Re: [PATCH v4 01/11] PCI/ACPI: Add D3cold Aux Power Limit_DSM method

["Nilawar, Badal" <badal.nilawar@intel.com>]

On 02-07-2025 16:38, Rafael J. Wysocki wrote:
> On Thu, May 29, 2025 at 1:14 PM Badal Nilawar <badal.nilawar@intel.com> wrote:
>> From: Anshuman Gupta <anshuman.gupta@intel.com>
>>
>> Implement _DSM method 0Ah according to PCI firmware specifications,
>> section 4.6.10 Rev 3.3., to request auxilary power needed for the
>> device when in D3Cold.
>>
>> Note that this implementation assumes only a single device below the
>> Downstream Port will request for Aux Power Limit under a given
>> Root Port because it does not track and aggregate requests
>> from all child devices below the Downstream Port as required
>> by Section 4.6.10 Rev 3.3.
>>
>> One possible mitigation would be only allowing only first PCIe
>> Non-Bridge Endpoint Function 0 driver to call_DSM method 0Ah.
>>
>> Signed-off-by: Varun Gupta <varun.gupta@intel.com>
> What's this S-o-b for?
>
>> Signed-off-by: Badal Nilawar <badal.nilawar@intel.com>
>> Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
>> ---
>> V2(Bjorn/Rafael):
>>    - Call acpi_dsm_check() to find method 0Ah supported
>>    - Return retry interval to caller
>> V3(Kuppuswamy)
>>    - Add NULL check for retry interval
>> ---
>>   drivers/pci/pci-acpi.c   | 87 ++++++++++++++++++++++++++++++++++++++++
>>   include/linux/pci-acpi.h |  8 ++++
>>   2 files changed, 95 insertions(+)
>>
>> diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
>> index af370628e583..87f30910a5f1 100644
>> --- a/drivers/pci/pci-acpi.c
>> +++ b/drivers/pci/pci-acpi.c
>> @@ -1421,6 +1421,93 @@ static void pci_acpi_optimize_delay(struct pci_dev *pdev,
>>          ACPI_FREE(obj);
>>   }
>>
>> +/**
>> + * pci_acpi_request_d3cold_aux_power - Request aux power while device is in D3Cold
>> + * @dev: PCI device instance
>> + * @requested_power: Requested auxiliary power in milliwatts
>> + * @retry_interval: Retry interval returned by platform to retry auxiliary
>> + *                  power request
>> + *
>> + * This function sends a request to the host BIOS via root port ACPI _DSM Function 0Ah
>> + * for the auxiliary power needed by the PCI device when it is in D3Cold.
>> + * It checks and evaluates the _DSM (Device Specific Method) to request the auxiliary
>> + * power and handles the response accordingly.
>> + *
>> + * This function shall be only called by 1st non-bridge Endpoint driver
>> + * on Function 0. For a Multi-Function Device, the driver for Function 0 is
>> + * required to report an aggregate power requirement covering all
>> + * functions contained within the device.
>> + *
>> + * Return: Returns 0 on success and errno on failure.
>> + */
>> +int pci_acpi_request_d3cold_aux_power(struct pci_dev *dev, u32 requested_power,
>> +                                     u32 *retry_interval)
>> +{
>> +       union acpi_object in_obj = {
>> +               .integer.type = ACPI_TYPE_INTEGER,
>> +               .integer.value = requested_power,
>> +       };
>> +
>> +       union acpi_object *out_obj;
>> +       acpi_handle handle;
>> +       int result, ret = -EINVAL;
>> +
>> +       if (!dev || !retry_interval)
>> +               return -EINVAL;
>> +
>> +       handle = ACPI_HANDLE(&dev->dev);
>> +       if (!handle)
>> +               return -EINVAL;
>> +
>> +       if (!acpi_check_dsm(handle, &pci_acpi_dsm_guid, 4, 1 << DSM_PCI_D3COLD_AUX_POWER_LIMIT)) {
>> +               pci_dbg(dev, "ACPI _DSM 0%Xh not supported\n", DSM_PCI_D3COLD_AUX_POWER_LIMIT);
>> +               return -ENODEV;
>> +       }
>> +
>> +       out_obj = acpi_evaluate_dsm_typed(handle, &pci_acpi_dsm_guid, 4,
>> +                                         DSM_PCI_D3COLD_AUX_POWER_LIMIT,
>> +                                         &in_obj, ACPI_TYPE_INTEGER);
>> +       if (!out_obj)
>> +               return -EINVAL;
>> +
>> +       result = out_obj->integer.value;
>> +       if (retry_interval)
>> +               *retry_interval = 0;
>> +
>> +       switch (result) {
>> +       case 0x0:
> It would be better to use an enum for the possible return values.

