by Shanker Donthineni

[permalink] [raw]

Subject: Re: [PATCH v13 5/9] PCI: Allow userspace to query and set device reset mechanism

On 8/1/21 9:25 AM, Amey Narkhede wrote:
> External email: Use caution opening links or attachments
>
>
> 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 <[email protected]>
> Signed-off-by: Alex Williamson <[email protected]>
> Signed-off-by: Amey Narkhede <[email protected]>
> ---
> Documentation/ABI/testing/sysfs-bus-pci | 19 +++++
> drivers/pci/pci-sysfs.c | 1 +
> drivers/pci/pci.c | 105 ++++++++++++++++++++++++
> drivers/pci/pci.h | 2 +
> 4 files changed, 127 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 <[email protected]>
> +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 <[email protected]>
> 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 932dd21e759b..c496cd164aca 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -5132,6 +5132,111 @@ 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 = 0;
> + char *name, *options = NULL;
> +
> + if (count >= (PAGE_SIZE - 1))
> + return -EINVAL;
> +
> + if (sysfs_streq(buf, "")) {
> + pdev->reset_methods[0] = 0;
> + pci_warn(pdev, "All device reset methods disabled by user");
> + return count;
> + }
> +
> + 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) {
> + int m;
> +
> + if (sysfs_streq(name, ""))
> + continue;
> +
> + name = strim(name);
> +
> + for (m = 1; m < PCI_NUM_RESET_METHODS && i < PCI_NUM_RESET_METHODS; m++) {
> + if (sysfs_streq(name, pci_reset_fn_methods[m].name) &&
> + !pci_reset_fn_methods[m].reset_fn(pdev, 1)) {
> + pdev->reset_methods[i++] = m;
> + break;
> + }
> + }
> +
Checking reset method logic isn't optimized, iterating through all entries if the
device doesn't support a requested method.

Something like this:
        for (m = 1; m < PCI_NUM_RESET_METHODS && i < PCI_NUM_RESET_METHODS; m++) {
                if (!sysfs_streq(name, pci_reset_fn_methods[m].name))
                        continue;
                if(!pci_reset_fn_methods[m].reset_fn(pdev, 1))
                        pdev->reset_methods[i++] = m;
                break;
        }

I think we should avoid duplicate entries in pdev->reset_methods.
Example:
   root# cat reset_method
   acpi flr bus

   root# echo "acpi flr bus flr" > reset_method
   root# cat reset_method
   acpi flr bus flr

> + if (m == PCI_NUM_RESET_METHODS) {
> + kfree(options);
> + return -EINVAL;
Set the last entry to zero in pdev->reset_methods otherwise the inconsistent
methods are enabled.
Example:
   root# cat reset_method
   acpi flr bus

   root# echo "flr a" > reset_method
   root# cat reset_method
   flr flr bus

> +
> + }
> + }
> +
> + if (i < PCI_NUM_RESET_METHODS)
> + pdev->reset_methods[i] = 0;
> +
Last entry can be set unconditionally after removing the duplicate entries.
Refactored code to filter duplicate entries and warn the user about the invalid
& unsupported reset methods.

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);
        char *name, *options = NULL;
        int i, m, n = 0;

        if (count >= (PAGE_SIZE - 1))
                return -EINVAL;

        if (sysfs_streq(buf, ""))
                goto done;

        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);

                /* Validate reset method */
                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;
                }

                /* Check if the reset method is already enabled */
                for (i = 0; i < n; i++) {
                        if (pdev->reset_methods[i] == m)
                                break;
                }
                if (i < n)
                        continue;

                /* Probe the requested reset method */
                if (pci_reset_fn_methods[m].reset_fn(pdev, 1))
                        pci_warn(pdev, "Unsupported reset method '%s'", name);

                pdev->reset_methods[n++] = m;
                BUG_ON(n == PCI_NUM_RESET_METHODS)
       }
        kfree(options);

done:
        pdev->reset_methods[n] = 0;
        if (pdev->reset_methods[0] == 0) {
                pci_warn(pdev, "All device reset methods are disabled");
        } 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;
}