids
(far too easy to do in QEMU as port_num is an optional
parameter for switch DS ports) it's detected and the probe fails
- but then it tries again and we get an infinite loop of new
ports being created and failing to probe...
I'll get back this one once I have it working with
a valid switch config.

Jonathan

> +	return NULL;
> +}