linux-kernel - Re: [RESEND PATCH 1/2] fpga: dfl: pci: reduce the scope of variable 'ret'

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Date:   Fri, 10 Jul 2020 13:16:00 +0800
From:   Xu Yilun <yilun.xu@...el.com>
To:     Tom Rix <trix@...hat.com>
Cc:     mdf@...nel.org, linux-fpga@...r.kernel.org,
        linux-kernel@...r.kernel.org, lgoncalv@...hat.com
Subject: Re: [RESEND PATCH 1/2] fpga: dfl: pci: reduce the scope of variable
  'ret'

On Thu, Jul 09, 2020 at 06:18:18AM -0700, Tom Rix wrote:
> I think a better change is to use the ret variable, like this
> 
> --- a/drivers/fpga/dfl-pci.c
> +++ b/drivers/fpga/dfl-pci.c
> @@ -312,7 +312,7 @@ static int cci_pci_sriov_configure(struct pci_dev *pcidev, int num_vfs)
>                 }
>         }
>  
> -       return num_vfs;
> +       return ret;
>  }
> 
> The existing use of returning num_vfs is not right, the function should return 0/err not num_vfs. currently it is reusing the 0 passed in with num_vfs to mean disable as the 0 return status.  it should be properly returning ret.

The sriov_configure callback should return negative value for error, and
return num_vfs if success.

See the Documentation/PCI/pci-iov-howto.rst

also in drivers/pci/iov.c:

  static ssize_t sriov_numvfs_store(struct device *dev, ...)
  {
	...

        ret = pdev->driver->sriov_configure(pdev, num_vfs);
        if (ret < 0) 
                goto exit;

        if (ret != num_vfs)
                pci_warn(pdev, "%d VFs requested; only %d enabled\n",
                         num_vfs, ret);

	...
  }

> 
> Tom
> 
> On 7/9/20 1:12 AM, Xu Yilun wrote:
> > This is to fix lkp cppcheck warnings:
> >
> >  drivers/fpga/dfl-pci.c:230:6: warning: The scope of the variable 'ret' can be reduced. [variableScope]
> >     int ret = 0;
> >         ^
> >
> >  drivers/fpga/dfl-pci.c:230:10: warning: Variable 'ret' is assigned a value that is never used. [unreadVariable]
> >     int ret = 0;
> >             ^
> >
> > Fixes: 3c2760b78f90 ("fpga: dfl: pci: fix return value of cci_pci_sriov_configure")
> > Reported-by: kbuild test robot <lkp@...el.com>
> > Signed-off-by: Xu Yilun <yilun.xu@...el.com>
> > Acked-by: Wu Hao <hao.wu@...el.com>
> > ---
> >  drivers/fpga/dfl-pci.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/fpga/dfl-pci.c b/drivers/fpga/dfl-pci.c
> > index 4a14a24..73b5153 100644
> > --- a/drivers/fpga/dfl-pci.c
> > +++ b/drivers/fpga/dfl-pci.c
> > @@ -285,7 +285,6 @@ static int cci_pci_sriov_configure(struct pci_dev *pcidev, int num_vfs)
> >  {
> >  	struct cci_drvdata *drvdata = pci_get_drvdata(pcidev);
> >  	struct dfl_fpga_cdev *cdev = drvdata->cdev;
> > -	int ret = 0;
> >  
> >  	if (!num_vfs) {
> >  		/*
> > @@ -297,6 +296,8 @@ static int cci_pci_sriov_configure(struct pci_dev *pcidev, int num_vfs)
> >  		dfl_fpga_cdev_config_ports_pf(cdev);
> >  
> >  	} else {
> > +		int ret;
> > +
> >  		/*
> >  		 * before enable SRIOV, put released ports into VF access mode
> >  		 * first of all.