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

[Steffen Trumtrar <s.trumtrar@pengutronix.de>]

On Thu, Nov 22, 2012 at 10:07:07AM +0100, Laurent Pinchart wrote:
> On Thursday 22 November 2012 09:53:42 Sascha Hauer wrote:
> > On Thu, Nov 22, 2012 at 09:50:10AM +0100, Laurent Pinchart wrote:
> > > 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.
> 
> My bad, I though refresh was expressed in mHz. So yes, the above computation 
> is wrong.
>

Okay. I will fix that with the next version...

> BTW it seems that the refreshrate field in struct videomode isn't used. It 
> should then be removed.
> 

...and remove this field.

> I've just realized that the struct videomode fields are not documented. 
> kerneldoc in include/linux/videomode.h would be a good addition.
> 

Regards,
Steffen

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