linux-kernel - Re: [PATCH 05/14] cxl/mem: Register CXL memX devices

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Message-ID: <4d62a125-91e1-d32-66d3-1216d751f9b8@google.com>
Date:   Mon, 1 Feb 2021 13:53:03 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Ben Widawsky <ben.widawsky@...el.com>
cc:     linux-cxl@...r.kernel.org, Dan Williams <dan.j.williams@...el.com>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-pci@...r.kernel.org,
        Bjorn Helgaas <helgaas@...nel.org>,
        Chris Browy <cbrowy@...ry-design.com>,
        Christoph Hellwig <hch@...radead.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Jon Masters <jcm@...masters.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Vishal Verma <vishal.l.verma@...el.com>,
        daniel.lll@...baba-inc.com,
        "John Groves (jgroves)" <jgroves@...ron.com>,
        "Kelley, Sean V" <sean.v.kelley@...el.com>
Subject: Re: [PATCH 05/14] cxl/mem: Register CXL memX devices

On Mon, 1 Feb 2021, Ben Widawsky wrote:

> > > diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> > > new file mode 100644
> > > index 000000000000..fe7b87eba988
> > > --- /dev/null
> > > +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> > > @@ -0,0 +1,26 @@
> > > +What:		/sys/bus/cxl/devices/memX/firmware_version
> > > +Date:		December, 2020
> > > +KernelVersion:	v5.12
> > > +Contact:	linux-cxl@...r.kernel.org
> > > +Description:
> > > +		(RO) "FW Revision" string as reported by the Identify
> > > +		Memory Device Output Payload in the CXL-2.0
> > > +		specification.
> > > +
> > > +What:		/sys/bus/cxl/devices/memX/ram/size
> > > +Date:		December, 2020
> > > +KernelVersion:	v5.12
> > > +Contact:	linux-cxl@...r.kernel.org
> > > +Description:
> > > +		(RO) "Volatile Only Capacity" as reported by the
> > > +		Identify Memory Device Output Payload in the CXL-2.0
> > > +		specification.
> > > +
> > > +What:		/sys/bus/cxl/devices/memX/pmem/size
> > > +Date:		December, 2020
> > > +KernelVersion:	v5.12
> > > +Contact:	linux-cxl@...r.kernel.org
> > > +Description:
> > > +		(RO) "Persistent Only Capacity" as reported by the
> > > +		Identify Memory Device Output Payload in the CXL-2.0
> > > +		specification.
> > 
> > Aren't volatile and persistent capacities expressed in multiples of 256MB?
> 
> As of the spec today, volatile and persistent capacities are required to be
> in multiples of 256MB, however, future specs may not have such a requirement and
> I think keeping sysfs ABI easily forward portable makes sense.
> 

Makes sense, can we add that these are expressed in bytes or is that 
already implied?