Re: [PATCH 40/46] cxl/region: Attach endpoint decoders

[Dan Williams <dan.j.williams@intel.com>]

Jonathan Cameron wrote:
> On Thu, 23 Jun 2022 21:19:44 -0700
> Dan Williams <dan.j.williams@intel.com> wrote:
> 
> > CXL regions (interleave sets) are made up of a set of memory devices
> > where each device maps a portion of the interleave with one of its
> > decoders (see CXL 2.0 8.2.5.12 CXL HDM Decoder Capability Structure).
> > As endpoint decoders are identified by a provisioning tool they can be
> > added to a region provided the region interleave properties are set
> > (way, granularity, HPA) and DPA has been assigned to the decoder.
> > 
> > The attach event triggers several validation checks, for example:
> > - is the DPA sized appropriately for the region
> > - is the decoder reachable via the host-bridges identified by the
> >   region's root decoder
> > - is the device already active in a different region position slot
> > - are there already regions with a higher HPA active on a given port
> >   (per CXL 2.0 8.2.5.12.20 Committing Decoder Programming)
> > 
> > ...and the attach event affords an opportunity to collect data and
> > resources relevant to later programming the target lists in switch
> > decoders, for example:
> > - allocate a decoder at each cxl_port in the decode chain
> > - for a given switch port, how many the region's endpoints are hosted
> >   through the port
> > - how many unique targets (next hops) does a port need to map to reach
> >   those endpoints
> > 
> > The act of reconciling this information and deploying it to the decoder
> > configuration is saved for a follow-on patch.
> > 
> > Co-developed-by: Ben Widawsky <bwidawsk@kernel.org>
> > Signed-off-by: Ben Widawsky <bwidawsk@kernel.org>
> > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> > ---
> >  drivers/cxl/core/core.h   |   7 +
> >  drivers/cxl/core/port.c   |  10 +-
> >  drivers/cxl/core/region.c | 338 +++++++++++++++++++++++++++++++++++++-
> >  drivers/cxl/cxl.h         |  20 +++
> >  drivers/cxl/cxlmem.h      |   5 +
> >  5 files changed, 372 insertions(+), 8 deletions(-)
> > 
> 
> 
> > diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> > index 4830365f3857..65bf84abad57 100644
> > --- a/drivers/cxl/core/region.c
> > +++ b/drivers/cxl/core/region.c
> > @@ -428,6 +428,254 @@ static size_t show_targetN(struct cxl_region *cxlr, char *buf, int pos)
> >  	return rc;
> >  }
> >  
> 
> > +
> > +static struct cxl_region_ref *alloc_region_ref(struct cxl_port *port,
> > +					       struct cxl_region *cxlr)
> > +{
> > +	struct cxl_region_ref *cxl_rr;
> > +
> > +	cxl_rr = kzalloc(sizeof(*cxl_rr), GFP_KERNEL);
> > +	if (!cxl_rr)
> > +		return NULL;
> > +	cxl_rr->port = port;
> > +	cxl_rr->region = cxlr;
> > +	xa_init(&cxl_rr->endpoints);
> > +	return cxl_rr;
> > +}
> > +
> > +static void free_region_ref(struct cxl_region_ref *cxl_rr)
> > +{
> > +	struct cxl_port *port = cxl_rr->port;
> > +	struct cxl_region *cxlr = cxl_rr->region;
> > +	struct cxl_decoder *cxld = cxl_rr->decoder;
> > +
> > +	dev_WARN_ONCE(&cxlr->dev, cxld->region != cxlr, "region mismatch\n");
> > +	if (cxld->region == cxlr) {
> > +		cxld->region = NULL;
> > +		put_device(&cxlr->dev);
> > +	}
> > +
> > +	xa_erase(&port->regions, (unsigned long)cxlr);
> 
> Why do we have things in a free_ function that aren't simply removing things
> created in the alloc()?  I'd kind of expect this to be in a cxl_rr_del() or similar.

Fixed it the other way by just open-coding cxl_rr_add() into
alloc_region_ref(). There was no good reason to have them as separate
steps.

