Re: [PATCH 1/2] OMAPDSS: DISPC: Enable predecimation

["Ville Syrjälä" <syrjala@sci.fi>]

On Thu, Mar 15, 2012 at 05:18:28PM +0530, Chandrabhanu Mahapatra wrote:
> In OMAP3 and OMAP4, the DISPC Scaler can downscale an image up to 4 times, and
> up to 2 times in OMAP2. However, with predecimation, the image can be reduced
> to 16 times by fetching only the necessary pixels in memory. Then this
> predecimated image can be downscaled further by the DISPC scaler.

Now, where does that number 16 come from? IIRC the hardware can skip
basically any number of pixels/rows. I certainly didn't add any such
limit to the code in the harmattan kernel, and distinctly remember
being able to downscale the N9/N950 UI even down to 1 pixel size :)

> Based on the downscaling required, a prior calculation of predecimation values
> for width and height of an image is done. Since, Predecimation reduces quality
> of an image higher priorty is given to DISPC Scaler for downscaling.
> 
> This code was successfully tested on OMAP2, OMAP3 and OMAP4. Horizontal and
> vertical predecimation worked fine except for some synclost errors due to
> undocumented errata in OMAP3 which are fixed later and skewed images were seen
> on OMAP2 and OMAP3 during horizontal predecimation which will be addressed in
> the future patches.

All the rotation offset calculations still look suspiciously different
to what is in the harmattan kernel. I remember that the original code
was quite broken, and I fixed a lot of things when I was implementing
pre-decimation and some rotation stuff for the N9/N950. Too bad I never
managed to push that stuff upstream...

-- 
Ville Syrjälä
syrjala@sci.fi
http://www.sci.fi/~syrjala/