netdev - Re: [PATCH] qlcnic: check pci_reset

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Date:   Thu, 6 Apr 2023 09:03:36 +0200
From:   Simon Horman <simon.horman@...igine.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Denis Plotnikov <den-plotnikov@...dex-team.ru>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        shshaikh@...vell.com, manishc@...vell.com,
        GR-Linux-NIC-Dev@...vell.com, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org
Subject: Re: [PATCH] qlcnic: check pci_reset_function result

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@...dex-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.