> 
> > +	xa_destroy(&cxl_rr->endpoints);
> > +	kfree(cxl_rr);
> > +}
> > +
> > +static int cxl_rr_add(struct cxl_region_ref *cxl_rr)
> > +{
> > +	struct cxl_port *port = cxl_rr->port;
> > +	struct cxl_region *cxlr = cxl_rr->region;
> > +
> > +	return xa_insert(&port->regions, (unsigned long)cxlr, cxl_rr,
> > +			 GFP_KERNEL);
> > +}
> > +
> > +static int cxl_rr_ep_add(struct cxl_region_ref *cxl_rr,
> > +			 struct cxl_endpoint_decoder *cxled)
> > +{
> > +	int rc;
> > +	struct cxl_port *port = cxl_rr->port;
> > +	struct cxl_region *cxlr = cxl_rr->region;
> > +	struct cxl_decoder *cxld = cxl_rr->decoder;
> > +	struct cxl_ep *ep = cxl_ep_load(port, cxled_to_memdev(cxled));
> > +
> > +	rc = xa_insert(&cxl_rr->endpoints, (unsigned long)cxled, ep,
> > +			 GFP_KERNEL);
> > +	if (rc)
> > +		return rc;
> > +	cxl_rr->nr_eps++;
> > +
> > +	if (!cxld->region) {
> > +		cxld->region = cxlr;
> > +		get_device(&cxlr->dev);
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static int cxl_port_attach_region(struct cxl_port *port,
> > +				  struct cxl_region *cxlr,
> > +				  struct cxl_endpoint_decoder *cxled, int pos)
> > +{
> > +	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> > +	struct cxl_ep *ep = cxl_ep_load(port, cxlmd);
> > +	struct cxl_region_ref *cxl_rr = NULL, *iter;
> > +	struct cxl_region_params *p = &cxlr->params;
> > +	struct cxl_decoder *cxld = NULL;
> > +	unsigned long index;
> > +	int rc = -EBUSY;
> > +
> > +	lockdep_assert_held_write(&cxl_region_rwsem);
> 
> This function is complex enough that maybe it would benefit from
> some saying what each part is doing.

...added a kdoc block:

/**
 * cxl_port_attach_region() - track a region's interest in a port by endpoint
 * @port: port to add a new region reference 'struct cxl_region_ref'
 * @cxlr: region to attach to @port
 * @cxled: endpoint decoder used to create or further pin a region reference
 * @pos: interleave position of @cxled in @cxlr
 *
 * The attach event is an opportunity to validate CXL decode setup
 * constraints and record metadata needed for programming HDM decoders,
 * in particular decoder target lists.
 *
 * The steps are:
 * - validate that there are no other regions with a higher HPA already
 *   associated with @port
 * - establish a region reference if one is not already present
 *   - additionally allocate a decoder instance that will host @cxlr on
 *     @port
 * - pin the region reference by the endpoint
 * - account for how many entries in @port's target list are needed to
 *   cover all of the added endpoints.
 */

