linux-kernel - Re: [PATCH v9 00/19] DCD: Add support for Dynamic Capacity Devices (DCD)

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Message-ID: <67fde59784933_71fe2945a@dwillia2-xfh.jf.intel.com.notmuch>
Date: Mon, 14 Apr 2025 21:50:31 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>, Ira Weiny
	<ira.weiny@...el.com>
CC: Dave Jiang <dave.jiang@...el.com>, Fan Ni <fan.ni@...sung.com>, "Dan
 Williams" <dan.j.williams@...el.com>, Davidlohr Bueso <dave@...olabs.net>,
	Alison Schofield <alison.schofield@...el.com>, Vishal Verma
	<vishal.l.verma@...el.com>, <linux-cxl@...r.kernel.org>,
	<nvdimm@...ts.linux.dev>, <linux-kernel@...r.kernel.org>, Li Ming
	<ming.li@...omail.com>
Subject: Re: [PATCH v9 00/19] DCD: Add support for Dynamic Capacity Devices
 (DCD)

Jonathan Cameron wrote:
[..]
> To me we don't need to answer the question of whether we fully understand
> requirements, or whether this support covers them, but rather to ask
> if anyone has requirements that are not sensible to satisfy with additional
> work building on this?

Wearing only my upstream kernel development hat, the question for
merging is "what is the end user visible impact of merging this?". As
long as DCD remains in proof-of-concept mode then leave the code out of
tree until it is ready to graduate past that point.

Same held for HDM-D support which was an out-of-tree POC until
Alejandro arrived with the SFC consumer.

DCD is joined by HDM-DB (awaiting an endpoint) and CXL Error Isolation
(awaiting a production consumer) as solutions that have time to validate
that the ecosystem is indeed graduating to consume them. There was no
"chicken-egg" paradox for the ecosystem to deliver base
static-memory-expander CXL support.

The ongoing failure to get productive engagement on just how ruthlessly
simple the implementation could be and still meet planned usages
continues to give the impression that Linux is way out in front of
hardware here. Uncomfortably so.