Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.37 as permitted sender) client-ip=23.128.96.37;
Message-ID: <5c5647d5-b389-4d71-9062-3a9921212079@ideasonboard.com>
Date:   Wed, 13 Dec 2023 13:40:54 +0200
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH] [v2] media: i2c: mt9m114: use fsleep() in place of
 udelay()
Content-Language: en-US
To:     Arnd Bergmann <arnd@kernel.org>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Sakari Ailus <sakari.ailus@linux.intel.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Jacopo Mondi <jacopo.mondi@ideasonboard.com>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Bill Wendling <morbo@google.com>,
        Justin Stitt <justinstitt@google.com>,
        Shuah Khan <skhan@linuxfoundation.org>,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        llvm@lists.linux.dev
References: <20231213112322.1655236-1-arnd@kernel.org>
From:   Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Autocrypt: addr=tomi.valkeinen@ideasonboard.com; keydata=
 xsFNBE6ms0cBEACyizowecZqXfMZtnBniOieTuFdErHAUyxVgtmr0f5ZfIi9Z4l+uUN4Zdw2
 wCEZjx3o0Z34diXBaMRJ3rAk9yB90UJAnLtb8A97Oq64DskLF81GCYB2P1i0qrG7UjpASgCA
 Ru0lVvxsWyIwSfoYoLrazbT1wkWRs8YBkkXQFfL7Mn3ZMoGPcpfwYH9O7bV1NslbmyJzRCMO
 eYV258gjCcwYlrkyIratlHCek4GrwV8Z9NQcjD5iLzrONjfafrWPwj6yn2RlL0mQEwt1lOvn
 LnI7QRtB3zxA3yB+FLsT1hx0va6xCHpX3QO2gBsyHCyVafFMrg3c/7IIWkDLngJxFgz6DLiA
 G4ld1QK/jsYqfP2GIMH1mFdjY+iagG4DqOsjip479HCWAptpNxSOCL6z3qxCU8MCz8iNOtZk
 DYXQWVscM5qgYSn+fmMM2qN+eoWlnCGVURZZLDjg387S2E1jT/dNTOsM/IqQj+ZROUZuRcF7
 0RTtuU5q1HnbRNwy+23xeoSGuwmLQ2UsUk7Q5CnrjYfiPo3wHze8avK95JBoSd+WIRmV3uoO
 rXCoYOIRlDhg9XJTrbnQ3Ot5zOa0Y9c4IpyAlut6mDtxtKXr4+8OzjSVFww7tIwadTK3wDQv
 Bus4jxHjS6dz1g2ypT65qnHen6mUUH63lhzewqO9peAHJ0SLrQARAQABzTBUb21pIFZhbGtl
 aW5lbiA8dG9taS52YWxrZWluZW5AaWRlYXNvbmJvYXJkLmNvbT7CwY4EEwEIADgWIQTEOAw+
 ll79gQef86f6PaqMvJYe9QUCX/HruAIbAwULCQgHAgYVCgkICwIEFgIDAQIeAQIXgAAKCRD6
 PaqMvJYe9WmFD/99NGoD5lBJhlFDHMZvO+Op8vCwnIRZdTsyrtGl72rVh9xRfcSgYPZUvBuT
 VDxE53mY9HaZyu1eGMccYRBaTLJSfCXl/g317CrMNdY0k40b9YeIX10feiRYEWoDIPQ3tMmA
 0nHDygzcnuPiPT68JYZ6tUOvAt7r6OX/litM+m2/E9mtp8xCoWOo/kYO4mOAIoMNvLB8vufi
 uBB4e/AvAjtny4ScuNV5c5q8MkfNIiOyag9QCiQ/JfoAqzXRjVb4VZG72AKaElwipiKCWEcU
 R4+Bu5Qbaxj7Cd36M/bI54OrbWWETJkVVSV1i0tghCd6HHyquTdFl7wYcz6cL1hn/6byVnD+
 sR3BLvSBHYp8WSwv0TCuf6tLiNgHAO1hWiQ1pOoXyMEsxZlgPXT+wb4dbNVunckwqFjGxRbl
 Rz7apFT/ZRwbazEzEzNyrBOfB55xdipG/2+SmFn0oMFqFOBEszXLQVslh64lI0CMJm2OYYe3
 PxHqYaztyeXsx13Bfnq9+bUynAQ4uW1P5DJ3OIRZWKmbQd/Me3Fq6TU57LsvwRgE0Le9PFQs
 dcP2071rMTpqTUteEgODJS4VDf4lXJfY91u32BJkiqM7/62Cqatcz5UWWHq5xeF03MIUTqdE
 qHWk3RJEoWHWQRzQfcx6Fn2fDAUKhAddvoopfcjAHfpAWJ+ENc7BTQROprNHARAAx0aat8GU
 hsusCLc4MIxOQwidecCTRc9Dz/7U2goUwhw2O5j9TPqLtp57VITmHILnvZf6q3QAho2QMQyE
