Re: [PATCH v7 4/8] PCI/sysfs: Allow userspace to query and set device reset mechanism

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Jun 08, 2021 at 11:18:53AM +0530, Amey Narkhede wrote:
> Add reset_method sysfs attribute to enable user to
> query and set user preferred device reset methods and
> their ordering.

> +		Writing the name or comma 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.

> +	while ((name = strsep(&options, ",")) != NULL) {
> +		if (sysfs_streq(name, ""))
> +			continue;
> +
> +		name = strim(name);
> +
> +		for (i = 0; i < PCI_RESET_METHODS_NUM; i++) {
> +			if (reset_methods[i] &&
> +			    sysfs_streq(name, pci_reset_fn_methods[i].name)) {
> +				reset_methods[i] = prio--;
> +				break;
> +			}
> +		}
> +
> +		if (i == PCI_RESET_METHODS_NUM) {
> +			kfree(options);
> +			return -EINVAL;
> +		}
> +	}

Asking again since we didn't get this clarified before.  The above
tells me that "reset_methods" allows the user to control the *order*
in which we try reset methods.

Consider the following two uses:

  (1) # echo bus,flr > reset_methods

  (2) # echo flr,bus > reset_methods

Do these have the same effect or not?

If "reset_methods" allows control over the order, I expect them to be
different: (1) would try a bus reset and, if the bus reset failed, an
FLR, while (2) would try an FLR and, if the FLR failed, a bus reset.