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

[Gregory Price <gregory.price@memverge.com>]

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.

Thanks for the help,
Gregory