From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="Hwp6d+Ej" Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [213.167.242.64]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4CCFFCD; Wed, 13 Dec 2023 04:09:03 -0800 (PST) Received: from pendragon.ideasonboard.com (213-243-189-158.bb.dnainternet.fi [213.243.189.158]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 2BC6666F; Wed, 13 Dec 2023 13:08:16 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1702469296; bh=jqhRjEL97tn66XG6waeuYNlSKAzpHyL1g4+7ALb8P6Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Hwp6d+EjAYB0geF68t4m6zgcSbUiP+a93h4cqFqIC3Vzcbm2w9XuqWaArOoceoFlp ISYe3zCw05UnSJi4G81SOMUr8xC/qfJqhBMNag4gvwnMMiO5gQbVLGBxIIIGSs537k HKFJpw8ki6RmYvuiLZW89YKvP8LMgmmqd1+lIOVc= Date: Wed, 13 Dec 2023 14:09:09 +0200 From: Laurent Pinchart To: Tomi Valkeinen Cc: Arnd Bergmann , Sakari Ailus , Mauro Carvalho Chehab , Nathan Chancellor , Jacopo Mondi , Hans Verkuil , Arnd Bergmann , Nick Desaulniers , Bill Wendling , Justin Stitt , Shuah Khan , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev Subject: Re: [PATCH] [v2] media: i2c: mt9m114: use fsleep() in place of udelay() Message-ID: <20231213120909.GC769@pendragon.ideasonboard.com> References: <20231213112322.1655236-1-arnd@kernel.org> <5c5647d5-b389-4d71-9062-3a9921212079@ideasonboard.com> <20231213114812.GB769@pendragon.ideasonboard.com> <0722393c-8107-4a8f-b3ab-1bbb347a6f1b@ideasonboard.com> Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <0722393c-8107-4a8f-b3ab-1bbb347a6f1b@ideasonboard.com> On Wed, Dec 13, 2023 at 01:56:48PM +0200, Tomi Valkeinen wrote: > On 13/12/2023 13:48, Laurent Pinchart wrote: > > On Wed, Dec 13, 2023 at 01:40:54PM +0200, Tomi Valkeinen wrote: > >> On 13/12/2023 13:23, Arnd Bergmann wrote: > >>> From: Arnd Bergmann > >>> > >>> 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 > >>> Fixes: 24d756e914fc ("media: i2c: Add driver for onsemi MT9M114 camera sensor") > >>> Signed-off-by: Arnd Bergmann > >>> --- > >>> 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 > >> > >> 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 =). > > > > Maybe :-) I would be tempted to make VIDEO_CAMERA_SENSOR depend on > > COMMON_CLK. > > I think HAVE_CLK would be more correct. Indeed. Only arch/m68k (for Coldfire), arch/mips (for BCM63xx and Lantiq) and arch/sh (for pre-DT platforms) still make use of HAVE_LEGACY_CLK. It takes a long time to address the last users of a legacy API, but it seems we could get there one day. -- Regards, Laurent Pinchart