Re: [PATCH] drm/drm_vblank.c: avoid unsigned int to signed int cast

[Sui Jingfeng]

Hi,

On 2023/5/23 16:50, David Laight wrote:
> From: 15330273260@xxxxxx <15330273260@xxxxxx>
> > 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 not 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.

It is about sign extend.

Yes, you may be right. I might create a wrong patch.

But this will not happen in practice, because in general case:

mode->crtc_htotal < 0x8fff;

mode->crtc_vtotal < 0x8fff;

u16 gets promoted to 'signed int' not 'unsigned int'.

Sorry  :/

> 	David
>
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