linux-kernel - Re: [RESEND v13 17/25] cxl: Introduce cxl_pci_drv

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Message-ID: <aQuOiK8S31w44pYR@gourry-fedora-PF4VCD3F>
Date: Wed, 5 Nov 2025 12:51:04 -0500
From: Gregory Price <gourry@...rry.net>
To: Terry Bowman <terry.bowman@....com>
Cc: dave@...olabs.net, jonathan.cameron@...wei.com, dave.jiang@...el.com,
	alison.schofield@...el.com, dan.j.williams@...el.com,
	bhelgaas@...gle.com, shiju.jose@...wei.com, ming.li@...omail.com,
	Smita.KoralahalliChannabasappa@....com, rrichter@....com,
	dan.carpenter@...aro.org, PradeepVineshReddy.Kodamati@....com,
	lukas@...ner.de, Benjamin.Cheatham@....com,
	sathyanarayanan.kuppuswamy@...ux.intel.com,
	linux-cxl@...r.kernel.org, alucerop@....com, ira.weiny@...el.com,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [RESEND v13 17/25] cxl: Introduce cxl_pci_drv_bound() to check
 for bound driver

On Tue, Nov 04, 2025 at 11:02:57AM -0600, Terry Bowman wrote:
> CXL devices handle protocol errors via driver-specific callbacks rather
> than the generic pci_driver::err_handlers by default. The callbacks are
> implemented in the cxl_pci driver and are not part of struct pci_driver, so
> cxl_core must verify that a device is actually bound to the cxl_pci
> module's driver before invoking the callbacks (the device could be bound
> to another driver, e.g. VFIO).
> 
> However, cxl_core can not reference symbols in the cxl_pci module because
> it creates a circular dependency. This prevents cxl_core from checking the
> EP's bound driver and calling the callbacks.
> 
> To fix this, move drivers/cxl/pci.c into drivers/cxl/core/pci_drv.c and
> build it as part of the cxl_core module. Compile into cxl_core using
> CXL_PCI and CXL_CORE Kconfig dependencies. This removes the standalone
> cxl_pci module, consolidates the cxl_pci driver code into cxl_core, and
> eliminates the circular dependency so cxl_core can safely perform
> bound-driver checks and invoke the CXL PCI callbacks.
> 
> Introduce cxl_pci_drv_bound() to return boolean depending on if the PCI EP
> parameter is bound to a CXL driver instance. This will be used in future
> patch when dequeuing work from the kfifo.
> 
> Signed-off-by: Terry Bowman <terry.bowman@....com>
> Reviewed-by: Dave Jiang <dave.jiang@...el.com>
> Reviewed-by: Ben Cheatham <benjamin.cheatham@....com>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>
> 
> ---

This commit causes my QEMU basic expander setup and a real device setup
to fail to probe the cxl_core driver.

[    2.697094] cxl_core 0000:0d:00.0: BAR 0 [mem 0xfe800000-0xfe80ffff 64bit]: not claimed; can't enable device
[    2.697098] cxl_core 0000:0d:00.0: probe with driver cxl_core failed with error -22

Probe order issue when CXL drivers are built-in maybe?

~Gregory