| Message ID | 20250210-gpio-set-array-helper-v3-5-d6a673674da8@baylibre.com |
|---|---|
| State | New |
| Headers | show |
| Series | gpiolib: add gpiod_multi_set_value_cansleep | expand |
On Mon, Feb 10, 2025 at 04:33:31PM -0600, David Lechner wrote: > Use bitmap_get_value8() instead of accessing the bitmap directly. > > Accessing the bitmap directly is not considered good practice. We now > have a helper function that can be used instead, so let's use it. > > Suggested-by: Andy Shevchenko <andy.shevchenko@gmail.com> u> Signed-off-by: David Lechner <dlechner@baylibre.com> > --- > drivers/bus/ts-nbus.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/drivers/bus/ts-nbus.c b/drivers/bus/ts-nbus.c > index b4c9308caf0647a3261071d9527fffce77784af2..beac67f3b820377f8bb1fc4f4ee77e15ee240834 100644 > --- a/drivers/bus/ts-nbus.c > +++ b/drivers/bus/ts-nbus.c > @@ -10,6 +10,7 @@ > * TS-4600 SoM. > */ > > +#include <linux/bitmap.h> > #include <linux/bitops.h> > #include <linux/gpio/consumer.h> > #include <linux/kernel.h> > @@ -107,7 +108,7 @@ static void ts_nbus_reset_bus(struct ts_nbus *ts_nbus) > { > DECLARE_BITMAP(values, 8); > > - values[0] = 0; > + bitmap_set_value8(values, byte, 0); Hi David, byte doesn't appear to exist in the scope of this function. I tried this: bitmap_set_value8(values, 0, 8); But when compiling with GCC 14.2.0 I see warnings that values is used uninitialised - bitmap_set_value8() appears to rely on it being so. CC drivers/bus/ts-nbus.o In file included from drivers/bus/ts-nbus.c:13: In function ‘bitmap_write’, inlined from ‘ts_nbus_reset_bus’ at drivers/bus/ts-nbus.c:111:2: ./include/linux/bitmap.h:818:12: error: ‘values’ is used uninitialized [-Werror=uninitialized] 818 | map[index] &= (fit ? (~(mask << offset)) : ~BITMAP_FIRST_WORD_MASK(start)); | ~~~^~~~~~~ In file included from ./include/linux/kasan-checks.h:5, from ./include/asm-generic/rwonce.h:26, from ./arch/x86/include/generated/asm/rwonce.h:1, from ./include/linux/compiler.h:344, from ./include/linux/build_bug.h:5, from ./include/linux/bits.h:22, from ./include/linux/bitops.h:6, from ./include/linux/bitmap.h:8: drivers/bus/ts-nbus.c: In function ‘ts_nbus_reset_bus’: drivers/bus/ts-nbus.c:109:24: note: ‘values’ declared here 109 | DECLARE_BITMAP(values, 8); | ^~~~~~ ./include/linux/types.h:11:23: note: in definition of macro ‘DECLARE_BITMAP’ 11 | unsigned long name[BITS_TO_LONGS(bits)] | ^~~~ > > gpiod_multi_set_value_cansleep(ts_nbus->data, values); > gpiod_set_value_cansleep(ts_nbus->csn, 0); > @@ -151,7 +152,7 @@ static void ts_nbus_write_byte(struct ts_nbus *ts_nbus, u8 byte) > { > DECLARE_BITMAP(values, 8); > > - values[0] = byte; > + bitmap_set_value8(values, byte, 8); > > gpiod_multi_set_value_cansleep(ts_nbus->data, values); > } > > -- > 2.43.0 >
On Thu, Feb 20, 2025 at 12:17 PM Simon Horman <horms@kernel.org> wrote: > On Mon, Feb 10, 2025 at 04:33:31PM -0600, David Lechner wrote: ... > But when compiling with GCC 14.2.0 I see warnings that values > is used uninitialised - bitmap_set_value8() appears to rely on > it being so. > In file included from drivers/bus/ts-nbus.c:13: > In function ‘bitmap_write’, > inlined from ‘ts_nbus_reset_bus’ at drivers/bus/ts-nbus.c:111:2: > ./include/linux/bitmap.h:818:12: error: ‘values’ is used uninitialized [-Werror=uninitialized] > 818 | map[index] &= (fit ? (~(mask << offset)) : ~BITMAP_FIRST_WORD_MASK(start)); > | ~~~^~~~~~~ Heh, the compiler is dumb. Even if it's not initialised we do not care. ... Wondering if the bitmap_write() will work better...
