linux-kernel - Re: [RFC PATCH] resource: Fix CXL node not populated issue

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Message-ID: <d8d2c310-2021-431f-adbe-71ad0a17896a@amd.com>
Date: Wed, 11 Dec 2024 22:17:11 +0530
From: Bharata B Rao <bharata@....com>
To: Dan Williams <dan.j.williams@...el.com>,
 Raghavendra K T <raghavendra.kt@....com>, linux-kernel@...r.kernel.org,
 linux-cxl@...r.kernel.org
Cc: Huang Ying <ying.huang@...el.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 David Hildenbrand <david@...hat.com>, Davidlohr Bueso <dave@...olabs.net>,
 Jonathan Cameron <jonathan.cameron@...wei.com>,
 Dave Jiang <dave.jiang@...el.com>,
 Alison Schofield <alison.schofield@...el.com>,
 Vishal Verma <vishal.l.verma@...el.com>, Ira Weiny <ira.weiny@...el.com>,
 Alistair Popple <apopple@...dia.com>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Bjorn Helgaas <bhelgaas@...gle.com>, Baoquan He <bhe@...hat.com>,
 ilpo.jarvinen@...ux.intel.com,
 Mika Westerberg <mika.westerberg@...ux.intel.com>,
 Fontenot Nathan <Nathan.Fontenot@....com>, Wei Huang <wei.huang2@....com>,
 regressions@...ts.linux.dev
Subject: Re: [RFC PATCH] resource: Fix CXL node not populated issue

On 11-Dec-24 2:08 PM, Dan Williams wrote:
> Ah, thanks for that!
> 
> So, it turns out Ying's patch is working as advertised. It is traversing
> past the top-level entry of the the iomem_resource topology to discover that a
> Soft Reserved range is described by CXL. Then the expectation is that
> the CXL subsystem parses the topology and registers a dax device.
> 
> I missed that detail in my repro because I was not testing the HMEM
> handoff.
> 
> Now, the dmesg shows that the CXL subsystem gives up early on the
> CXL devices as they do not appear to be meeting the expecations of a "CXL
> Memory Device" as described by the "PCI Header - Class Code Register
> (Offset 09h)" of the CXL spec.
> 
> Specifically these messages:
> 
>      [    4.449072] cxl_pci 0000:9f:00.0: registers not found: status mbox memdev
> 
> I think this situation is increasingly showing that the pace of
> non-standard quirks being deployed is higher than CXL subsystem is able
> to keep pace.
> 
> The immediate workaround to this problem that Linux discovered is to
> disable the cxl_acpi driver. Can you confirm that preventing the
> cxl_acpi driver from loading restores that missing node?

Yes, disabling CONFIG_CXL_ACPI gets the CXL node up with the memory. 
Thanks for this workaround.

> 
> Longer term the urgency of Nathan's patch [1] needs to be escalated.
> 
> [1]: http://lore.kernel.org/20241202155542.22111-1-nathan.fontenot@amd.com

I didn't find that patch helping though with CONFIG_CXL_ACPI kept enabled.

Regards,
Bharata.