linux-kernel - Re: [PATCH v5 0/7] Add managed SOFT RESERVE resource handling

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Message-ID: <6880fe9dbb6ec_e74a1004b@dwillia2-mobl4.notmuch>
Date: Wed, 23 Jul 2025 08:24:13 -0700
From: <dan.j.williams@...el.com>
To: "Koralahalli Channabasappa, Smita"
	<Smita.KoralahalliChannabasappa@....com>, Alison Schofield
	<alison.schofield@...el.com>
CC: <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
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	PradeepVineshReddy Kodamati <PradeepVineshReddy.Kodamati@....com>, Zhijian Li
	<lizhijian@...itsu.com>
Subject: Re: [PATCH v5 0/7] Add managed SOFT RESERVE resource handling

Koralahalli Channabasappa, Smita wrote:
[..]
> That said, I'm still evaluating better options to more robustly 
> coordinate probe ordering between cxl_acpi, cxl_port, cxl_mem and 
> cxl_region and looking for suggestions here.

I never quite understood the arguments around why
wait_for_device_probe() does not work, but I did find a bug in my prior
thinking on the way towards this RFC [1]. The misunderstanding was that
MODULE_SOFTDEP() only guarantees that the module gets loaded eventually,
but it does not guarantee that the softdep has completed init before the
caller performs its own init.

It works sometimes, and that is probably what misled me about that
contract. request_module() is synchronous. With that in place I now see
what wait_for_device_probe() does the right thing. It flushes cxl_pci
attach for devices present at boot, and all follow-on probe work gets
flushed as well.

With that in hand the RFC now has a stable quiesce point to walk the CXL
topology and make decisions. The RFC is effectively a fix for platforms
where CXL loses the MODULE_SOFTDEP() race.

[1]: http://lore.kernel.org/68808fb4e4cbf_137e6b100cc@dwillia2-xfh.jf.intel.com.notmuch