Re: [PATCH v4 1/2] PCI: Add support for a function level reset based on _RST method

[Alex Williamson <alex.williamson@redhat.com>]

On Wed, 28 Apr 2021 19:49:06 -0500
Shanker Donthineni <sdonthineni@nvidia.com> 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 binding
> information is available only after calling device_add(), so move
> pci_init_reset_methods() to end of the pci_device_add().
> 
> The default priority of the acpi reset is set to below device-specific
> and above hardware resets.
> 
> Signed-off-by: Shanker Donthineni <sdonthineni@nvidia.com>
> ---
> changes since v2:
>  - fix typo in the commit text
> changes since v2:
>  - rebase patch on top of https://lore.kernel.org/linux-pci/20210409192324.30080-1-ameynarkhede03@gmail.com/
> 
>  drivers/pci/pci.c   | 30 ++++++++++++++++++++++++++++++
>  drivers/pci/probe.c |  2 +-
>  include/linux/pci.h |  2 +-
>  3 files changed, 32 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 664cf2d358d6..510f9224a3b0 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -5076,6 +5076,35 @@ 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
> +}
> +
>  /*
>   * The ordering for functions in pci_reset_fn_methods
>   * is required for reset_methods byte array defined
> @@ -5083,6 +5112,7 @@ static void pci_dev_restore(struct pci_dev *dev)
>   */
>  const struct pci_reset_fn_method pci_reset_fn_methods[] = {
>  	{ .reset_fn = &pci_dev_specific_reset, .name = "device_specific" },
> +	{ .reset_fn = &pci_dev_acpi_reset, .name = "acpi_reset" },

Would it make sense to name this "acpi_rst" after the method name?
Otherwise "_reset" is a bit redundant to the sysfs attribute, we could
simply name it "acpi" to indicate an ACPI based reset.  Thanks,

Alex


>  	{ .reset_fn = &pcie_reset_flr, .name = "flr" },
>  	{ .reset_fn = &pci_af_flr, .name = "af_flr" },
>  	{ .reset_fn = &pci_pm_reset, .name = "pm" },
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 4764e031a44b..d4becd6ffb52 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2403,7 +2403,6 @@ static void pci_init_capabilities(struct pci_dev *dev)
>  	pci_rcec_init(dev);		/* Root Complex Event Collector */
>  
>  	pcie_report_downtraining(dev);
> -	pci_init_reset_methods(dev);
>  }
>  
>  /*
> @@ -2494,6 +2493,7 @@ void pci_device_add(struct pci_dev *dev, struct pci_bus *bus)
>  	dev->match_driver = false;
>  	ret = device_add(&dev->dev);
>  	WARN_ON(ret < 0);
> +	pci_init_reset_methods(dev);
>  }
>  
>  struct pci_dev *pci_scan_single_device(struct pci_bus *bus, int devfn)
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 9f8347799634..b4a5d2146542 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -49,7 +49,7 @@
>  			       PCI_STATUS_SIG_TARGET_ABORT | \
>  			       PCI_STATUS_PARITY)
>  
> -#define PCI_RESET_FN_METHODS 5
> +#define PCI_RESET_FN_METHODS 6
>  
>  /*
>   * The PCI interface treats multi-function devices as independent