> 
> > +
> > +	xa_for_each(&port->regions, index, iter) {
> > +		struct cxl_region_params *ip = &iter->region->params;
> > +
> > +		if (iter->region == cxlr)
> > +			cxl_rr = iter;
> > +		if (ip->res->start > p->res->start) {
> > +			dev_dbg(&cxlr->dev,
> > +				"%s: HPA order violation %s:%pr vs %pr\n",
> > +				dev_name(&port->dev),
> > +				dev_name(&iter->region->dev), ip->res, p->res);
> > +			return -EBUSY;
> > +		}
> > +	}
> > +
> > +	if (cxl_rr) {
> > +		struct cxl_ep *ep_iter;
> > +		int found = 0;
> > +
> > +		cxld = cxl_rr->decoder;
> > +		xa_for_each(&cxl_rr->endpoints, index, ep_iter) {
> > +			if (ep_iter == ep)
> > +				continue;
> > +			if (ep_iter->next == ep->next) {
> > +				found++;
> > +				break;
> > +			}
> > +		}
> > +
> > +		/*
> > +		 * If this is a new target or if this port is direct connected
> > +		 * to this endpoint then add to the target count.
> > +		 */
> > +		if (!found || !ep->next)
> > +			cxl_rr->nr_targets++;
> > +	} else {
> > +		cxl_rr = alloc_region_ref(port, cxlr);
> > +		if (!cxl_rr) {
> > +			dev_dbg(&cxlr->dev,
> > +				"%s: failed to allocate region reference\n",
> > +				dev_name(&port->dev));
> > +			return -ENOMEM;
> > +		}
> > +		rc = cxl_rr_add(cxl_rr);
> > +		if (rc) {
> > +			dev_dbg(&cxlr->dev,
> > +				"%s: failed to track region reference\n",
> > +				dev_name(&port->dev));
> > +			kfree(cxl_rr);
> > +			return rc;
> > +		}
> > +	}
> > +
> > +	if (!cxld) {
> > +		if (port == cxled_to_port(cxled))
> > +			cxld = &cxled->cxld;
> > +		else
> > +			cxld = cxl_region_find_decoder(port, cxlr);
> > +		if (!cxld) {
> > +			dev_dbg(&cxlr->dev, "%s: no decoder available\n",
> > +				dev_name(&port->dev));
> > +			goto out_erase;
> > +		}
> > +
> > +		if (cxld->region) {
> > +			dev_dbg(&cxlr->dev, "%s: %s already attached to %s\n",
> > +				dev_name(&port->dev), dev_name(&cxld->dev),
> > +				dev_name(&cxld->region->dev));
> > +			rc = -EBUSY;
> > +			goto out_erase;
> > +		}
> > +
> > +		cxl_rr->decoder = cxld;
> > +	}
> > +
> > +	rc = cxl_rr_ep_add(cxl_rr, cxled);
> > +	if (rc) {
> > +		dev_dbg(&cxlr->dev,
> > +			"%s: failed to track endpoint %s:%s reference\n",
> > +			dev_name(&port->dev), dev_name(&cxlmd->dev),
> > +			dev_name(&cxld->dev));
> > +		goto out_erase;
> > +	}
> > +
> > +	return 0;
> > +out_erase:
> > +	if (cxl_rr->nr_eps == 0)
> > +		free_region_ref(cxl_rr);
> > +	return rc;
> > +}
> > +
> 
> >  
> >  static void cxl_region_detach(struct cxl_endpoint_decoder *cxled)
> >  {
> > +	struct cxl_port *iter, *ep_port = cxled_to_port(cxled);
> >  	struct cxl_region *cxlr = cxled->cxld.region;
> >  	struct cxl_region_params *p;
> >  
> > @@ -481,6 +811,10 @@ static void cxl_region_detach(struct cxl_endpoint_decoder *cxled)
> >  	p = &cxlr->params;
> >  	get_device(&cxlr->dev);
> >  
> > +	for (iter = ep_port; !is_cxl_root(iter);
> > +	     iter = to_cxl_port(iter->dev.parent))
> > +		cxl_port_detach_region(iter, cxlr, cxled);
> > +
> >  	if (cxled->pos < 0 || cxled->pos >= p->interleave_ways ||
> >  	    p->targets[cxled->pos] != cxled) {
> >  		struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> > @@ -491,6 +825,8 @@ static void cxl_region_detach(struct cxl_endpoint_decoder *cxled)
> >  		goto out;
> >  	}
> >  
> > +	if (p->state == CXL_CONFIG_ACTIVE)
> 
> I 'think' the state is either CXL_CONFIG_ACTIVE or CXL_CONFIG_INTERLEAVE_ACTIVE,
> so you could set this unconditionally.  A comment here on permissible
> states would be useful for future reference.

cxl_region_detach() should not care if the region state is idle. Not
that it will happen in the current code, but the only expectation is
that if the region is active and a endpoint departs it must be
downgraded in config state. CXL_CONFIG_IDLE is permissible, although not
expected. I do not think a comment is needed if the "if (p->state ==
CXL_CONFIG_ACTIVE)" check stays.

> 
> > +		p->state = CXL_CONFIG_INTERLEAVE_ACTIVE;
> >  	p->targets[cxled->pos] = NULL;
> >  	p->nr_targets--;
> 
>