 DDvHubrdtEoqaaSKxKkFie1uhWNNvXPhwkKLYieyL9m2JdU+b88HaDnpzdyTTR4uH7wk0bBa
 KbTSgIFDDe5lXInypewPO30TmYNkFSexnnM3n1PBCqiJXsJahE4ZQ+WnV5FbPUj8T2zXS2xk
 0LZ0+DwKmZ0ZDovvdEWRWrz3UzJ8DLHb7blPpGhmqj3ANXQXC7mb9qJ6J/VSl61GbxIO2Dwb
 xPNkHk8fwnxlUBCOyBti/uD2uSTgKHNdabhVm2dgFNVuS1y3bBHbI/qjC3J7rWE0WiaHWEqy
 UVPk8rsph4rqITsj2RiY70vEW0SKePrChvET7D8P1UPqmveBNNtSS7In+DdZ5kUqLV7rJnM9
 /4cwy+uZUt8cuCZlcA5u8IsBCNJudxEqBG10GHg1B6h1RZIz9Q9XfiBdaqa5+CjyFs8ua01c
 9HmyfkuhXG2OLjfQuK+Ygd56mV3lq0aFdwbaX16DG22c6flkkBSjyWXYepFtHz9KsBS0DaZb
 4IkLmZwEXpZcIOQjQ71fqlpiXkXSIaQ6YMEs8WjBbpP81h7QxWIfWtp+VnwNGc6nq5IQDESH
 mvQcsFS7d3eGVI6eyjCFdcAO8eMAEQEAAcLBXwQYAQIACQUCTqazRwIbDAAKCRD6PaqMvJYe
 9fA7EACS6exUedsBKmt4pT7nqXBcRsqm6YzT6DeCM8PWMTeaVGHiR4TnNFiT3otD5UpYQI7S
 suYxoTdHrrrBzdlKe5rUWpzoZkVK6p0s9OIvGzLT0lrb0HC9iNDWT3JgpYDnk4Z2mFi6tTbq
 xKMtpVFRA6FjviGDRsfkfoURZI51nf2RSAk/A8BEDDZ7lgJHskYoklSpwyrXhkp9FHGMaYII
 m9EKuUTX9JPDG2FTthCBrdsgWYPdJQvM+zscq09vFMQ9Fykbx5N8z/oFEUy3ACyPqW2oyfvU
 CH5WDpWBG0s5BALp1gBJPytIAd/pY/5ZdNoi0Cx3+Z7jaBFEyYJdWy1hGddpkgnMjyOfLI7B
 CFrdecTZbR5upjNSDvQ7RG85SnpYJTIin+SAUazAeA2nS6gTZzumgtdw8XmVXZwdBfF+ICof
 92UkbYcYNbzWO/GHgsNT1WnM4sa9lwCSWH8Fw1o/3bX1VVPEsnESOfxkNdu+gAF5S6+I6n3a
 ueeIlwJl5CpT5l8RpoZXEOVtXYn8zzOJ7oGZYINRV9Pf8qKGLf3Dft7zKBP832I3PQjeok7F
 yjt+9S+KgSFSHP3Pa4E7lsSdWhSlHYNdG/czhoUkSCN09C0rEK93wxACx3vtxPLjXu6RptBw
 3dRq7n+mQChEB1am0BueV1JZaBboIL0AGlSJkm23kw==
In-Reply-To: <20231213112322.1655236-1-arnd@kernel.org>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 13/12/2023 13:23, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.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.
> 
> Cc: Sakari Ailus <sakari.ailus@linux.intel.com>
> Fixes: 24d756e914fc ("media: i2c: Add driver for onsemi MT9M114 camera sensor")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>   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 {
>   		/*

I think this is fine, so:

Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>

But: If we don't have COMMON_CLK (or rather, I think, HAVE_CLK), the 
freq will be zero at compile time. So won't the compiler give a warning 
for the DIV_ROUND_UP() call?

Interestingly, for me, this doesn't give a div-by-zero warning:

	int x;
	int y = 0;
	x = DIV_ROUND_UP(10, y);

but this does:

	int x;
	const int y = 0;
	x = DIV_ROUND_UP(10, y);

And looks like this gives the warning too:

	int x;
	const int y = 0;
	if (y)
		x = DIV_ROUND_UP(10, y);

So, I think, the code in the driver could fail to compile at some later 
point, if the compiler warnings are improved (?), or if someone adds a 
'const' in front of 'long freq = clk_get_rate(sensor->clk);' line.

Maybe worry about that if it actually happens =).

  Tomi