Re: [PATCH] PCI: Add cast when assigning PCI_ROM_ADDRESS_MASK to a 32-bit variable

From: Matthias Kaehlcke
Date: Tue Apr 11 2017 - 13:23:23 EST


El Tue, Apr 11, 2017 at 12:08:38PM +0200 Mason ha dit:

> On 11/04/2017 03:24, Bjorn Helgaas wrote:
>
> > On Mon, Apr 10, 2017 at 03:24:57PM -0700, Matthias Kaehlcke wrote:
> >
> >> This fixes a clang warning about "implicit conversion from 'unsigned
> >> long' to 'u32'"
> >>
> >> Signed-off-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
> >> ---
> >> drivers/pci/probe.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> >> index dfc9a2794141..148e80d5caf1 100644
> >> --- a/drivers/pci/probe.c
> >> +++ b/drivers/pci/probe.c
> >> @@ -180,7 +180,7 @@ int __pci_read_base(struct pci_dev *dev, enum pci_bar_type type,
> >> u16 orig_cmd;
> >> struct pci_bus_region region, inverted_region;
> >>
> >> - mask = type ? PCI_ROM_ADDRESS_MASK : ~0;
> >> + mask = type ? (u32)PCI_ROM_ADDRESS_MASK : ~0;
> >
> > Can we put the cast in the PCI_ROM_ADDRESS_MASK #define so we don't have to
> > repeat it in all the uses?
>
> Fixing these "implicit conversion" warnings, especially for
> unsigned types, is a slippery slope. (The behavior of the
> conversion is well-defined.)
>
> How about changing the type of PCI_ROM_ADDRESS_MASK instead?
> It's defined as ~0x7ffUL but it's only used in the context
> of u32.
>
> So make it an unsigned int:
> #define PCI_ROM_ADDRESS_MASK (~0x7ffU)
>
> AFAIU, unsigned int is 32 bits on all platforms supported
> by Linux.

I considered this initially, but wasn't sure if the unsigned long
mask might be needed in some cases. From the comments I interpret that
there should be no problems with using a 32 bit mask everywhere.

I'll send out an updated patch shortly.

Thanks

Matthias