# Re: \[PATCH v12 3/6\] fbmon: add videomode helpers

- From: Sascha Hauer \<hidden\>
- Date: 2012-11-22 08:53:42 
- List: linux-devicetree
- Page: https://ratatoskr.run/linux-devicetree/2012/11/8065951
- Thread: https://ratatoskr.run/dri-devel/2012/11/8065950/t.md

```text
On Thu, Nov 22, 2012 at 09:50:10AM +0100, Laurent Pinchart wrote:
> Hi Sascha,
> 
> On Thursday 22 November 2012 07:20:00 Sascha Hauer wrote:
> > On Wed, Nov 21, 2012 at 11:02:44PM +0100, Laurent Pinchart wrote:
> > > Hi Steffen,
> > > 
> > > > +
> > > > +	htotal = vm->hactive + vm->hfront_porch + vm->hback_porch +
> > > > +		 vm->hsync_len;
> > > > +	vtotal = vm->vactive + vm->vfront_porch + vm->vback_porch +
> > > > +		 vm->vsync_len;
> > > > +	fbmode->refresh = (vm->pixelclock * 1000) / (htotal * vtotal);
> > > 
> > > This will fail if vm->pixelclock >= ((1 << 32) / 1000). The easiest
> > > solution is probably to use 64-bit computation.
> > 
> > You have displays with a pixelclock > 4GHz?
> 
> vm->pixelclock is expressed in Hz. vm->pixelclock * 1000 will thus overflow if 
> the clock frequency is >= ~4.3 MHz. I have displays with a clock frequency 
> higher than that :-)

If vm->pixelclock is in Hz, then the * 1000 above is wrong.

Sascha

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```