[PATCH] leds: sun50i-a100: avoid division-by-zero warning

[PATCH] leds: sun50i-a100: avoid division-by-zero warning

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

When CONFIG_COMMON_CLK is disabled, e.g. on an x86 randconfig compile test,
clang reports a field overflow from propagating the result of a division by
zero:

drivers/leds/leds-sun50i-a100.c:309:12: error: call to '__compiletime_assert_265' declared with 'error' attribute: FIELD_PREP: value too large for the field
        control = FIELD_PREP(LEDC_T01_TIMING_CTRL_REG_T1H, timing->t1h_ns / cycle_ns) |

Avoid the problem by adding an explicit check for the zero value here. Alternatively
the assertion could be avoided with a Kconfig dependency on COMMON_CLK.

Fixes: 090a25ad9798 ("leds: sun50i-a100: New driver for the A100 LED controller")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/leds/leds-sun50i-a100.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/leds/leds-sun50i-a100.c b/drivers/leds/leds-sun50i-a100.c
index e4a7e692a908..171cefd1ea0d 100644
--- a/drivers/leds/leds-sun50i-a100.c
+++ b/drivers/leds/leds-sun50i-a100.c
@@ -303,9 +303,13 @@ static void sun50i_a100_ledc_set_timing(struct sun50i_a100_ledc *priv)
 {
 	const struct sun50i_a100_ledc_timing *timing = &priv->timing;
 	unsigned long mod_freq = clk_get_rate(priv->mod_clk);
-	u32 cycle_ns = NSEC_PER_SEC / mod_freq;
+	u32 cycle_ns;
 	u32 control;
 
+	if (!mod_freq)
+		return;
+
+	cycle_ns = NSEC_PER_SEC / mod_freq;
 	control = FIELD_PREP(LEDC_T01_TIMING_CTRL_REG_T1H, timing->t1h_ns / cycle_ns) |
 		  FIELD_PREP(LEDC_T01_TIMING_CTRL_REG_T1L, timing->t1l_ns / cycle_ns) |
 		  FIELD_PREP(LEDC_T01_TIMING_CTRL_REG_T0H, timing->t0h_ns / cycle_ns) |
-- 
2.39.2

Re: [PATCH] leds: sun50i-a100: avoid division-by-zero warning

[Guo Ren]

On Wed, Dec 13, 2023 at 5:45 AM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> When CONFIG_COMMON_CLK is disabled, e.g. on an x86 randconfig compile test,
> clang reports a field overflow from propagating the result of a division by
> zero:
>
> drivers/leds/leds-sun50i-a100.c:309:12: error: call to '__compiletime_assert_265' declared with 'error' attribute: FIELD_PREP: value too large for the field
>         control = FIELD_PREP(LEDC_T01_TIMING_CTRL_REG_T1H, timing->t1h_ns / cycle_ns) |
>
> Avoid the problem by adding an explicit check for the zero value here. Alternatively
> the assertion could be avoided with a Kconfig dependency on COMMON_CLK.
>
> Fixes: 090a25ad9798 ("leds: sun50i-a100: New driver for the A100 LED controller")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/leds/leds-sun50i-a100.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/leds/leds-sun50i-a100.c b/drivers/leds/leds-sun50i-a100.c
> index e4a7e692a908..171cefd1ea0d 100644
> --- a/drivers/leds/leds-sun50i-a100.c
> +++ b/drivers/leds/leds-sun50i-a100.c
> @@ -303,9 +303,13 @@ static void sun50i_a100_ledc_set_timing(struct sun50i_a100_ledc *priv)
>  {
>         const struct sun50i_a100_ledc_timing *timing = &priv->timing;
>         unsigned long mod_freq = clk_get_rate(priv->mod_clk);
> -       u32 cycle_ns = NSEC_PER_SEC / mod_freq;
> +       u32 cycle_ns;
>         u32 control;
>
> +       if (!mod_freq)
> +               return;
> +
Shall we need err_disable_bus_clk?

