linux-kernel - Re: [PATCH v2 06/12] cxl/acpi: Extract component registers of restricted hosts from RCRB

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Date:   Mon, 24 Oct 2022 16:57:24 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Robert Richter <rrichter@....com>,
        Dave Jiang <dave.jiang@...el.com>
CC:     Dan Williams <dan.j.williams@...el.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        "Ira Weiny" <ira.weiny@...el.com>,
        Ben Widawsky <bwidawsk@...nel.org>,
        <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        "Davidlohr Bueso" <dave@...olabs.net>,
        Terry Bowman <terry.bowman@....com>
Subject: Re: [PATCH v2 06/12] cxl/acpi: Extract component registers of
 restricted hosts from RCRB

Robert Richter wrote:
> On 24.10.22 16:23:39, Dave Jiang wrote:
> > On 10/24/2022 3:37 PM, Dan Williams wrote:
> >     Dan Williams wrote:
> >         Robert Richter wrote:
> 
> >             Ok, I see where to go here. Could you point me to Dave's postings you
> >             are referring to? I checked linux-cxl and could not find anything
> >             related to RCRB or that changes regs.c.
> > 
> >         He was in the middle of tidying them when you posted your series, but I
> >         think it would not hurt to push them to a git tree so you can grab the
> >         bits and pieces you want.
> > 
> >         Dave?
> > 
> >     Looks like the list delivery is backed up, so I added Dave to the Cc:.
> > 
> >     He pushed:
> > 
> >     https://git.kernel.org/pub/scm/linux/kernel/git/djiang/linux.git/log/?h=cxl-rch
> > 
> >     ...which was his original attempt and:
> > 
> >     https://git.kernel.org/pub/scm/linux/kernel/git/djiang/linux.git/log/?h=cxl-rch-robert
> > 
> >     ...which was an attempt to rebase on top of your bits.
> > 
> >     The common RCRB mapping function is here:
> > 
> >     https://git.kernel.org/pub/scm/linux/kernel/git/djiang/linux.git/commit/?h=cxl-rch-robert&id=5be44cad37972517dae6a79001080ccfbdb67c49
> 
> Thanks for the pointers.
> 
> > 
> >     I think the path forward is to build on that common RCRB code, fix
> >     cxl_acpi to register the pci host bridge device instead of the APCI
> >     device as the dport device, and then rely on a flag to skip over
> >     devm_enumerate_cxl_ports() in favor of just calling cxl_mem_find_port()
> >     directly in the RCIEP / RCH case.
> 
> Yes, we can completely skip devm_enumerate_cxl_ports() now. Though, I
> am not convinced on using the pci host bridge as dport_dev as RCD and
> non-RCD mode will diverge too much then. Looking into details here.

Oh, I disagree with the initial implementation Dave had here. Both cases
should be specifying the bridge device as the dport. That's a fixup that
can go in now even without the RCD support.

As it is the tooling needs to jump through the physical_node attribute
to provide the useful information in cxl list:

# cxl list -BTu -b ACPI.CXL
{
  "bus":"root0",
  "provider":"ACPI.CXL",
  "nr_dports":1,
  "dports":[
    {
      "dport":"ACPI0016:00",
      "alias":"pci0000:34",
      "id":"0x34"
    }
  ]
}

...and I think that should just swap to this in all cases:

# cxl list -BTu -b ACPI.CXL
{
  "bus":"root0",
  "provider":"ACPI.CXL",
  "nr_dports":1,
  "dports":[
    {
      "dport":"pci0000:34",
      "alias":"ACPI0016:00",
      "id":"0x34"
    }
  ]
}