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Date:   Thu, 6 Apr 2023 14:42:06 +0200
From:   Simon Horman <simon.horman@corigine.com>
To:     Denis Plotnikov <den-plotnikov@yandex-team.ru>
Cc:     Bjorn Helgaas <helgaas@kernel.org>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, shshaikh@marvell.com,
        manishc@marvell.com, GR-Linux-NIC-Dev@marvell.com,
        davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
        pabeni@redhat.com, Bjorn Helgaas <bhelgaas@google.com>,
        linux-pci@vger.kernel.org
Subject: Re: [PATCH] qlcnic: check pci_reset_function result
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On Thu, Apr 06, 2023 at 01:43:44PM +0200, Simon Horman wrote:
> On Thu, Apr 06, 2023 at 12:23:49PM +0300, Denis Plotnikov wrote:
> > 
> > On 06.04.2023 10:03, Simon Horman wrote:
> > > On Wed, Apr 05, 2023 at 02:37:08PM -0500, Bjorn Helgaas wrote:
> > > > On Wed, Apr 05, 2023 at 03:04:39PM +0200, Simon Horman wrote:
> > > > > On Mon, Apr 03, 2023 at 01:58:49PM +0300, Denis Plotnikov wrote:
> > > > > > On 31.03.2023 20:52, Simon Horman wrote:
> > > > > > > On Fri, Mar 31, 2023 at 11:06:05AM +0300, Denis Plotnikov wrote:
> > > > > > > > Static code analyzer complains to unchecked return value.
> > > > > > > > It seems that pci_reset_function return something meaningful
> > > > > > > > only if "reset_methods" is set.
> > > > > > > > Even if reset_methods isn't used check the return value to avoid
> > > > > > > > possible bugs leading to undefined behavior in the future.
> > > > > > > > 
> > > > > > > > Signed-off-by: Denis Plotnikov <den-plotnikov@yandex-team.ru>
> > > > > > > nit: The tree this patch is targeted at should be designated, probably
> > > > > > >        net-next, so the '[PATCH net-next]' in the subject.
> > > > > > > 
> > > > > > > > ---
> > > > > > > >    drivers/net/ethernet/qlogic/qlcnic/qlcnic_ctx.c | 4 +++-
> > > > > > > >    1 file changed, 3 insertions(+), 1 deletion(-)
> > > > > > > > 
> > > > > > > > diff --git a/drivers/net/ethernet/qlogic/qlcnic/qlcnic_ctx.c b/drivers/net/ethernet/qlogic/qlcnic/qlcnic_ctx.c
> > > > > > > > index 87f76bac2e463..39ecfc1a1dbd0 100644
> > > > > > > > --- a/drivers/net/ethernet/qlogic/qlcnic/qlcnic_ctx.c
> > > > > > > > +++ b/drivers/net/ethernet/qlogic/qlcnic/qlcnic_ctx.c
> > > > > > > > @@ -628,7 +628,9 @@ int qlcnic_fw_create_ctx(struct qlcnic_adapter *dev)
> > > > > > > >    	int i, err, ring;
> > > > > > > >    	if (dev->flags & QLCNIC_NEED_FLR) {
> > > > > > > > -		pci_reset_function(dev->pdev);
> > > > > > > > +		err = pci_reset_function(dev->pdev);
> > > > > > > > +		if (err && err != -ENOTTY)
> > > > > > > Are you sure about the -ENOTTY part?
> > > > > > > 
> > > > > > > It seems odd to me that an FLR would be required but reset is not supported.
> > > > > > No, I'm not sure. My logic is: if the reset method isn't set than
> > > > > > pci_reset_function() returns -ENOTTY so treat that result as ok.
> > > > > > pci_reset_function may return something different than -ENOTTY only if
> > > > > > pci_reset_fn_methods[m].reset_fn is set.
> > > > > I see your reasoning: -ENOTTY means nothing happened, and probably that is ok.
> > > > > I think my main question is if that can ever happen.
> > > > > If that is unknown, then I think this conservative approach makes sense.
> > > > The commit log mentions "reset_methods", which I don't think is really
> > > > relevant here because reset_methods is an internal implementation
> > > > detail.  The point is that pci_reset_function() returns 0 if it was
> > > > successful and a negative value if it failed.
> > > > 
> > > > If the driver thinks the device needs to be reset, ignoring any
> > > > negative return value seems like a mistake because the device was not
> > > > reset.
> > > > 
> > > > If the reset is required for a firmware update to take effect, maybe a
> > > > diagnostic would be helpful if it fails, e.g., the other "Adapter
> > > > initialization failed.  Please reboot" messages.
> > > > 
> > > > "QLCNIC_NEED_FLR" suggests that the driver expects an FLR (as opposed
> > > > to other kinds of reset).  If the driver knows that all qlcnic devices
> > > > support FLR, it could use pcie_flr() directly.
> > > > 
> > > > pci_reset_function() does have the possibility that the reset works on
> > > > some devices but not all.  Secondary Bus Reset fails if there are
> > > > other functions on the same bus, e.g., a multi-function device.  And
> > > > there's some value in doing the reset the same way in all cases.
> > > > 
> > > > So I would suggest something like:
> > > > 
> > > >    if (dev->flags & QLCNIC_NEED_FLR) {
> > > >      err = pcie_flr(dev->pdev);
> > > >      if (err) {
> > > >        dev_err(&pdev->dev, "Adapter reset failed (%d). Please reboot\n", err);
> > > >        return err;
> > > >      }
> > > >      dev->flags &= ~QLCNIC_NEED_FLR;
> > > >    }
> > > > 
> > > > Or, if there are qlcnic devices that don't support FLR:
> > > > 
> > > >    if (dev->flags & QLCNIC_NEED_FLR) {
> > > >      err = pci_reset_function(dev->pdev);
> > > >      if (err) {
> > > >        dev_err(&pdev->dev, "Adapter reset failed (%d). Please reboot\n", err);
> > > >        return err;
> > > >      }
> > > >      dev->flags &= ~QLCNIC_NEED_FLR;
> > > >    }
> > > Thanks Bjorn,
> > > 
> > > that is very helpful.
> > > 
> > > I think that in order to move to option #1 some information would be needed
> > > from those familiar with the device(s). As it is a more invasive change -
> > > pci_reset_function -> pcie_flr.
> > > 
> > > So my feeling is that, in lieu of such feedback, option #2 is a good
> > > improvement on the current code.
> > > 
> > > OTOH, this driver is 'Supported' as opposed to 'Maintained'.
> > > So perhaps we can just use our best judgement and go for option #1.
> > 
> > So, it looks like option #2 is the safest choice as we do reset only if FLR
> > is needed (when pci_reset_function() makes sense)
> > 
> > If all agree with that I'll re-send the path
> 
> Yes. Maybe wait 24h, and if there is no further feedback go ahead with that
> plan?

Perhaps a code comment, or the patch description could include
some information about the reasoning above.