+ static int sun50i_a100_ledc_set_timing(struct sun50i_a100_ledc *priv)
- static void sun50i_a100_ledc_set_timing(struct sun50i_a100_ledc *priv)
 {
         const struct sun50i_a100_ledc_timing *timing = &priv->timing;
         unsigned long mod_freq = clk_get_rate(priv->mod_clk);
 -       u32 cycle_ns = NSEC_PER_SEC / mod_freq;
 +       u32 cycle_ns;
         u32 control;

+       if (!mod_freq)
+               return -EINVAL;

 +       cycle_ns = NSEC_PER_SEC / mod_freq;
         control = FIELD_PREP(LEDC_T01_TIMING_CTRL_REG_T1H,
timing->t1h_ns / cycle_ns) |
                   FIELD_PREP(LEDC_T01_TIMING_CTRL_REG_T1L,
timing->t1l_ns / cycle_ns) |
                   FIELD_PREP(LEDC_T01_TIMING_CTRL_REG_T0H,
timing->t0h_ns / cycle_ns) |
...
       return 0;

----------

+ ret = sun50i_a100_ledc_set_timing(priv);
+ if (ret)
+         goto err_disable_bus_clk;



> --
> 2.39.2
>


-- 
Best Regards
 Guo Ren

Re: [PATCH] leds: sun50i-a100: avoid division-by-zero warning

[Arnd Bergmann]

On Wed, Dec 13, 2023, at 02:26, Guo Ren wrote:
> On Wed, Dec 13, 2023 at 5:45 AM Arnd Bergmann <arnd@kernel.org> wrote:
>>  {
>>         const struct sun50i_a100_ledc_timing *timing = &priv->timing;
>>         unsigned long mod_freq = clk_get_rate(priv->mod_clk);
>> -       u32 cycle_ns = NSEC_PER_SEC / mod_freq;
>> +       u32 cycle_ns;
>>         u32 control;
>>
>> +       if (!mod_freq)
>> +               return;
>> +
> Shall we need err_disable_bus_clk?
>
> + static int sun50i_a100_ledc_set_timing(struct sun50i_a100_ledc *priv)
> - static void sun50i_a100_ledc_set_timing(struct sun50i_a100_ledc *priv)

I'm not worried about it too much, as there is already an error check
on priv->mod_clk being unavailable during initialization. The case that
the warning is about is just for build-testing on architectures that
don't even use COMMON_CLK.

     Arnd

Re: [PATCH] leds: sun50i-a100: avoid division-by-zero warning

[Guo Ren]

On Wed, Dec 13, 2023 at 2:32 PM Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Wed, Dec 13, 2023, at 02:26, Guo Ren wrote:
> > On Wed, Dec 13, 2023 at 5:45 AM Arnd Bergmann <arnd@kernel.org> wrote:
> >>  {
> >>         const struct sun50i_a100_ledc_timing *timing = &priv->timing;
> >>         unsigned long mod_freq = clk_get_rate(priv->mod_clk);
> >> -       u32 cycle_ns = NSEC_PER_SEC / mod_freq;
> >> +       u32 cycle_ns;
> >>         u32 control;
> >>
> >> +       if (!mod_freq)
> >> +               return;
> >> +
> > Shall we need err_disable_bus_clk?
> >
> > + static int sun50i_a100_ledc_set_timing(struct sun50i_a100_ledc *priv)
> > - static void sun50i_a100_ledc_set_timing(struct sun50i_a100_ledc *priv)
>
> I'm not worried about it too much, as there is already an error check
> on priv->mod_clk being unavailable during initialization. The case that
> the warning is about is just for build-testing on architectures that
> don't even use COMMON_CLK.
Okay

Reviewed-by: Guo Ren <guoren@kernel.org>

>
>      Arnd



-- 
Best Regards
 Guo Ren

Re: (subset) [PATCH] leds: sun50i-a100: avoid division-by-zero warning

[Lee Jones]

On Tue, 12 Dec 2023 22:45:22 +0100, Arnd Bergmann wrote:
> When CONFIG_COMMON_CLK is disabled, e.g. on an x86 randconfig compile test,
> clang reports a field overflow from propagating the result of a division by
> zero:
> 
> drivers/leds/leds-sun50i-a100.c:309:12: error: call to '__compiletime_assert_265' declared with 'error' attribute: FIELD_PREP: value too large for the field
>         control = FIELD_PREP(LEDC_T01_TIMING_CTRL_REG_T1H, timing->t1h_ns / cycle_ns) |
> 
> [...]

Applied, thanks!

[1/1] leds: sun50i-a100: avoid division-by-zero warning
      commit: f969d75a0218da32c40dd4940bd430b0530433cf

--
Lee Jones [李琼斯]