Re: [PATCH v3 01/11] PCI/ACPI: Add D3cold Aux Power Limit_DSM method

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

On 24-05-2025 11:30, Sathyanarayanan Kuppuswamy wrote:
>
> On 5/23/25 12:01 PM, Badal Nilawar 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.
>
> Add some info about why you are not adding this support?
Scope is limited to enable the use case of VRAM-SR on BMG GPU. I will 
mention this in cover letter.
>
>> One possible mitigation would be only allowing only first PCIe
>> Non-Bridge Endpoint Function 0 driver to call_DSM method 0Ah.
>>
>> V2(Bjorn/Rafael):
>>    - Call acpi_dsm_check() to find method 0Ah supported
>>    - Return retry interval to caller
>>
>> Signed-off-by: Varun Gupta<varun.gupta@intel.com>
>> Signed-off-by: Badal Nilawar<badal.nilawar@intel.com>
>> Signed-off-by: Anshuman Gupta<anshuman.gupta@intel.com>
>> ---
>>   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..76b19525535f 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)
>> +        return -EINVAL;
>
> Is retry_interval param optional? If not may be a check here for non 
> NULL condition is needed.
Yes its optional, its up to caller weather to retry or not.
>
>> +
>> +    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:
>> +        pci_dbg(dev, "D3cold Aux Power %u mW request denied\n",
>> +            requested_power);
>
> is this not a error?

No its not error. BIOS Firmware can deny the aux power request.

Regards,
Badal

>
>> +        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 (retry_interval) {
>> +                *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..1705d03bfe26 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 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_ */
>