Re: [PATCH v4 03/11] PCI/ACPI: Add PERST# Assertion Delay _DSM method

["Rafael J. Wysocki" <rafael@kernel.org>]

On Thu, May 29, 2025 at 11:57 PM Sathyanarayanan Kuppuswamy
<sathyanarayanan.kuppuswamy@linux.intel.com> wrote:
>
>
> On 5/29/25 4:16 AM, Badal Nilawar wrote:
> > From: Anshuman Gupta <anshuman.gupta@intel.com>
> >
> > Implement _DSM Method 0Bh as per PCI firmware specs
> > section 4.6.11 Rev 3.3.
> >
> > Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
> > Signed-off-by: Badal Nilawar <badal.nilawar@intel.com>
> > ---
> >   drivers/pci/pci-acpi.c   | 57 ++++++++++++++++++++++++++++++++++++++++
> >   include/linux/pci-acpi.h |  8 +++++-
> >   2 files changed, 64 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
> > index d33efba4ca94..88044491feaa 100644
> > --- a/drivers/pci/pci-acpi.c
> > +++ b/drivers/pci/pci-acpi.c
> > @@ -1531,6 +1531,63 @@ int pci_acpi_request_d3cold_aux_power(struct pci_dev *dev, u32 requested_power,
> >   }
> >   EXPORT_SYMBOL_GPL(pci_acpi_request_d3cold_aux_power);
> >
> > +/**
> > + * pci_acpi_add_perst_assertion_delay - Request PERST# delay via ACPI DSM
> > + * @dev: PCI device instance
> > + * @delay_us: Requested delay_us
> > + *
> > + * This function sends a request to the host BIOS via ACPI _DSM to grant the
> > + * required PERST# delay for the specified PCI device. It evaluates the _DSM
> > + * to request the PERST# delay and handles the response accordingly.
> > + *
> > + * Return: returns 0 on success and errno on failure.
> > + */
> > +int pci_acpi_add_perst_assertion_delay(struct pci_dev *dev, u32 delay_us)
> > +{
> > +     union acpi_object in_obj = {
> > +             .integer.type = ACPI_TYPE_INTEGER,
> > +             .integer.value = delay_us,
> > +     };
> > +
> > +     union acpi_object *out_obj;
> > +     acpi_handle handle;
> > +     int result, ret = -EINVAL;
> > +
> > +     if (!dev)
> > +             return -EINVAL;
> > +
> > +     handle = ACPI_HANDLE(&dev->dev);
> > +     if (!handle)
> > +             return -EINVAL;
> > +
> > +     if (!acpi_check_dsm(handle, &pci_acpi_dsm_guid, 4, 1 << DSM_PCI_PERST_ASSERTION_DELAY)) {
> > +             pci_dbg(dev, "ACPI _DSM 0%Xh not supported\n", DSM_PCI_PERST_ASSERTION_DELAY);
> > +             return -ENODEV;
> > +     }
> > +
> > +     out_obj = acpi_evaluate_dsm_typed(handle, &pci_acpi_dsm_guid, 4,
> > +                                       DSM_PCI_PERST_ASSERTION_DELAY,
> > +                                       &in_obj, ACPI_TYPE_INTEGER);
> > +     if (!out_obj)
> > +             return -EINVAL;
> > +
> > +     result = out_obj->integer.value;
> > +
> > +     if (result == delay_us) {
> > +             pci_info(dev, "PERST# Assertion Delay set to %u microseconds\n", delay_us);
> > +             ret = 0;
>
> I think above is a debug message. If it is set properly, why would you want to know
> the details?
>
> > +     } else if (result == 0) {
> > +             pci_warn(dev, "PERST# Assertion Delay request failed, no previous valid request\n");
> > +     } else {
> > +             pci_warn(dev, "PERST# Assertion Delay request failed, Previous valid delay: %u microseconds\n",
> > +                      result);
> > +     }
>
> May be you don't need to elaborate the error details. Will following work?
>
> pci_warn(dev, "PERST# Assertion Delay request failed, result:%u micro seconds\n", result);

Or even

pci_info(dev, "PERST# Assertion Delay request failed, using %u ms
delay\n", result);

And it doesn't really need to be pci_warn().

>
> > +
> > +     ACPI_FREE(out_obj);
> > +     return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(pci_acpi_add_perst_assertion_delay);
> > +
> >   static void pci_acpi_set_external_facing(struct pci_dev *dev)
> >   {
> >       u8 val;
> > diff --git a/include/linux/pci-acpi.h b/include/linux/pci-acpi.h
> > index 6079306ad754..e53d4893cf56 100644
> > --- a/include/linux/pci-acpi.h
> > +++ b/include/linux/pci-acpi.h
> > @@ -122,6 +122,7 @@ extern const guid_t pci_acpi_dsm_guid;
> >   #define DSM_PCI_POWER_ON_RESET_DELAY                0x08
> >   #define DSM_PCI_DEVICE_READINESS_DURATIONS  0x09
> >   #define DSM_PCI_D3COLD_AUX_POWER_LIMIT              0x0A
> > +#define DSM_PCI_PERST_ASSERTION_DELAY                0x0B
> >
> >   #ifdef CONFIG_PCIE_EDR
> >   void pci_acpi_add_edr_notifier(struct pci_dev *pdev);
> > @@ -135,7 +136,7 @@ int pci_acpi_set_companion_lookup_hook(struct acpi_device *(*func)(struct pci_de
> >   void pci_acpi_clear_companion_lookup_hook(void);
> >   int pci_acpi_request_d3cold_aux_power(struct pci_dev *dev, u32 requested_power,
> >                                     u32 *retry_interval);
> > -
> > +int pci_acpi_add_perst_assertion_delay(struct pci_dev *dev, u32 delay_us);
> >   #else       /* CONFIG_ACPI */
> >   static inline void acpi_pci_add_bus(struct pci_bus *bus) { }
> >   static inline void acpi_pci_remove_bus(struct pci_bus *bus) { }
> > @@ -144,6 +145,11 @@ static inline int pci_acpi_request_d3cold_aux_power(struct pci_dev *dev, u32 req
> >   {
> >       return -EOPNOTSUPP;
> >   }
> > +
> > +static inline int pci_acpi_add_perst_assertion_delay(struct pci_dev *dev, u32 delay_us)
> > +{
> > +     return -EOPNOTSUPP;
> > +}
> >   #endif      /* CONFIG_ACPI */
> >
> >   #endif      /* _PCI_ACPI_H_ */
>
> --
> Sathyanarayanan Kuppuswamy
> Linux Kernel Developer
>