Re: [PATCH 2/2] cxl/core: Recover from PM Init failure via cxl_reset_bus_function()

[Alison Schofield]

On Tue, Apr 28, 2026 at 08:24:35PM +0200, Fabio M. De Francesco wrote:
> CXL r4.0 sec 8.1.5.1 Implementation Note describes a scenario in which a
> Secondary Bus Reset, a Link Down, or Downstream Port Containment on a
> CXL Downstream Port prevents Port PM Init from completing when ACS
> Source Validation is enabled.
> 
> During CXL enumeration, for each CXL Downstream Port in a memdev's
> ancestry, check whether PM Init has completed. If it has not, invoke
> cxl_reset_bus_function() which is exported for use by CXL.

Hi Fabio, Not a full review yet, but that !! caught my eye, so...

> 
> Signed-off-by: Fabio M. De Francesco <fabio.m.de.francesco@xxxxxxxxxxxxxxx>
> ---
>  drivers/cxl/core/pci.c        | 30 ++++++++++++++++++++++++++++++
>  drivers/cxl/core/port.c       | 22 ++++++++++++++++++++++
>  drivers/cxl/cxlpci.h          |  3 +++
>  drivers/pci/pci.c             |  3 ++-
>  include/linux/pci.h           |  1 +
>  include/uapi/linux/pci_regs.h |  2 ++
>  6 files changed, 60 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
> index d1f487b3d809..de6a317df650 100644
> --- a/drivers/cxl/core/pci.c
> +++ b/drivers/cxl/core/pci.c
> @@ -926,3 +926,33 @@ int cxl_port_get_possible_dports(struct cxl_port *port)
>  
>  	return ctx.count;
>  }
> +
> +/**
> + * cxl_port_pm_init_is_complete - check the downstream port's PM Init Complete
> + * @pdev: downstream port
> + *
> + * Read the Port Power Management Initialization Complete bit in the
> + * Downstream Port's CXL DVSEC Port Extended Status register.
> + *
> + * Return: false only when the bit is observably clear. Return true when PM
> + * init is complete, when @pdev is not a CXL port (no Port DVSEC), or when
> + * the status register cannot be read.
> + */
> +bool cxl_port_pm_init_is_complete(struct pci_dev *pdev)
> +{
> +	u16 status;
> +	u16 dvsec;
> +	int rc;
> +
> +	dvsec = pci_find_dvsec_capability(pdev, PCI_VENDOR_ID_CXL,
> +					  PCI_DVSEC_CXL_PORT);
> +	if (!dvsec)
> +		return true;
> +
> +	rc = pci_read_config_word(pdev, dvsec + PCI_DVSEC_CXL_PORT_EXT_STATUS,
> +				  &status);
> +	if (rc || PCI_POSSIBLE_ERROR(status))
> +		return true;
> +
> +	return !!FIELD_GET(PCI_DVSEC_CXL_PORT_EXT_STATUS_PM_INIT_COMP, status);
> +}

The !! seems unnecessary here since this is already a single bit FIELD_GET(),
ie. result is 0 or 1.

I also wouldn't mind this being extra reader friendly like below,
but I'm happy if you just get rid of the !!

bool complete;

complete = FIELD_GET(....);

return complete;