On 2/20/25 6:06 AM, Andy Shevchenko wrote: > On Thu, Feb 20, 2025 at 12:17 PM Simon Horman <horms@kernel.org> wrote: >> On Mon, Feb 10, 2025 at 04:33:31PM -0600, David Lechner wrote: > > ... > >> But when compiling with GCC 14.2.0 I see warnings that values >> is used uninitialised - bitmap_set_value8() appears to rely on >> it being so. > >> In file included from drivers/bus/ts-nbus.c:13: >> In function ‘bitmap_write’, >> inlined from ‘ts_nbus_reset_bus’ at drivers/bus/ts-nbus.c:111:2: >> ./include/linux/bitmap.h:818:12: error: ‘values’ is used uninitialized [-Werror=uninitialized] >> 818 | map[index] &= (fit ? (~(mask << offset)) : ~BITMAP_FIRST_WORD_MASK(start)); >> | ~~~^~~~~~~ > > Heh, the compiler is dumb. Even if it's not initialised we do not care. > > ... > > Wondering if the bitmap_write() will work better... > It is already using that: #define bitmap_set_value8(map, value, start) \ bitmap_write(map, value, start, BITS_PER_BYTE)
On 2/20/25 4:17 AM, Simon Horman wrote: > On Mon, Feb 10, 2025 at 04:33:31PM -0600, David Lechner wrote: >> Use bitmap_get_value8() instead of accessing the bitmap directly. >> >> Accessing the bitmap directly is not considered good practice. We now >> have a helper function that can be used instead, so let's use it. >> >> Suggested-by: Andy Shevchenko <andy.shevchenko@gmail.com> > u> Signed-off-by: David Lechner <dlechner@baylibre.com> >> --- >> drivers/bus/ts-nbus.c | 5 +++-- >> 1 file changed, 3 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/bus/ts-nbus.c b/drivers/bus/ts-nbus.c >> index b4c9308caf0647a3261071d9527fffce77784af2..beac67f3b820377f8bb1fc4f4ee77e15ee240834 100644 >> --- a/drivers/bus/ts-nbus.c >> +++ b/drivers/bus/ts-nbus.c >> @@ -10,6 +10,7 @@ >> * TS-4600 SoM. >> */ >> >> +#include <linux/bitmap.h> >> #include <linux/bitops.h> >> #include <linux/gpio/consumer.h> >> #include <linux/kernel.h> >> @@ -107,7 +108,7 @@ static void ts_nbus_reset_bus(struct ts_nbus *ts_nbus) >> { >> DECLARE_BITMAP(values, 8); >> >> - values[0] = 0; >> + bitmap_set_value8(values, byte, 0); > > Hi David, > > byte doesn't appear to exist in the scope of this function. > > I tried this: > > bitmap_set_value8(values, 0, 8); > > But when compiling with GCC 14.2.0 I see warnings that values > is used uninitialised - bitmap_set_value8() appears to rely on > it being so. Ah yes, I see the problem (I don't think this driver compiles with allmodconfig so the compiler didn't catch it for me). > > CC drivers/bus/ts-nbus.o > In file included from drivers/bus/ts-nbus.c:13: > In function ‘bitmap_write’, > inlined from ‘ts_nbus_reset_bus’ at drivers/bus/ts-nbus.c:111:2: > ./include/linux/bitmap.h:818:12: error: ‘values’ is used uninitialized [-Werror=uninitialized] > 818 | map[index] &= (fit ? (~(mask << offset)) : ~BITMAP_FIRST_WORD_MASK(start)); > | ~~~^~~~~~~ > In file included from ./include/linux/kasan-checks.h:5, > from ./include/asm-generic/rwonce.h:26, > from ./arch/x86/include/generated/asm/rwonce.h:1, > from ./include/linux/compiler.h:344, > from ./include/linux/build_bug.h:5, > from ./include/linux/bits.h:22, > from ./include/linux/bitops.h:6, > from ./include/linux/bitmap.h:8: > drivers/bus/ts-nbus.c: In function ‘ts_nbus_reset_bus’: > drivers/bus/ts-nbus.c:109:24: note: ‘values’ declared here > 109 | DECLARE_BITMAP(values, 8); > | ^~~~~~ > ./include/linux/types.h:11:23: note: in definition of macro ‘DECLARE_BITMAP’ > 11 | unsigned long name[BITS_TO_LONGS(bits)] > | ^~~~ > > >> >> gpiod_multi_set_value_cansleep(ts_nbus->data, values); >> gpiod_set_value_cansleep(ts_nbus->csn, 0); >> @@ -151,7 +152,7 @@ static void ts_nbus_write_byte(struct ts_nbus *ts_nbus, u8 byte) >> { >> DECLARE_BITMAP(values, 8); We can fix by zero-initialing the bitmap. DECLARE_BITMAP(values, 8) = { }; Would you like me to send a new version of the patch? >> >> - values[0] = byte; >> + bitmap_set_value8(values, byte, 8); >> >> gpiod_multi_set_value_cansleep(ts_nbus->data, values); >> } >> >> -- >> 2.43.0 >>
On Thu, Feb 20, 2025 at 11:32:10AM -0600, David Lechner wrote: > On 2/20/25 4:17 AM, Simon Horman wrote: > > On Mon, Feb 10, 2025 at 04:33:31PM -0600, David Lechner wrote: > >> Use bitmap_get_value8() instead of accessing the bitmap directly. > >> > >> Accessing the bitmap directly is not considered good practice. We now > >> have a helper function that can be used instead, so let's use it. > >> > >> Suggested-by: Andy Shevchenko <andy.shevchenko@gmail.com> > > u> Signed-off-by: David Lechner <dlechner@baylibre.com> > >> --- > >> drivers/bus/ts-nbus.c | 5 +++-- > >> 1 file changed, 3 insertions(+), 2 deletions(-) > >> > >> diff --git a/drivers/bus/ts-nbus.c b/drivers/bus/ts-nbus.c > >> index b4c9308caf0647a3261071d9527fffce77784af2..beac67f3b820377f8bb1fc4f4ee77e15ee240834 100644 > >> --- a/drivers/bus/ts-nbus.c > >> +++ b/drivers/bus/ts-nbus.c > >> @@ -10,6 +10,7 @@ > >> * TS-4600 SoM. > >> */ > >> > >> +#include <linux/bitmap.h> > >> #include <linux/bitops.h> > >> #include <linux/gpio/consumer.h> > >> #include <linux/kernel.h> > >> @@ -107,7 +108,7 @@ static void ts_nbus_reset_bus(struct ts_nbus *ts_nbus) > >> { > >> DECLARE_BITMAP(values, 8); > >> > >> - values[0] = 0; > >> + bitmap_set_value8(values, byte, 0); > > > > Hi David, > > > > byte doesn't appear to exist in the scope of this function. > > > > I tried this: > > > > bitmap_set_value8(values, 0, 8); > > > > But when compiling with GCC 14.2.0 I see warnings that values > > is used uninitialised - bitmap_set_value8() appears to rely on > > it being so. > > Ah yes, I see the problem (I don't think this driver compiles with > allmodconfig so the compiler didn't catch it for me). Thanks, that would explain things. FWIIW, I think you can exercise this with allmodconfig by simply running: make drivers/bus/ts-nbus.o > > > > > CC drivers/bus/ts-nbus.o > > In file included from drivers/bus/ts-nbus.c:13: > > In function ‘bitmap_write’, > > inlined from ‘ts_nbus_reset_bus’ at