tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master head: 3cea11cd5e3b00d91caf0b4730194039b45c5891 commit: b3e79e7682e075326df8041b826b03453acacd0a mtd: physmap: Add Baikal-T1 physically mapped ROM support date: 4 weeks ago config: sparc64-randconfig-s032-20201031 (attached as .config) compiler: sparc64-linux-gcc (GCC) 9.3.0 reproduce: wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross chmod +x ~/bin/make.cross # apt-get install sparse # sparse version: v0.6.3-76-gf680124b-dirty # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit... git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git git fetch --no-tags linus master git checkout b3e79e7682e075326df8041b826b03453acacd0a # save the attached .config to linux build tree COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' ARCH=sparc64 If you fix the issue, kindly add following tag as appropriate Reported-by: kernel test robot <lkp(a)intel.com&gt; "sparse warnings: (new ones prefixed by >>)" >> drivers/mtd/maps/physmap-bt1-rom.c:78:18: sparse: sparse: cast removes address space '__iomem' of expression vim +/__iomem +78 drivers/mtd/maps/physmap-bt1-rom.c 57 58 static void __xipram bt1_rom_map_copy_from(struct map_info *map, 59 void *to, unsigned long from, 60 ssize_t len) 61 { 62 void __iomem *src = map->virt + from; 63 ssize_t shift, chunk; 64 u32 data; 65 66 if (len <= 0 || from >= map->size) 67 return; 68 69 /* Make sure we don't go over the map limit. */ 70 len = min_t(ssize_t, map->size - from, len); 71 72 /* 73 * Since requested data size can be pretty big we have to implement 74 * the copy procedure as optimal as possible. That's why it's split 75 * up into the next three stages: unaligned head, aligned body, 76 * unaligned tail. 77 */ > 78 shift = (ssize_t)src & 0x3; 79 if (shift) { 80 chunk = min_t(ssize_t, 4 - shift, len); 81 data = readl_relaxed(src - shift); 82 memcpy(to, &data + shift, chunk); 83 src += chunk; 84 to += chunk; 85 len -= chunk; 86 } 87 88 while (len >= 4) { 89 data = readl_relaxed(src); 90 memcpy(to, &data, 4); 91 src += 4; 92 to += 4; 93 len -= 4; 94 } 95 96 if (len) { 97 data = readl_relaxed(src); 98 memcpy(to, &data, len); 99 } 100 } 101 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

Hi Serge, Serge Semin <Sergey.Semin(a)baikalelectronics.ru&gt; 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?

Hi Sergey, Serge Semin <Sergey.Semin(a)baikalelectronics.ru&gt; 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&gt; 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?

On 11/12/20 1:57 PM, Miquel Raynal wrote: > Hi Sergey, > > Serge Semin <Sergey.Semin(a)baikalelectronics.ru&gt; 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&gt; 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;

Hi Serge, Serge Semin <Sergey.Semin(a)baikalelectronics.ru&gt; 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&gt; 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&gt; 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.

Hi Serge, Serge Semin <Sergey.Semin(a)baikalelectronics.ru&gt; wrote on Thu, 12 Nov 2020 19:10:43 +0300: > On Thu, Nov 12, 2020 at 04:43:01PM +0100, Miquel Raynal wrote: > > Hi Serge, > > > > Serge Semin <Sergey.Semin(a)baikalelectronics.ru&gt; 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&gt; 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&gt; 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?

I would say yes. > 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). Fine. > > 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. Yeah this is strange. I would, however, suggest not to add this keyword if we don't need it.