linux-kernel - Re: [PATCH 11/21] PCI: designware: Make use of BIT() in constant definitions

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Date:   Wed, 2 Jan 2019 10:28:09 -0800
From:   Andrey Smirnov <andrew.smirnov@...il.com>
To:     Gustavo Pimentel <gustavo.pimentel@...opsys.com>
Cc:     "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Fabio Estevam <fabio.estevam@....com>,
        Chris Healy <cphealy@...il.com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Leonard Crestez <leonard.crestez@....com>,
        "A.s. Dong" <aisheng.dong@....com>,
        Richard Zhu <hongxing.zhu@....com>,
        "linux-imx@....com" <linux-imx@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 11/21] PCI: designware: Make use of BIT() in constant definitions

On Wed, Dec 26, 2018 at 7:19 AM Gustavo Pimentel
<gustavo.pimentel@...opsys.com> wrote:
>
> Hi,
>
> On 21/12/2018 07:27, Andrey Smirnov wrote:
> > Avoid using explicit left shifts and convert various definitions to
> > use BIT() instead. No functional change intended.
> >
> > Cc: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> > Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> > Cc: Fabio Estevam <fabio.estevam@....com>
> > Cc: Chris Healy <cphealy@...il.com>
> > Cc: Lucas Stach <l.stach@...gutronix.de>
> > Cc: Leonard Crestez <leonard.crestez@....com>
> > Cc: "A.s. Dong" <aisheng.dong@....com>
> > Cc: Richard Zhu <hongxing.zhu@....com>
> > Cc: linux-imx@....com
> > Cc: linux-arm-kernel@...ts.infradead.org
> > Cc: linux-kernel@...r.kernel.org
> > Cc: linux-pci@...r.kernel.org
> > Signed-off-by: Andrey Smirnov <andrew.smirnov@...il.com>
> > ---
> >  drivers/pci/controller/dwc/pcie-designware.c |  2 +-
> >  drivers/pci/controller/dwc/pcie-designware.h | 18 +++++++++---------
> >  2 files changed, 10 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> > index d123ac290b9e..086e87a40316 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > @@ -300,7 +300,7 @@ void dw_pcie_disable_atu(struct dw_pcie *pci, int index,
> >       }
> >
> >       dw_pcie_writel_dbi(pci, PCIE_ATU_VIEWPORT, region | index);
> > -     dw_pcie_writel_dbi(pci, PCIE_ATU_CR2, ~PCIE_ATU_ENABLE);
> > +     dw_pcie_writel_dbi(pci, PCIE_ATU_CR2, (u32)~PCIE_ATU_ENABLE);
>
> This is unrelated with the patch description purpose.
>

This is a direct result of converting PCIE_ATU_ENABLE to BIT(31).
BIT(31) expands to (1UL << 31) so, without that cast I get

drivers/pci/controller/dwc/pcie-designware.c: In function
‘dw_pcie_disable_atu’:
drivers/pci/controller/dwc/pcie-designware.c:303:40: warning: large
integer implicitly truncated to unsigned type [-Woverflow]
  dw_pcie_writel_dbi(pci, PCIE_ATU_CR2, ~PCIE_ATU_ENABLE);

on AArch64. I am guessing that original definition of (1 << 31) avoids
this problem by being an "int" instead of "unsigned long".

Thanks,
Andrey Smirnov