Re: [PATCH V2] PCI: Hide SBR from reset_methods if masked by CXL

[Jonathan Cameron]

On Wed, 25 Feb 2026 09:34:00 -0700
Dave Jiang <dave.jiang@xxxxxxxxx> wrote:

> On 2/25/26 6:38 AM, Vidya Sagar wrote:
> > The CXL specification (e.g., CXL r3.1 v1.0, sec 8.1.5.2) defines
> > the "Unmask SBR" bit in the Port Control Extensions Register.
> > When this bit is 0 (default), asserting the Secondary Bus Reset (SBR) bit
> > in the Bridge Control register has no effect on the downstream bus.
> > 
> > Currently, the Linux PCI core checks this condition in
> > pci_reset_bus_function(). If SBR is masked, it returns -ENOTTY during the
> > execution of the reset. However, during the probe phase (when probe=true),
> > the function currently returns 0. This 0 return value incorrectly signals
> > to the PCI subsystem that SBR is a viable reset method for the device.
> > 
> > As a result, 'bus' is listed in the device's
> > /sys/bus/pci/devices/.../reset_methods attribute, even though the hardware
> > is incapable of performing it. If a user attempts to write bus to reset
> > method or triggers a reset that falls back to SBR, the operation fails
> > with: "bash: echo: write error: Inappropriate ioctl for device" error.
> > 
> > This patch modifies pci_reset_bus_function() to return -ENOTTY immediately
> > if cxl_sbr_masked() is true, regardless of the probe argument. This
> > ensures that 'bus' is not advertised in reset_methods when the hardware
> > prevents it, improving clarity for users and aligning the sysfs capability
> > report with actual hardware behavior.
> > 
> > Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx>  
> 
> Reviewed-by: Dave Jiang <dave.jiang@xxxxxxxxx>
Reviewed-by: Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>