linux-kernel - Re: [PATCH] [v2] media: i2c: mt9m114: use fsleep() in place of udelay()

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Message-ID: <20231213113645.GA769@pendragon.ideasonboard.com>
Date:   Wed, 13 Dec 2023 13:36:45 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Jacopo Mondi <jacopo.mondi@...asonboard.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Arnd Bergmann <arnd@...db.de>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Bill Wendling <morbo@...gle.com>,
        Justin Stitt <justinstitt@...gle.com>,
        Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
        Shuah Khan <skhan@...uxfoundation.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH] [v2] media: i2c: mt9m114: use fsleep() in place of
 udelay()

Hi Arnd,

Thank you for the patch.

On Wed, Dec 13, 2023 at 12:23:07PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> With clang-16, building without COMMON_CLK triggers a range check on
> udelay() because of a constant division-by-zero calculation:
> 
> ld.lld: error: undefined symbol: __bad_udelay
> >>> referenced by mt9m114.c
> >>>               drivers/media/i2c/mt9m114.o:(mt9m114_power_on) in archive vmlinux.a
> 
> In this configuration, the driver already fails to probe, before
> this function gets called, so it's enough to suppress the assertion.
> 
> Do this by using fsleep(), which turns long delays into sleep() calls
> in place of the link failure.
> 
> This is probably a good idea regardless to avoid overly long dynamic
> udelay() calls on a slow clock.

The longest delay would be 16.66µs, which may not be worth a sleep, but
I think that's fine. Using fsleep() by default is a good idea.

> Cc: Sakari Ailus <sakari.ailus@...ux.intel.com>
> Fixes: 24d756e914fc ("media: i2c: Add driver for onsemi MT9M114 camera sensor")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

>  drivers/media/i2c/mt9m114.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/media/i2c/mt9m114.c b/drivers/media/i2c/mt9m114.c
> index 0a22f328981d..68adaecaf481 100644
> --- a/drivers/media/i2c/mt9m114.c
> +++ b/drivers/media/i2c/mt9m114.c
> @@ -2116,7 +2116,7 @@ static int mt9m114_power_on(struct mt9m114 *sensor)
>  		duration = DIV_ROUND_UP(2 * 50 * 1000000, freq);
>  
>  		gpiod_set_value(sensor->reset, 1);
> -		udelay(duration);
> +		fsleep(duration);
>  		gpiod_set_value(sensor->reset, 0);
>  	} else {
>  		/*

-- 
Regards,

Laurent Pinchart