Re: [PATCH v8 3/9] dax/hmem: Request cxl_acpi and cxl_pci before walking Soft Reserved ranges

[Dan Williams]

Koralahalli Channabasappa, Smita wrote:
[..]
> > As I learned from Keith's recent CXL_PMEM dependency fix for CXL_ACPI
> > [1], this wants to be:
> > 
> > depends on DEV_DAX_HMEM || !DEV_DAX_HMEM
> > depends on CXL_ACPI || !CXL_ACPI
> > depends on CXL_PCI || !CXL_PCI
> > 
> > ...to make sure that DEV_DAX_CXL can never be built-in unless all of its
> > dependencies are built-in.
> > 
> > [1]: http://lore.kernel.org/69aa341fcf526_6423c1002c@dwillia2-mobl4.notmuch
> > 
> > At this point I am wondering if all of the feedback I have for this
> > series should just be incremental fixes. I also want to have a canned
> > unit test that verifies the base expectations. That can also be
> > something I reply incrementally.
> 
> Two things on the Kconfig change:
> 
> When DEV_DAX_HMEM = y and CXL_ACPI = m and CXL_PCI = m

Right, this should not be possible. The patch I am testing moves the
optional CXL dependencies to DEV_DAX_HMEM where they belong. I
mistakenly showed them against DEV_DAX_CXL in my comment.

> 1. Regarding switching from >= to || ! pattern:
> 
> The >= pattern disabled DEV_DAX_CXL entirely when DEV_DAX_HMEM = y and 
> CXL_ACPI/CXL_PCI = m. So, HMEM unconditionally owned all ranges - the 
> CXL deferral path is never entered.

That is one of the broken configurations to fix. It should never be
possible to set DEV_DAX_HMEM=y unless CXL_ACPI and CXL_PCI are both
disabled or both built-in.

> When DEV_DAX_HMEM = y and CXL core is built as a module hmem.c calls 
> cxl_region_contains_resource() which lives in cxl_core.ko causing an 
> undefined reference at link time.

Yes, I hit this as well and requires another CXL_BUS dependency.