Re: [PATCH 02/12] PCI/ACPI: Add PERST# Assertion Delay _DSM method

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Apr 01, 2025 at 09:02:15PM +0530, Anshuman Gupta wrote:
> Implement _DSM Method 11 as per PCI firmware specs
> section 4.6.11 Rev 3.3.

"PCI Firmware r3.3, sec 4.6.11" so the citation is major to minor.

"0xb" or "0Bh" to match spec usage.

> Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
> ---
>  drivers/pci/pci-acpi.c   | 53 ++++++++++++++++++++++++++++++++++++++++
>  include/linux/pci-acpi.h |  7 ++++++
>  2 files changed, 60 insertions(+)
> 
> diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
> index ebd49e43457e..04149f037664 100644
> --- a/drivers/pci/pci-acpi.c
> +++ b/drivers/pci/pci-acpi.c
> @@ -1499,6 +1499,59 @@ int pci_acpi_request_d3cold_aux_power(struct pci_dev *dev, u32 requested_power)
>  }
>  EXPORT_SYMBOL(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 || !ACPI_HANDLE(&dev->dev))
> +		return -EINVAL;
> +
> +	handle = ACPI_HANDLE(&dev->dev);

acpi_check_dsm().

> +	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) {
> +		dev_info(&dev->dev, "PERST# Assertion Delay set to"
> +			 "%u microseconds\n", delay_us);

pci_info().

Join these into a single string, even though they won't fit in a line
without wrapping.  This is to make them easier to grep for when a user
reports seeing the message.  (Do this on the previous patch too, where
I forgot to mention it.)

> +		ret = 0;
> +	} else if (result == 0) {
> +		dev_warn(&dev->dev, "PERST# Assertion Delay request failed,"
> +			 "no previous valid request\n");
> +	} else {
> +		dev_warn(&dev->dev,
> +			 "PERST# Assertion Delay request failed"
> +			 "Previous valid delay: %u microseconds\n", result);
> +	}
> +
> +	ACPI_FREE(out_obj);
> +	return ret;
> +}
> +EXPORT_SYMBOL(pci_acpi_add_perst_assertion_delay);