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

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:

quoted

Hi Steffen,

quoted

+
+	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 :-)

-- 
Regards,

Laurent Pinchart

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:

quoted

On Wed, Nov 21, 2012 at 11:02:44PM +0100, Laurent Pinchart wrote:

quoted

Hi Steffen,

quoted

+
+	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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