linux-kernel - Re: [PATCH v1 1/2] cxl_test: enable zero sized decoders under hb0

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Message-ID: <aPXgLp1Em6wKlx0t@aschofie-mobl2.lan>
Date: Mon, 20 Oct 2025 00:09:34 -0700
From: Alison Schofield <alison.schofield@...el.com>
To: Vishal Aslot <vaslot@...dia.com>
CC: Davidlohr Bueso <dave@...olabs.net>, Jonathan Cameron
	<jonathan.cameron@...wei.com>, Dave Jiang <dave.jiang@...el.com>, "Vishal
 Verma" <vishal.l.verma@...el.com>, Ira Weiny <ira.weiny@...el.com>, "Dan
 Williams" <dan.j.williams@...el.com>, Li Ming <ming.li@...omail.com>, "Peter
 Zijlstra" <peterz@...radead.org>, "open list:COMPUTE EXPRESS LINK (CXL)"
	<linux-cxl@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 1/2] cxl_test: enable zero sized decoders under hb0

On Tue, Oct 14, 2025 at 07:40:05PM -0700, Vishal Aslot wrote:
> The cxl core in linux updated to supported committed
> decoders of zero size, because this is allowed by
> the CXL spec.

Tell more about what the spec allows?

> 
> This patch updates cxl_test to enable decoders 1 and 2
> in the host-bridge 0 port, in a switch uport under hb0,
> and the endpoints ports with size zero simulating
> committed zero sized decoders.

Decoders 1 & 2 - those are after decoder 0, the autoregion.
That's a problem ATM, when we try to teardown the autoregion we
get out of order resets. Like I asked in the other patch, if there
are rules about where these zero size decoders may appear, that
may make the solution here simpler.

Add the skip to mock_devm_enumerate_decoders() to clean up -
a bunch like this:
[   94.222456] cxl decoder0.0: unsupported mode 223426864
that were followed by construct region failures...
[   94.222456] cxl decoder0.0: unsupported mode 223426864
[   94.223790] probe of endpoint13 returned 0 after 136794 usecs
[   94.224595] cxl_mock_mem cxl_mem.6: mem3:decoder15.1: construct_region failed assign region: -22

FWIW - cxl-test mocks the init, enumerate, commit, and reset of the
decoders, so all those need to be coordinated w the 'real' driver.
That may sound like a pain and it could lead to bugs that are only
in cxl-test - but it lets us then test region creation paths.

-- Alison