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

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

On 05-09-2025 00:14, Bjorn Helgaas wrote:
> On Thu, May 29, 2025 at 04:46:46PM +0530, 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.
> Update citation as for the other _DSM function.
Sure.
>
>> 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.
> Reword in imperative mood.
>
> Like pci_acpi_request_d3cold_aux_power(), I think the driver should
> call this with its device, not the Root Port.
Ok.
>
>> + * 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;
>> +	} 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);
>> +	}
>> +
>> +	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)
> Wrap to fit in 80 columns like the rest of the file.

Ok.

Thanks,
Badal

>> +{
>> +	return -EOPNOTSUPP;
>> +}
>>   #endif	/* CONFIG_ACPI */
>>   
>>   #endif	/* _PCI_ACPI_H_ */
>> -- 
>> 2.34.1
>>