3:10 a.m.
On Thu, Nov 12, 2020 at 04:43:01PM +0100, Miquel Raynal wrote:
Hi Serge,
Serge Semin <Sergey.Semin(a)baikalelectronics.ru> wrote on Thu, 12 Nov
2020 18:27:39 +0300:
> Hello Vignesh
>
> On Thu, Nov 12, 2020 at 08:30:42PM +0530, Vignesh Raghavendra wrote:
> >
> >
> > On 11/12/20 1:57 PM, Miquel Raynal wrote:
> > > Hi Sergey,
> > >
> > > Serge Semin <Sergey.Semin(a)baikalelectronics.ru> wrote on Wed, 11
Nov
> > > 2020 22:22:59 +0300:
> > >
> > >> On Tue, Nov 10, 2020 at 04:35:56PM +0100, Miquel Raynal wrote:
> > >>> Hi Serge,
> > >>>
> > >>> Serge Semin <Sergey.Semin(a)baikalelectronics.ru> wrote on
Tue, 10 Nov
> > >>> 2020 14:38:27 +0300:
> > >>>
> > >>>> Hello Miquel,
> > >>>>
> > >>>> A situation noted by the warning below won't cause any
problem because
> > >>>> the casting is done to a non-dereferenced variable. It is
utilized
> > >>>> as a pointer bias later in that function. Shall we just ignore
the
> > >>>> warning or still fix it somehow?
> > >>>
> > >>
> > >>> Do you think the cast to a !__iomem value is mandatory here?
> > >>
> > >> It's not mandatory to have the casting with no __iomem, but
wouldn't
> > >> doing like this:
> > >> + shift = (ssize_t __iomem)src & 0x3;
> > >> be looking weird? Really, is there a good way to somehow extract the
first
> > >> two bits of a __iomem pointer without getting the sparse warning?
> > >
> > > I asked around me, what about trying uintptr_t?
> > >
> >
>
> > One more way is to use __force to tell sparse that this casting is
> > intentional:
> >
> > shift = (__force ssize_t)src & 0x3;
>
> Oh, great! That solution is actually much better than using some
> currently unexplained sparse peculiarity! I was thinking about applying
> some other attribute, but __force just didn't come to my mind. Thank
> you very much for the suggestion. I'll post the fix with the solution
> suggested by you.
Is the ssize_t cast the right one btw? I would definitely prefer an
unsigned type here.
The reason of me deciding to use the ssize_t type here was to prevent
the types casting across the "shift", "chunk" and "len"
variables
within this method. It seemed a bit better than having a standard type
like "unsigned int" here seeing the ssize_t type width won't exceed
the long type size anyway. Moreover since the "len" variable has got
the ssize_t type and I couldn't change it (the method is the map_info
callback), I've decided to stick with what is available and defined
"shift" and "chunk" as ssize_t-es. Another callback method
bt1_rom_map_read() in his module has been designed in the same way.
Do you think it's better to change it in favor of using a different
type like "unsigned int" here anyway? If so for unification I'd need to
change bt1_rom_map_read() (though the "shift" variable has been
defined as "unsigned long" there in the first place because the offs
argument has got that type).
What to do with the __force attribute here? It does seem appropriate
even if for some mystical reasons we haven't got the sparse warning
for the unsigned types.
-Sergey
>
> Thanks,
> Miquèl