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

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Date:   Tue, 25 Oct 2022 01:50:34 +0200
From:   Robert Richter <rrichter@....com>
To:     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

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.

>     Then we can figure out what to do
>     about RCDs that choose not to implement the HDM decoder capability which
>     was forbidden in CXL 2.0, but now allowed in CXL 3.0.
> 
> Hi Robert. As follow on to your work, I'm also working on reworking the hdm
> decoder enumeration. I have this table from Dan where rr - range register exist
> but not setup, RR - range register exist and setup, hdm - HDM decoder exist but
> not programmed, HDM - HDM decoders exist and programmed. And I'm trying to
> refactor the current code to cover all those scenarios:
> 
>          rr             RR               rr hdm          rr HDM          RR hdm         RR HDM
> D2       unsupported    emulate RR       enable HDM      keep HDM        enable HDM     keep HDM
> D1       unsupported    emulate RR       enable HDM      keep HDM        enable HDM     keep HDM
> 
> The current test device I have that's attached to RCH host, I'm seeing the RR
> has setup a single range, but none of the HDM decoders are programmed.
> 

Right, HDM decoder init need to be changed next.

Thanks,

-Robert