On Wed, Jun 18, 2014 at 09:49:39AM +0300, Alexey Tulia wrote:
> On Tue, Jun 17, 2014 at 03:44:58PM -0700, Greg Kroah-Hartman wrote:
> > On Fri, Jun 13, 2014 at 11:35:13AM +0300, Alexey Tulia wrote:
> > > This fixes the following warning:
> > > - WARNING: __constant_cpu_to_le32 should be cpu_to_le32
> >
> > What produces this warning?
> >
>
> This warning was found by checkpatch.pl -f
>
> > >
> > > Signed-off-by: Alexey Tulia <alexey.tulia@xxxxxxxxx>
> > > ---
> > > drivers/staging/usbip/vhci_hcd.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/staging/usbip/vhci_hcd.c b/drivers/staging/usbip/vhci_hcd.c
> > > index 0007d30..e21c1b4 100644
> > > --- a/drivers/staging/usbip/vhci_hcd.c
> > > +++ b/drivers/staging/usbip/vhci_hcd.c
> > > @@ -304,7 +304,7 @@ static int vhci_hub_control(struct usb_hcd *hcd, u16 typeReq, u16 wValue,
> > > break;
> > > case GetHubStatus:
> > > usbip_dbg_vhci_rh(" GetHubStatus\n");
> > > - *(__le32 *) buf = __constant_cpu_to_le32(0);
> > > + *(__le32 *) buf = cpu_to_le32(0);
> >
> > How is this correct? Why shouldn't __constant_cpu_to_le32() be used
> > here? Heck, why can't we just use 0 given that it doesn't matter the
> > endianness of that specific value :)
>
> It may be so, but anyway the __constant_cpu_to_le32 produced a warning
> and it was obvious to clean up this part of code a bit.
> However, the 0 value possibly can change to other value in future and
> this macro acts as a safety net here.
Dragging Joe in here as he wrote that checkpatch feature.
Joe, how is not using __constant_cpu_to_* a good thing? If I have a
constant value, cpu_to_* will be a function call if the bits have to be
switched around (no-op if not). I don't see the code path that detects
a constant value and calls the swap-bits-as-a-constant macro instead,
unless the __constant_cpu_to* function is called.
Am I just missing it somewhere in the .h include chain?
thanks,
greg k-h
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