Re: [PATCH] PCI: dwc: Add the sysfs property to provide the LTSSM status of the PCIe link

[Hans Zhang]

On 2025/1/24 00:49, Bjorn Helgaas wrote:
> On Thu, Jan 23, 2025 at 03:13:26PM +0800, Hans Zhang wrote:
> > Add the sysfs property to provide a view of the current link's LTSSM
> > status from the root port device.
> >
> >    /sys/bus/pci/devices/<dev>/ltssm_status
>
> Would need a rationale, i.e., what benefit this provides.  Obviously
> this is currently only implemented for DWC-based controllers and
> probably not ever available for ACPI or other generic host bridges.
>
> Also documentation somewhere in
> Documentation/ABI/testing/sysfs-bus-pci*.
>
> LTSSM is applicable to all Downstream Ports, including both Root Ports
> and Switch Downstream Ports, but in general I doubt this information
> is available for Switches in any generic way.
>
> > +++ b/drivers/pci/pci-sysfs.c
> > @@ -1696,6 +1696,9 @@ const struct attribute_group *pci_dev_attr_groups[] = {
> >   #endif
> >   #ifdef CONFIG_PCIEASPM
> >   	&aspm_ctrl_attr_group,
> > +#endif
> > +#ifdef CONFIG_PCIE_DW_HOST
> > +	&dw_ltssm_status_attr_group,
> >   #endif
>
> I'm not convinced of the value of potentially dozens of device- or
> vendor-specific additions like this.


At present, someone has submitted the dwc common debugfs driver.

dwc common driver: add debugfs
https://lore.kernel.org/linux-pci/20250121111421.35437-3-shradha.t@xxxxxxxxxxx/


I will make a patch version based on this patch.

Best regards
Hans