linux-kernel - Re: [PATCH v10 2/8] PCI: Add new array for keeping track of ordering of reset methods

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Date:   Wed, 28 Jul 2021 12:59:11 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Amey Narkhede <ameynarkhede03@...il.com>
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 2/8] PCI: Add new array for keeping track of ordering
 of reset methods

On Wed, Jul 28, 2021 at 11:15:19PM +0530, Amey Narkhede wrote:
> On 21/07/27 05:59PM, Bjorn Helgaas wrote:
> > On Fri, Jul 09, 2021 at 06:08:07PM +0530, Amey Narkhede wrote:
> > > Introduce a new array reset_methods in struct pci_dev to keep track of
> > > reset mechanisms supported by the device and their ordering.
> > >
> > > Also refactor probing and reset functions to take advantage of calling
> > > convention of reset functions.
> > >
> > > 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>
> > > ---
> > >  drivers/pci/pci.c   | 92 ++++++++++++++++++++++++++-------------------
> > >  drivers/pci/pci.h   |  9 ++++-
> > >  drivers/pci/probe.c |  5 +--
> > >  include/linux/pci.h |  7 ++++
> > >  4 files changed, 70 insertions(+), 43 deletions(-)
> > >
> >
> [...]
> > > +	BUILD_BUG_ON(ARRAY_SIZE(pci_reset_fn_methods) != PCI_NUM_RESET_METHODS);
> > >
> > >  	might_sleep();
> > >
> > > -	rc = pci_dev_specific_reset(dev, 1);
> > > -	if (rc != -ENOTTY)
> > > -		return rc;
> > > -	rc = pcie_reset_flr(dev, 1);
> > > -	if (rc != -ENOTTY)
> > > -		return rc;
> > > -	rc = pci_af_flr(dev, 1);
> > > -	if (rc != -ENOTTY)
> > > -		return rc;
> > > -	rc = pci_pm_reset(dev, 1);
> > > -	if (rc != -ENOTTY)
> > > -		return rc;
> > > +	for (i = 1; i < PCI_NUM_RESET_METHODS; i++) {
> > > +		rc = pci_reset_fn_methods[i].reset_fn(dev, 1);
> > > +		if (!rc)
> > > +			reset_methods[n++] = i;
> >
> > Why do we need this local reset_methods[] array?  Can we just fill
> > in dev->reset_methods[] directly and skip the memcpy() below?
> >
> This is for avoiding caching of previously supported reset methods.
> Is it okay if I use memset(dev->reset_methods, 0,
> sizeof(dev->reset_methods)) instead to clear the values in
> dev->reset_methods?

I don't think there's ever a case where you look at a
dev->reset_methods[] element past a zero value, so we shouldn't care
about any previously-supported methods left in the array.

If we *do* look at something past a zero value, why do we do that?  It
sounds like it would be a bug.

> > > +		else if (rc != -ENOTTY)
> > > +			break;
> > > +	}
> > >
> > > -	return pci_reset_bus_function(dev, 1);
> > > +	memcpy(dev->reset_methods, reset_methods, sizeof(reset_methods));
> > >  }
> > >
> > >  /**
> [...]