linux-kernel - RE: [PATCH] drm/drm_vblank.c: avoid unsigned int to signed int cast

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Message-ID: <e5effc4568034489acf2f4d4dad6eba9@AcuMS.aculab.com>
Date:   Tue, 23 May 2023 08:50:30 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'15330273260@....cn'" <15330273260@....cn>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Sui Jingfeng <suijingfeng@...ngson.cn>,
        Li Yi <liyi@...ngson.cn>
CC:     Thomas Zimmermann <tzimmermann@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "loongson-kernel@...ts.loongnix.cn" 
        <loongson-kernel@...ts.loongnix.cn>
Subject: RE: [PATCH] drm/drm_vblank.c: avoid unsigned int to signed int cast

From: 15330273260@....cn <15330273260@....cn>
> Sent: 23 May 2023 05:27
> 
> On 2023/5/22 19:29, Jani Nikula wrote:
> > In general, do not use unsigned types in arithmethic to avoid negative
> > values, because most people will be tripped over by integer promotion
> > rules, and you'll get negative values anyway.
> 
> 
> Here I'm sure about this,
> 
> but there are plenty unsigned types arithmetic in the kernel.

The real problem is (attempted) arithmetic on types smaller than int.
Regardless of whether they are signed or unsigned.

	David

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