Re: [PATCH v6 02/17] PCI/CXL: Probe the underlying bus reset in cxl_reset_bus_function()

[Jonathan Cameron <jic23@kernel.org>]

On Wed, 23 Sep 2026 13:11:21 -0700
Nicolin Chen <nicolinc@nvidia.com> wrote:

> cxl_reset_bus_function() reports "supported" to a probe after checking only
> that the upstream bridge carries a CXL port DVSEC. The underlying bus reset
> can still be unavailable, e.g. on a bus shared with other devices, so both
> the reset_methods[] array and the reset_method sysfs node end up listing a
> "cxl_bus" that is guaranteed to fail with -ENOTTY when it is attempted.
> 
> Probe the underlying pci_dev_reset_slot_function() and then, if it is not
> applicable, pci_parent_bus_reset(). These are the same two checks that the
> actual reset runs, so a shared-bus CXL device no longer advertises a method
> that can never succeed.
> 
> Probing via pci_reset_bus_function() would not work: its cxl_sbr_masked()
> check rejects every CXL port with a masked SBR, while the do-reset path in
> this function unmasks the SBR before resetting. Such a port would wrongly
> probe as unsupported.
> 
> Move the port control register read above the probe branch as well, so that
> probe runs the same checks. That read asserts no reset, and a failure means
> the device cannot be reset this way, which is a probe-time answer.
> 
> Also pass an explicit PCI_RESET_DO_RESET at the do-reset call site, since
> probe is always false at that point.
> 
> Fixes: 53c49b6e6dd2e ("PCI/CXL: Add 'cxl_bus' reset method for devices below CXL Ports")
> Assisted-by: LLM
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Nice clear explanation and it looks like the code does what that says,
so I'm fine with this.

Reviewed-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>