linux-kernel - Re: [PATCH 11/15] cxl/acpi: Extract the host's component register base address from RCRB

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Date:   Tue, 6 Sep 2022 13:32:16 +0200
From:   Robert Richter <rrichter@....com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
CC:     Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Ben Widawsky <bwidawsk@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        <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>,
        Terry Bowman <terry.bowman@....com>
Subject: Re: [PATCH 11/15] cxl/acpi: Extract the host's component register
 base address from RCRB

On 01.09.22 12:00:03, Jonathan Cameron wrote:
> On Thu, 1 Sep 2022 09:38:13 +0200
> Robert Richter <rrichter@....com> wrote:
> 
> > On 31.08.22 12:56:56, Jonathan Cameron wrote:
> > > On Wed, 31 Aug 2022 10:15:59 +0200
> > > Robert Richter <rrichter@....com> wrote:  
> > 
> > > A few comments inline.  Mostly requests for references for things
> > > I couldn't find in the specs.  
> > 
> > Most of it comes from the pci base spec (5 or 6).
> 
> Ok. Extra references appreciated - these specs are huge, so saving
> searching time always good!

I will add comments for all ther refs in this patch.

[...]

> > > > +	cxl_probe_component_regs(parent, base, &comp_map);
> > > > +	iounmap(base);
> > > > +
> > > > +	if (!comp_map.hdm_decoder.valid) {
> > > > +		dev_err(parent, "HDM decoder registers not found\n");
> > > > +		return -ENXIO;  
> > > 
> > > Hmm. HDM decoder capability is optional for RCDs - might be using the
> > > range registers.  Seems like we'd really want to handle that for
> > > RCDs.  Future work I guess.  
> > 
> > I used the same message as for the non-RCD code path. HDM decoding is
> > just a subset of features handled with component regs. We need to
> > generalize the code for this in the future.
> 
> Sure - much more likely to need that generalized code for an RCD.
> IIRC a CXL 2.0 device must implement HDM decoders, even though the
> other path can be used by software that doesn't understand CXL 2.0.
> Our RCD might be because the device is CXL 1.1...

Yes, this will be a follow on series.

Thanks,

-Robert