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Subject: Re: [PATCH v2 1/2] PCI: Add support for a functional level reset
 based on _RST method
To:     Alex Williamson <alex.williamson@redhat.com>
CC:     Bjorn Helgaas <bhelgaas@google.com>, <linux-pci@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, Sinan Kaya <okaya@kernel.org>,
        Vikram Sethi <vsethi@nvidia.com>
References: <20210427022802.21458-1-sdonthineni@nvidia.com>
From:   Shanker R Donthineni <sdonthineni@nvidia.com>
Message-ID: <1cc3cad6-c100-5fe7-6fa2-664108c985e2@nvidia.com>
Date:   Tue, 27 Apr 2021 09:55:02 -0500
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Typo in the commit text  will post v3.

On 4/26/21 9:28 PM, Shanker Donthineni wrote:
> The _RST is a standard method specified in the ACPI specification. It
> provides a function level reset when it is described in the acpi_device
> context associated with PCI-device.
>
> Implement a new reset function pci_dev_acpi_reset() for probing RST
> method and execute if it is defined in the firmware.
>
> The ACPI based reset is called after the device-specific reset and
> before standard PCI hardware resets.
>
> Signed-off-by: Shanker Donthineni <sdonthineni@nvidia.com>
> ---
>  drivers/pci/pci.c | 35 +++++++++++++++++++++++++++++++++++
>  1 file changed, 35 insertions(+)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 16a17215f633..6dadb19848c2 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -5054,6 +5054,35 @@ static void pci_dev_restore(struct pci_dev *dev)
>  		err_handler->reset_done(dev);
>  }
>  
> +/**
> + * pci_dev_acpi_reset - do a function level reset using _RST method
> + * @dev: device to reset
> + * @probe: check if _RST method is included in the acpi_device context.
> + */
> +static int pci_dev_acpi_reset(struct pci_dev *dev, int probe)
> +{
> +#ifdef CONFIG_ACPI
> +	acpi_handle handle = ACPI_HANDLE(&dev->dev);
> +
> +	/* Return -ENOTTY if _RST method is not included in the dev context */
> +	if (!handle || !acpi_has_method(handle, "_RST"))
> +		return -ENOTTY;
> +
> +	/* Return 0 for probe phase indicating that we can reset this device */
> +	if (probe)
> +		return 0;
> +
> +	/* Invoke _RST() method to perform a function level reset */
> +	if (ACPI_FAILURE(acpi_evaluate_object(handle, "_RST", NULL, NULL))) {
> +		pci_warn(dev, "Failed to reset the device\n");
> +		return -EINVAL;
> +	}
> +	return 0;
> +#else
> +	return -ENOTTY;
> +#endif
> +}
> +
>  /**
>   * __pci_reset_function_locked - reset a PCI device function while holding
>   * the @dev mutex lock.
> @@ -5089,6 +5118,9 @@ int __pci_reset_function_locked(struct pci_dev *dev)
>  	 * reset mechanisms might be broken on the device.
>  	 */
>  	rc = pci_dev_specific_reset(dev, 0);
> +	if (rc != -ENOTTY)
> +		return rc;
> +	rc = pci_dev_acpi_reset(dev, 0);
>  	if (rc != -ENOTTY)
>  		return rc;
>  	if (pcie_has_flr(dev)) {
> @@ -5127,6 +5159,9 @@ int pci_probe_reset_function(struct pci_dev *dev)
>  	might_sleep();
>  
>  	rc = pci_dev_specific_reset(dev, 1);
> +	if (rc != -ENOTTY)
> +		return rc;
> +	rc = pci_dev_acpi_reset(dev, 1);
>  	if (rc != -ENOTTY)
>  		return rc;
>  	if (pcie_has_flr(dev))