Re: [PATCH] PCI: tegra: Fix shiftTooManyBitsSigned warning for Tegra194

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Jun 18, 2021 at 06:04:28PM -0500, Bjorn Helgaas wrote:
> On Fri, Jun 18, 2021 at 05:02:19PM +0100, Jon Hunter wrote:
> > The cppcheck tool issues the following warning for the Tegra194 PCIe
> > driver ...
> > 
> >  $ cppcheck --enable=all drivers/pci/controller/dwc/pcie-tegra194.c
> >  Checking drivers/pci/controller/dwc/pcie-tegra194.c ...
> > 
> >  drivers/pci/controller/dwc/pcie-tegra194.c:1829:23: portability:
> > 	Shifting signed 32-bit value by 31 bits is
> > 	implementation-defined behaviour. See condition at line 1826.
> > 	[shiftTooManyBitsSigned]
> > 
> >   appl_writel(pcie, (1 << irq), APPL_MSI_CTRL_1);
> >                       ^
> > The above warning occurs because the '1' is treated as a signed type
> > and so fix this by using the 'BIT' macro to ensure that this is defined
> > as a unsigned type.
> 
> The subject and commit log should describe the problem we're fixing.
> The *warning* is not the problem; the problem is the undefined
> behavior.
> 
> I'll fix this up, no need to repost for this.

I merged this from Lorenzo's branch, but I updated the commit log like
this because the undefined behavior is the real problem:

    PCI: tegra194: Fix tegra_pcie_ep_raise_msi_irq() ill-defined shift

    tegra_pcie_ep_raise_msi_irq() shifted a signed 32-bit value left by 31
    bits.  The behavior of this is implementation-defined.

    Replace the shift by BIT(), which is well-defined.

    Found by cppcheck:

      $ cppcheck --enable=all drivers/pci/controller/dwc/pcie-tegra194.c
      Checking drivers/pci/controller/dwc/pcie-tegra194.c ...

      drivers/pci/controller/dwc/pcie-tegra194.c:1829:23: portability: Shifting signed 32-bit value by 31 bits is implementation-defined behaviour. See condition at line 1826.  [shiftTooManyBitsSigned]

      appl_writel(pcie, (1 << irq), APPL_MSI_CTRL_1);
                         ^

    [bhelgaas: commit log]
    Link: https://lore.kernel.org/r/20210618160219.303092-1-jonathanh@nvidia.com
    Fixes: c57247f940e8 ("PCI: tegra: Add support for PCIe endpoint mode in Tegra194")
    Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
    Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
    Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

> > Fixes: c57247f940e8 PCI: tegra: Add support for PCIe endpoint mode in Tegra194
> > Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
> > ---
> >  drivers/pci/controller/dwc/pcie-tegra194.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c b/drivers/pci/controller/dwc/pcie-tegra194.c
> > index 8fc08336f76e..3c1feeab104f 100644
> > --- a/drivers/pci/controller/dwc/pcie-tegra194.c
> > +++ b/drivers/pci/controller/dwc/pcie-tegra194.c
> > @@ -1826,7 +1826,7 @@ static int tegra_pcie_ep_raise_msi_irq(struct tegra_pcie_dw *pcie, u16 irq)
> >  	if (unlikely(irq > 31))
> >  		return -EINVAL;
> >  
> > -	appl_writel(pcie, (1 << irq), APPL_MSI_CTRL_1);
> > +	appl_writel(pcie, BIT(irq), APPL_MSI_CTRL_1);
> >  
> >  	return 0;
> >  }
> > -- 
> > 2.25.1
> >