Re: [PATCH v15 5/9] PCI: Allow userspace to query and set device reset mechanism

[Raphael Norwitz <raphael.norwitz@nutanix.com>]

On Thu, Aug 05, 2021 at 09:59:13PM +0530, Amey Narkhede wrote:
> Add reset_method sysfs attribute to enable user to query and set user
> preferred device reset methods and their ordering.
> 
> Co-developed-by: Alex Williamson <alex.williamson@redhat.com>
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> Signed-off-by: Amey Narkhede <ameynarkhede03@gmail.com>

Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>

> ---
>  Documentation/ABI/testing/sysfs-bus-pci |  19 ++++
>  drivers/pci/pci-sysfs.c                 |   1 +
>  drivers/pci/pci.c                       | 117 ++++++++++++++++++++++++
>  drivers/pci/pci.h                       |   2 +
>  4 files changed, 139 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
> index ef00fada2efb..ef66b62bf025 100644
> --- a/Documentation/ABI/testing/sysfs-bus-pci
> +++ b/Documentation/ABI/testing/sysfs-bus-pci
> @@ -121,6 +121,25 @@ Description:
>  		child buses, and re-discover devices removed earlier
>  		from this part of the device tree.
> 
> +What:		/sys/bus/pci/devices/.../reset_method
> +Date:		March 2021
> +Contact:	Amey Narkhede <ameynarkhede03@gmail.com>
> +Description:
> +		Some devices allow an individual function to be reset
> +		without affecting other functions in the same slot.
> +
> +		For devices that have this support, a file named
> +		reset_method will be present in sysfs. Initially reading
> +		this file will give names of the device supported reset
> +		methods and their ordering. After write, this file will
> +		give names and ordering of currently enabled reset methods.
> +		Writing the name or space separated list of names of any of
> +		the device supported reset methods to this file will set
> +		the reset methods and their ordering to be used when
> +		resetting the device. Writing empty string to this file
> +		will disable ability to reset the device and writing
> +		"default" will return to the original value.
> +
>  What:		/sys/bus/pci/devices/.../reset
>  Date:		July 2009
>  Contact:	Michael S. Tsirkin <mst@redhat.com>
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 316f70c3e3b4..54ee7193b463 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -1491,6 +1491,7 @@ const struct attribute_group *pci_dev_groups[] = {
>  	&pci_dev_config_attr_group,
>  	&pci_dev_rom_attr_group,
>  	&pci_dev_reset_attr_group,
> +	&pci_dev_reset_method_attr_group,
>  	&pci_dev_vpd_attr_group,
>  #ifdef CONFIG_DMI
>  	&pci_dev_smbios_attr_group,
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 8a516e9ca316..53d73770881f 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -5132,6 +5132,123 @@ static const struct pci_reset_fn_method pci_reset_fn_methods[] = {
>  	{ pci_reset_bus_function, .name = "bus" },
>  };
> 
> +static ssize_t reset_method_show(struct device *dev,
> +				 struct device_attribute *attr, char *buf)
> +{
> +	struct pci_dev *pdev = to_pci_dev(dev);
> +	ssize_t len = 0;
> +	int i, m;
> +
> +	for (i = 0; i < PCI_NUM_RESET_METHODS; i++) {
> +		m = pdev->reset_methods[i];
> +		if (!m)
> +			break;
> +
> +		len += sysfs_emit_at(buf, len, "%s%s", len ? " " : "",
> +				     pci_reset_fn_methods[m].name);
> +	}
> +
> +	if (len)
> +		len += sysfs_emit_at(buf, len, "\n");
> +
> +	return len;
> +}
> +
> +static ssize_t reset_method_store(struct device *dev,
> +				  struct device_attribute *attr,
> +				  const char *buf, size_t count)
> +{
> +	struct pci_dev *pdev = to_pci_dev(dev);
> +	int i, m = 0, n = 0;
> +	char *name, *options;
> +
> +	if (count >= (PAGE_SIZE - 1))
> +		return -EINVAL;
> +
> +	if (sysfs_streq(buf, "")) {
> +		goto exit;
> +	}
> +
> +	if (sysfs_streq(buf, "default")) {
> +		pci_init_reset_methods(pdev);
> +		return count;
> +	}
> +
> +	options = kstrndup(buf, count, GFP_KERNEL);
> +	if (!options)
> +		return -ENOMEM;
> +
> +	while ((name = strsep(&options, " ")) != NULL) {
> +		if (sysfs_streq(name, ""))
> +			continue;
> +
> +		name = strim(name);
> +
> +		for (m = 1; m < PCI_NUM_RESET_METHODS; m++) {
> +			if (sysfs_streq(name, pci_reset_fn_methods[m].name))
> +				break;
> +		}
> +
> +		if (m == PCI_NUM_RESET_METHODS) {
> +			pci_warn(pdev, "Skip invalid reset method '%s'", name);
> +			continue;
> +		}
> +
> +		for (i = 0; i < n; i++) {
> +			if (pdev->reset_methods[i] == m)
> +				break;
> +		}
> +
> +		if (i < n)
> +			continue;
> +
> +		if (pci_reset_fn_methods[m].reset_fn(pdev, 1)) {
> +			pci_warn(pdev, "Unsupported reset method '%s'", name);
> +			continue;
> +		}
> +
> +		pdev->reset_methods[n++] = m;
> +		BUG_ON(n == PCI_NUM_RESET_METHODS);
> +	}
> +
> +	kfree(options);
> +
> +exit:
> +	/* All the reset methods are invalid */
> +	if (n == 0 && m == PCI_NUM_RESET_METHODS)
> +		return -EINVAL;
> +	pdev->reset_methods[n] = 0;
> +	if (pdev->reset_methods[0] == 0) {
> +		pci_warn(pdev, "All device reset methods disabled by user");
> +	} else if ((pdev->reset_methods[0] != 1) &&
> +		   !pci_reset_fn_methods[1].reset_fn(pdev, 1)) {
> +		pci_warn(pdev, "Device specific reset disabled/de-prioritized by user");
> +	}
> +	return count;
> +}
> +static DEVICE_ATTR_RW(reset_method);
> +
> +static struct attribute *pci_dev_reset_method_attrs[] = {
> +	&dev_attr_reset_method.attr,
> +	NULL,
> +};
> +
> +static umode_t pci_dev_reset_method_attr_is_visible(struct kobject *kobj,
> +						    struct attribute *a, int n)
> +{
> +	struct pci_dev *pdev = to_pci_dev(kobj_to_dev(kobj));
> +
> +	if (!pci_reset_supported(pdev))
> +		return 0;
> +
> +	return a->mode;
> +}
> +
> +const struct attribute_group pci_dev_reset_method_attr_group = {
> +	.attrs = pci_dev_reset_method_attrs,
> +	.is_visible = pci_dev_reset_method_attr_is_visible,
> +};
> +
>  /**
>   * __pci_reset_function_locked - reset a PCI device function while holding
>   * the @dev mutex lock.
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 7438953745e0..31458d48eda7 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -714,4 +714,6 @@ static inline int pci_acpi_program_hp_params(struct pci_dev *dev)
>  extern const struct attribute_group aspm_ctrl_attr_group;
>  #endif
> 
> +extern const struct attribute_group pci_dev_reset_method_attr_group;
> +
>  #endif /* DRIVERS_PCI_H */
> --
> 2.32.0
>