linux-kernel - Re: [PATCH] PCI: tegra: Use PTR_ERR_OR

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Message-ID: <20170830135931.GA18250@bhelgaas-glaptop.roam.corp.google.com>
Date:   Wed, 30 Aug 2017 08:59:31 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Himanshu Jha <himanshujha199640@...il.com>, bhelgaas@...gle.com,
        jonathanh@...dia.com, linux-tegra@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: tegra: Use PTR_ERR_OR_ZERO

On Tue, Aug 29, 2017 at 03:55:17PM +0200, Thierry Reding wrote:
> On Tue, Aug 29, 2017 at 07:09:00PM +0530, Himanshu Jha wrote:
> > Use PTR_ERR_OR_ZERO rather than if(IS_ERR(...)) + PTR_ERR
> > 
> > Signed-off-by: Himanshu Jha <himanshujha199640@...il.com>
> > ---
> >  drivers/pci/host/pci-tegra.c | 5 +----
> >  1 file changed, 1 insertion(+), 4 deletions(-)
> > 
> > diff --git a/drivers/pci/host/pci-tegra.c b/drivers/pci/host/pci-tegra.c
> > index 9c40da5..90cda5b 100644
> > --- a/drivers/pci/host/pci-tegra.c
> > +++ b/drivers/pci/host/pci-tegra.c
> > @@ -1156,10 +1156,7 @@ static int tegra_pcie_resets_get(struct tegra_pcie *pcie)
> >  		return PTR_ERR(pcie->afi_rst);
> >  
> >  	pcie->pcie_xrst = devm_reset_control_get_exclusive(dev, "pcie_x");
> > -	if (IS_ERR(pcie->pcie_xrst))
> > -		return PTR_ERR(pcie->pcie_xrst);
> > -
> > -	return 0;
> > +	return PTR_ERR_OR_ZERO(pcie->pcie_xrst);
> >  }
> 
> I'm not a big fan of this construct because it's a pain to undo this if
> ever we need to add code to this function. But since we do have scripts
> that will flag this, I guess this would pop up every now and again. The
> driver is unlikely to change in this part, too, so:

Thanks for pointing this out.  Do you know what the benefit of
PTR_ERR_OR_ZERO() is?  To me, it makes the following code harder
to read because the error tests are no longer parallel:

  ...
  res->ahb_reset = devm_reset_control_get(dev, "ahb");
  if (IS_ERR(res->ahb_reset))
    return PTR_ERR(res->ahb_reset);

  res->por_reset = devm_reset_control_get(dev, "por");
  if (IS_ERR(res->por_reset))
    return PTR_ERR(res->por_reset);

  res->phy_reset = devm_reset_control_get(dev, "phy");
  return PTR_ERR_OR_ZERO(res->phy_reset);

So I'd be inclined to avoid it unless there's some significant benefit.

Bjorn