Re: [PATCH v1 2/5] PCI/CXL: Probe the underlying bus reset in cxl_reset_bus_function()

[Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>]

On Tue, 3 Nov 2026 10:44:29 -0800
Nicolin Chen <nicolinc@nvidia.com> wrote:

> On Tue, Nov 03, 2026 at 10:33:43AM -0800, Nicolin Chen 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")
> > Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>  
> 
> Ah, I missed Jonathan's review tag during the split:
> https://lore.kernel.org/linux-iommu/20260926001311.7c4be583@jic23-hlaptop/
> 
> Jonathan, would you mind giving another review tag here? It's the
> exact same patch that you reviewed. Sorry for the inconvenience.
> 
Reviewed-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>

> Nicolin