Sure I will use enum, something like

typedef enum {
     AUX_PWR_REQ_DENIED               = 0x0,
     AUX_PWR_REQ_GRANTED              = 0x1,
     AUX_PWR_REQ_NO_MAIN_PWR_REMOVAL  = 0x2
} AUX_PWR_REQ_STATUS;

>
>> +               pci_dbg(dev, "D3cold Aux Power %u mW request denied\n",
>> +                       requested_power);
>> +               break;
>> +       case 0x1:
>> +               pci_info(dev, "D3cold Aux Power request granted: %u mW\n",
>> +                        requested_power);
>> +               ret = 0;
>> +               break;
>> +       case 0x2:
>> +               pci_info(dev, "D3cold Aux Power: Main power won't be removed\n");
>> +               ret = -EBUSY;
>> +               break;
>> +       default:
>> +               if (result >= 0x11 && result <= 0x1F) {
> if (!(result & ~0x1F))

This will pick result = 0x10 as well, that's why checking the range 0x11 
- 0x1F.

> I think, and it would be better to use a symbol for this mask (and below too).
I will add an enum for the retry interval range — something like 
AUX_PWR_REQ_RETRY_INT_MIN and AUX_PWR_REQ_RETRY_INT_MAX for 0x11 and 0x1F.

>
>> +                       if (retry_interval) {
> This has been checked already and is guaranteed to be nonzero at this point.

Sure.

Thanks,
Badal

>
>> +                               *retry_interval = result & 0xF;
>> +                               pci_warn(dev, "D3cold Aux Power request needs retry interval: %u seconds\n",
>> +                                        *retry_interval);
>> +                               ret = -EAGAIN;
>> +                       }
>> +               } else {
>> +                       pci_err(dev, "D3cold Aux Power: Reserved or unsupported response: 0x%x\n",
>> +                               result);
>> +               }
>> +               break;
>> +       }
>> +
>> +       ACPI_FREE(out_obj);
>> +       return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(pci_acpi_request_d3cold_aux_power);
>> +
>>   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 078225b514d4..6079306ad754 100644
>> --- a/include/linux/pci-acpi.h
>> +++ b/include/linux/pci-acpi.h
>> @@ -121,6 +121,7 @@ extern const guid_t pci_acpi_dsm_guid;
>>   #define DSM_PCI_DEVICE_NAME                    0x07
>>   #define DSM_PCI_POWER_ON_RESET_DELAY           0x08
>>   #define DSM_PCI_DEVICE_READINESS_DURATIONS     0x09
>> +#define DSM_PCI_D3COLD_AUX_POWER_LIMIT         0x0A
>>
>>   #ifdef CONFIG_PCIE_EDR
>>   void pci_acpi_add_edr_notifier(struct pci_dev *pdev);
>> @@ -132,10 +133,17 @@ static inline void pci_acpi_remove_edr_notifier(struct pci_dev *pdev) { }
>>
>>   int pci_acpi_set_companion_lookup_hook(struct acpi_device *(*func)(struct pci_dev *));
>>   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);
>>
>>   #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) { }
>> +static inline int pci_acpi_request_d3cold_aux_power(struct pci_dev *dev, u32 requested_power,
>> +                                                   u32 *retry_interval)
>> +{
>> +       return -EOPNOTSUPP;
>> +}
>>   #endif /* CONFIG_ACPI */
>>
>>   #endif /* _PCI_ACPI_H_ */
>> --