linux-kernel - Re: [PATCH v3 05/15] bus: ts-nbus: use bitmap_get

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Message-ID: <0084eef7-3831-4e62-acf1-6c2dc0e15dd1@baylibre.com>
Date: Thu, 20 Feb 2025 11:32:10 -0600
From: David Lechner <dlechner@...libre.com>
To: Simon Horman <horms@...nel.org>
Cc: Linus Walleij <linus.walleij@...aro.org>,
 Bartosz Golaszewski <brgl@...ev.pl>, Andy Shevchenko <andy@...nel.org>,
 Geert Uytterhoeven <geert@...ux-m68k.org>,
 Lars-Peter Clausen <lars@...afoo.de>,
 Michael Hennerich <Michael.Hennerich@...log.com>,
 Jonathan Cameron <jic23@...nel.org>, Ulf Hansson <ulf.hansson@...aro.org>,
 Peter Rosin <peda@...ntia.se>, Andrew Lunn <andrew@...n.ch>,
 Heiner Kallweit <hkallweit1@...il.com>, Russell King
 <linux@...linux.org.uk>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Vinod Koul <vkoul@...nel.org>,
 Kishon Vijay Abraham I <kishon@...nel.org>, Nuno Sá
 <nuno.sa@...log.com>, Liam Girdwood <lgirdwood@...il.com>,
 Mark Brown <broonie@...nel.org>, Jaroslav Kysela <perex@...ex.cz>,
 Takashi Iwai <tiwai@...e.com>, linux-gpio@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
 linux-mmc@...r.kernel.org, netdev@...r.kernel.org,
 linux-phy@...ts.infradead.org, linux-sound@...r.kernel.org,
 Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: [PATCH v3 05/15] bus: ts-nbus: use bitmap_get_value8()

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@...il.com>
> u> Signed-off-by: David Lechner <dlechner@...libre.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
>>