On Mon, Sep 21, 2020 at 17:36:24, Bjorn Helgaas <helgaas@xxxxxxxxxx>
wrote:
> On Mon, Sep 21, 2020 at 11:30:48AM +0000, Gustavo Pimentel wrote:
> > On Fri, Sep 18, 2020 at 8:15:48, Gustavo Pimentel <gustavo@xxxxxxxxxxxx>
> > wrote:
> >
> > > On Thu, Sep 17, 2020 at 22:47:59, Bjorn Helgaas <helgaas@xxxxxxxxxx>
> > > wrote:
> > >
> > > > On Thu, Sep 17, 2020 at 11:28:03PM +0200, Gustavo Pimentel wrote:
> > > > > Fixes warning given by executing "make C=2 drivers/pci/"
> > > > >
> > > > > Sparse output:
> > > > > CHECK drivers/pci/controller/dwc/pcie-designware.c
> > > > > drivers/pci/controller/dwc/pcie-designware.c:432:52: warning:
> > > > > cast truncates bits from constant value (ffffffff7fffffff becomes
> > > > > 7fffffff)
> > > > >
> > > > > Reported-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> > > > > Cc: Joao Pinto <jpinto@xxxxxxxxxxxx>
> > > > > Signed-off-by: Gustavo Pimentel <gustavo.pimentel@xxxxxxxxxxxx>
> > > > > ---
> > > > > drivers/pci/controller/dwc/pcie-designware.c | 2 +-
> > > > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> > > > > index 3c3a4d1..dcb7108 100644
> > > > > --- a/drivers/pci/controller/dwc/pcie-designware.c
> > > > > +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > > > > @@ -429,7 +429,7 @@ 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, (u32)~PCIE_ATU_ENABLE);
> > > > > + dw_pcie_writel_dbi(pci, PCIE_ATU_CR2, (u32)~0 & ~PCIE_ATU_ENABLE);
> > > >
> > > > But this cure is worse than the disease. If this is the only way to
> > > > fix the warning, I think I'd rather see the warning ;) I'm hopeful
> > > > there's a nicer way, but I'm not a language lawyer.
> > >
> > > I don't like it either, I tried to see if were another way a clean way
> > > that didn't imply creating a temporary variable, but I didn't found.
> > > The issue here is that PCIE_ATU_ENABLE is defined as BIT(31) on
> > > pcie-designware.h. The macro BIT changes its size from u32 to u64
> > > according to the architecture and by inverting the value on the 64 bits
> > > architecture causes the value to be transformed into 0xffffffff7fffffff.
> > >
> > > The other possibility implies the creation of a temporary u32 variable to
> > > overcome this issue. It's a little bit overkill, but please share your
> > > thoughts about it.
> > >
> > > void dw_pcie_disable_atu(struct dw_pcie *pci, int index,
> > > enum dw_pcie_region_type type)
> > > {
> > > - int region;
> > > + u32 atu = PCIE_ATU_ENABLE;
> > > + u32 region;
> > >
> > > switch (type) {
> > > case DW_PCIE_REGION_INBOUND:
> > > @@ -429,7 +430,7 @@ 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, (u32)~PCIE_ATU_ENABLE);
> > > + dw_pcie_writel_dbi(pci, PCIE_ATU_CR2, ~atu);
> > > }
> >
> > Hi Bjorn,
> >
> > What is your verdict on this?
> > If you prefer this approach I can send the corresponding patch.
>
> Having a u32 temporary with no obvious reason for existence is kind of
> unpleasant, too. Surely this is a common situation? Maybe other
> instances just live with the warning, too?
>
> I'd say leave this alone for now.
Hi Bjorn,
After resting about this topic, I found a easy and clean solution that
will please for both of us.
- dw_pcie_writel_dbi(pci, PCIE_ATU_CR2, (u32)~PCIE_ATU_ENABLE);
+ dw_pcie_writel_dbi(pci, PCIE_ATU_CR2, ~(u32)PCIE_ATU_ENABLE);
Basically I changed the cast instruction position, this way the
PCIE_ATU_ENABLE flag defined BIT(31) on a 64 bits architecture will be
casted into a u32 and the binary one's complement instruction will act
upon a 32bits variable, avoiding that error.
I'll send the patch for it right away.
-Gustavo
>
> Bjorn
