linux-kernel - Re: [PATCH] leds: lm355x: avoid enum conversion warning

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Date:   Tue, 5 May 2020 19:44:16 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>, Bryan Wu <bryan.wu@...onical.com>,
        "G.Shark Jeong" <gshark.jeong@...il.com>,
        Dan Murphy <dmurphy@...com>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH] leds: lm355x: avoid enum conversion warning

On Tue, May 05, 2020 at 04:19:17PM +0200, Arnd Bergmann wrote:
> clang points out that doing arithmetic between diffent enums is usually
                                                 ^ different
> a mistake:
> 
> drivers/leds/leds-lm355x.c:167:28: warning: bitwise operation between different enumeration types ('enum lm355x_tx2' and 'enum lm355x_ntc') [-Wenum-enum-conversion]
>                 reg_val = pdata->pin_tx2 | pdata->ntc_pin;
>                           ~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~
> drivers/leds/leds-lm355x.c:178:28: warning: bitwise operation between different enumeration types ('enum lm355x_tx2' and 'enum lm355x_ntc') [-Wenum-enum-conversion]
>                 reg_val = pdata->pin_tx2 | pdata->ntc_pin | pdata->pass_mode;
>                           ~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~
> 
> In this driver, it is intentional, so add a cast to hide the false-positive

Not sure that I would call this a false positive. The warning is correct
that there is a bitwise operation between different enumeration types
but we do not care since we are just using the enumerated type for its
integer value in lieu of a #define VAR value.

> warning. It appears to be the only instance of this warning at the moment.
> 
> Fixes: b98d13c72592 ("leds: Add new LED driver for lm355x chips")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/leds/leds-lm355x.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/leds/leds-lm355x.c b/drivers/leds/leds-lm355x.c
> index 11ce05249751..b2eb2e1e9c04 100644
> --- a/drivers/leds/leds-lm355x.c
> +++ b/drivers/leds/leds-lm355x.c
> @@ -164,18 +164,19 @@ static int lm355x_chip_init(struct lm355x_chip_data *chip)
>  	/* input and output pins configuration */
>  	switch (chip->type) {
>  	case CHIP_LM3554:
> -		reg_val = pdata->pin_tx2 | pdata->ntc_pin;
> +		reg_val = (u32)pdata->pin_tx2 | (u32)pdata->ntc_pin;
>  		ret = regmap_update_bits(chip->regmap, 0xE0, 0x28, reg_val);
>  		if (ret < 0)
>  			goto out;
> -		reg_val = pdata->pass_mode;
> +		reg_val = (u32)pdata->pass_mode;

Is this cast needed? I don't think there should be warning from going
from an enumerated type to unsigned int.

>  		ret = regmap_update_bits(chip->regmap, 0xA0, 0x04, reg_val);
>  		if (ret < 0)
>  			goto out;
>  		break;
>  
>  	case CHIP_LM3556:
> -		reg_val = pdata->pin_tx2 | pdata->ntc_pin | pdata->pass_mode;
> +		reg_val = (u32)pdata->pin_tx2 | (u32)pdata->ntc_pin |
> +		          (u32)pdata->pass_mode;
>  		ret = regmap_update_bits(chip->regmap, 0x0A, 0xC4, reg_val);
>  		if (ret < 0)
>  			goto out;
> -- 
> 2.26.0
> 

With those comments addressed, feel free to add:

Reviewed-by: Nathan Chancellor <natechancellor@...il.com>