drivers/bus/ts-nbus.c:111:2: > > ./include/linux/bitmap.h:818:12: error: ‘values’ is used uninitialized [-Werror=uninitialized] > > 818 | map[index] &= (fit ? (~(mask << offset)) : ~BITMAP_FIRST_WORD_MASK(start)); > > | ~~~^~~~~~~ > > In file included from ./include/linux/kasan-checks.h:5, > > from ./include/asm-generic/rwonce.h:26, > > from ./arch/x86/include/generated/asm/rwonce.h:1, > > from ./include/linux/compiler.h:344, > > from ./include/linux/build_bug.h:5, > > from ./include/linux/bits.h:22, > > from ./include/linux/bitops.h:6, > > from ./include/linux/bitmap.h:8: > > drivers/bus/ts-nbus.c: In function ‘ts_nbus_reset_bus’: > > drivers/bus/ts-nbus.c:109:24: note: ‘values’ declared here > > 109 | DECLARE_BITMAP(values, 8); > > | ^~~~~~ > > ./include/linux/types.h:11:23: note: in definition of macro ‘DECLARE_BITMAP’ > > 11 | unsigned long name[BITS_TO_LONGS(bits)] > > | ^~~~ > > > > > >> > >> gpiod_multi_set_value_cansleep(ts_nbus->data, values); > >> gpiod_set_value_cansleep(ts_nbus->csn, 0); > >> @@ -151,7 +152,7 @@ static void ts_nbus_write_byte(struct ts_nbus *ts_nbus, u8 byte) > >> { > >> DECLARE_BITMAP(values, 8); > > We can fix by zero-initialing the bitmap. > > DECLARE_BITMAP(values, 8) = { }; Thanks, I confirmed that adding that to ts_nbus_reset_bus() makes the compiler happy. And it seems sensible to me. I guess that theoretically it should also be added to ts_nbus_write_byte(), although GCC has nothing to say about that either way. > Would you like me to send a new version of the patch? It's not really my call. But I would expect that is a good next step. > >> - values[0] = byte; > >> + bitmap_set_value8(values, byte, 8); > >> > >> gpiod_multi_set_value_cansleep(ts_nbus->data, values); > >> }
diff --git a/drivers/bus/ts-nbus.c b/drivers/bus/ts-nbus.c index b4c9308caf0647a3261071d9527fffce77784af2..beac67f3b820377f8bb1fc4f4ee77e15ee240834 100644 --- a/drivers/bus/ts-nbus.c +++ b/drivers/bus/ts-nbus.c @@ -10,6 +10,7 @@ * TS-4600 SoM. */ +#include <linux/bitmap.h> #include <linux/bitops.h> #include <linux/gpio/consumer.h> #include <linux/kernel.h> @@ -107,7 +108,7 @@ static void ts_nbus_reset_bus(struct ts_nbus *ts_nbus) { DECLARE_BITMAP(values, 8); - values[0] = 0; + bitmap_set_value8(values, byte, 0); gpiod_multi_set_value_cansleep(ts_nbus->data, values); gpiod_set_value_cansleep(ts_nbus->csn, 0); @@ -151,7 +152,7 @@ static void ts_nbus_write_byte(struct ts_nbus *ts_nbus, u8 byte) { DECLARE_BITMAP(values, 8); - values[0] = byte; + bitmap_set_value8(values, byte, 8); gpiod_multi_set_value_cansleep(ts_nbus->data, values); }
Use bitmap_get_value8() instead of accessing the bitmap directly. Accessing the bitmap directly is not considered good practice. We now have a helper function that can be used instead, so let's use it. Suggested-by: Andy Shevchenko <andy.shevchenko@gmail.com> Signed-off-by: David Lechner <dlechner@baylibre.com> --- drivers/bus/ts-nbus.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)