Re: [PATCH] cxl/port: Fix find_cxl_root() for RCDs and simplify it

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

Gregory Price wrote:
> On Wed, Mar 29, 2023 at 02:39:53PM -0700, Dan Williams wrote:
> > Gregory Price wrote:
> > > On Tue, Mar 28, 2023 at 11:36:17AM -0700, Dan Williams wrote:
> > > > The find_cxl_root() helper is used to lookup root decoders and other CXL
> > > > platform topology information for a given endpoint. It turns out that
> > > > for RCDs it has never worked. The result of find_cxl_root(&cxlmd->dev)
> > > > is always NULL for the RCH topology case because it expects to find a
> > > > cxl_port at the host-bridge. RCH topologies only have the root cxl_port
> > > > object with the host-bridge as a dport. While there are no reports of
> > > > this being a problem to date, by inspection region enumeration should
> > > > crash as a result of this problem, and it does in a local unit test for
> > > > this scenario.
> > > > 
> > > > However, an observation that ever since:
> > > > 
> > > > commit f17b558d6663 ("cxl/pmem: Refactor nvdimm device registration, delete the workqueue")
> > > > 
> > > > ...all callers of find_cxl_root() occur after the memdev connection to
> > > > the port topology has been established. That means that find_cxl_root()
> > > > can be simplified to a walk of the endpoint port topology to the root.
> > > > Switch to that arrangement which also fixes the RCD bug.
> > > > 
> > > > Fixes: a32320b71f08 ("cxl/region: Add region autodiscovery")
> > > > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> > [..]
> > > Is it expected that RCD's will fail when set to EFI_MEMORY_SP?  If
> > > that's the case, then this (and the other patch) look safe and do not
> > > produce regression.
> > > 
> > > Just want to capture this behavior, as it appears there may be other
> > > issues related to RCH/RCD combinations.
> > 
> > After I posted this fix testing revealed the need for a few more fixes,
> > now posted. Most importantly for accessing range register defined
> > regions is this new fix:
> > 
> > http://lore.kernel.org/r/168012575521.221280.14177293493678527326.stgit@dwillia2-xfh.jf.intel.com
> 
> Are these patches on top of an unpushed cxl branch? I'm having a hard
> time finding the base patch to apply these to.

Pushed a preview with all pending fixes applied here:

https://git.kernel.org/pub/scm/linux/kernel/git/cxl/cxl.git/log/?h=for-6.3/fixes