Messages in this thread | | | Date | Thu, 12 Nov 2020 19:10:43 +0300 | From | Serge Semin <> | Subject | Re: drivers/mtd/maps/physmap-bt1-rom.c:78:18: sparse: sparse: cast removes address space '__iomem' of expression |
| |
On Thu, Nov 12, 2020 at 04:43:01PM +0100, Miquel Raynal wrote: > Hi Serge, > > Serge Semin <Sergey.Semin@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@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@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
| |