Subject: Re: [PATCH v3 05/15] bus: ts-nbus: use bitmap_get_value8()

From: Simon Horman <[email-masked]>
Date: Thu, 20 Feb 2025 10:17:42 +0000

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 <[email-masked]>
u> Signed-off-by: David Lechner <[email-masked]>
> ---
>  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
>