linux-kernel - Re: [PATCH v10 4/8] PCI/sysfs: Allow userspace to query and set device reset mechanism

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Message-ID: <20210731191505.xzor5lpqv4ubmijf@archlinux>
Date:   Sun, 1 Aug 2021 00:45:05 +0530
From:   Amey Narkhede <ameynarkhede03@...il.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     alex.williamson@...hat.com,
        Raphael Norwitz <raphael.norwitz@...anix.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        kw@...ux.com, Shanker Donthineni <sdonthineni@...dia.com>,
        Sinan Kaya <okaya@...nel.org>, Len Brown <lenb@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH v10 4/8] PCI/sysfs: Allow userspace to query and set
 device reset mechanism

On 21/07/27 06:28PM, Bjorn Helgaas wrote:
> On Fri, Jul 09, 2021 at 06:08:09PM +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@...hat.com>
> > Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> > Signed-off-by: Amey Narkhede <ameynarkhede03@...il.com>
> > ---
> >  Documentation/ABI/testing/sysfs-bus-pci |  19 +++++
> >  drivers/pci/pci-sysfs.c                 | 103 ++++++++++++++++++++++++
> >  2 files changed, 122 insertions(+)
> >
[...]

> > +		if (i == PCI_NUM_RESET_METHODS) {
> > +			kfree(options);
> > +			return -EINVAL;
> > +		}
> > +	}
> > +
> > +	if (!pci_reset_fn_methods[1].reset_fn(pdev, 1) && reset_methods[0] != 1)
> > +		pci_warn(pdev, "Device specific reset disabled/de-prioritized by user");
>
> Hmmm.  I sort of see the point here, but I wish we didn't have the
> implicit dependency on pci_reset_fn_methods[1] being
> pci_dev_specific_reset().
>
> I know we've talked about this before.  I'm still not 100% sure either
> of these warnings is worthwhile, especially since we're not *using*
> the reset here.  It might be useful at the point where we try to *do*
> a reset.  I dunno.  Maybe this is the best place since this is where
> the user potentially screwed up.
>
I agree this is the best place for the warning as this where potentially
broken reset methods may get called/prioritized. We can move this check
to __pci_reset_function_locked() if you want.

> > +set_reset_methods:
> > +	memcpy(pdev->reset_methods, reset_methods, sizeof(reset_methods));
> > +	kfree(options);
> > +	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;
> > +}
> > +
> > +static 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,
> > +};
> > +
> >  static ssize_t reset_store(struct device *dev, struct device_attribute *attr,
> >  			   const char *buf, size_t count)
> >  {
> > @@ -1491,6 +1593,7 @@ 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,
> > --
> > 2.32.0
> >