Re: [RESEND v13 17/25] cxl: Introduce cxl_pci_drv_bound() to check for bound driver

Gregory Price
2025-11-05T17:51:07Z

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@amd.com>
> Reviewed-by: Dave Jiang <dave.jiang@intel.com>
> Reviewed-by: Ben Cheatham <benjamin.cheatham@amd.com>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.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