El Sat, Mar 11, 2017 at 01:03:48PM +0100 Heiko Stuebner ha dit:
> Hi Matthias,
>
> Am Freitag, 10. März 2017, 18:21:53 CET schrieb Matthias Kaehlcke:
> > The following warning is generated when building with clang:
> >
> > drivers/soc/rockchip/pm_domains.c:726:22: error: shift count is negative
> > [-Werror,-Wshift-count-negative] [RK3399_PD_TCPD0] = DOMAIN_RK3399(8,
> > 8, -1, false),
> > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > drivers/soc/rockchip/pm_domains.c:101:2: note: expanded from macro
> > 'DOMAIN_RK3399' DOMAIN(pwr, status, req, req, req, wakeup)
> > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > drivers/soc/rockchip/pm_domains.c:88:27: note: expanded from macro 'DOMAIN'
> > .req_mask = (req >= 0) ? BIT(req) : 0, \
> > ^~~~~~~~
> > include/linux/bitops.h:6:24: note: expanded from macro 'BIT'
> >
> > The BIT macro is evaluated with the negative value -1, even though the
> > resulting value would not be assigned. To fix this we only pass values
> > between 0 and 63 to BIT(). Unfortunately this means that we lose the
> > benefit of the compiler checking for out of bounds errors.
>
> I tend to disagree here. This looks more like a case of "fix your compiler".
>
> That conditional seems perfectly valid as the BIT(req) will never be reached
> if req < 0 - your clang simply doesn't recognize the pattern somehow, while
> for example gcc does.
My interpretation is that with clang the '(req >= 0) ?' condition is
not evaluated by the preprocessor, but only by the compiler. This seems to
be different with gcc.
> Catering to specific whims of specific compilers feels somehow wrong, as what
> will happen if some imaginary third compiler requires another different hack
> to be satisfied?
I'll check with the clang developers if clang can be changed to behave
like gcc in this aspect.
Thanks
Matthias
> > Signed-off-by: Matthias Kaehlcke <m...@chromium.org>
> > ---
> > drivers/soc/rockchip/pm_domains.c | 14 ++++++++------
> > 1 file changed, 8 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/soc/rockchip/pm_domains.c
> > b/drivers/soc/rockchip/pm_domains.c index 1c78c42416c6..6f2bb1222992 100644
> > --- a/drivers/soc/rockchip/pm_domains.c
> > +++ b/drivers/soc/rockchip/pm_domains.c
> > @@ -77,13 +77,15 @@ struct rockchip_pmu {
> >
> > #define to_rockchip_pd(gpd) container_of(gpd, struct rockchip_pm_domain,
> > genpd)
> >
> > +#define RK_MASK(bit) ((bit >= 0) ? BIT(bit & 0x3f) : 0)
> > +
> > #define DOMAIN(pwr, status, req, idle, ack, wakeup) \
> > -{ \
> > - .pwr_mask = (pwr >= 0) ? BIT(pwr) : 0, \
> > - .status_mask = (status >= 0) ? BIT(status) : 0, \
> > - .req_mask = (req >= 0) ? BIT(req) : 0, \
> > - .idle_mask = (idle >= 0) ? BIT(idle) : 0, \
> > - .ack_mask = (ack >= 0) ? BIT(ack) : 0, \
> > +{ \
> > + .pwr_mask = RK_MASK(pwr), \
> > + .status_mask = RK_MASK(status), \
> > + .req_mask = RK_MASK(req), \
> > + .idle_mask = RK_MASK(idle), \
> > + .ack_mask = RK_MASK(ack), \
> > .active_wakeup = wakeup, \
> > }
>
>
