Created attachment 25369 [details]
Output of lspci -vvnn

Created attachment 25370 [details]
Output of lspci -vvnn

The driver does do bilinear filtering between the texels.  We don't do doubling of the texels, since we don't convert planar to packed.

Do you have a specific proposal of how to improve the situation?

Unfortunately I don't have much knowledge in programming or driver development. But I know there is a similar issue with the ATI Catalyst driver on Windows, as you can see with this link: http://forum.doom9.org/showthread.php?t=141066 , and someone created a shader for Media Player Classic HC to correct the problem via point resize:
"
/*
YV12 chroma upsampling fixer
by Kurt Bernhard 'Leak' Pruenner

Use with YV12 output if the half-resolution chroma 
gets upsampled in hardware by doubling the values
instead of interpolating between them.

(i.e. if you're getting blocky red edges on dark 
backgrounds...)
*/

sampler s0 : register(s0);
float4 p0 : register(c0);
float4 p1 : register(c1);

#define width (p0[0])
#define height (p0[1])

float4 getPixel(float2 tex, float dx, float dy)
{
	tex.x+=dx;
	tex.y+=dy;
	
	return tex2D(s0, tex);
}

float4 rgb2yuv(float4 rgb)
{
	float4x4 coeffs=
		{
			 0.299, 0.587, 0.114, 0.000,
			-0.147,-0.289, 0.436, 0.000,
			 0.615,-0.515,-0.100, 0.000,
			 0.000, 0.000, 0.000, 0.000
		};
		
	return mul(coeffs,rgb);
}

float4 yuv2rgb(float4 yuv)
{
	float4x4 coeffs=
		{
			 1.000, 0.000, 1.140, 0.000,
			 1.000,-0.395,-0.581, 0.000,
			 1.000, 2.032, 0.000, 0.000,
			 0.000, 0.000, 0.000, 0.000
		};
	
	return mul(coeffs,yuv);
}

float4 main(float2 tex : TEXCOORD0) : COLOR
{
	float dx=1/width;
	float dy=1/height;
	
	float4 yuv00=rgb2yuv(getPixel(tex,-dx,-dy));
	float4 yuv01=rgb2yuv(getPixel(tex,-dx,  0));
	float4 yuv02=rgb2yuv(getPixel(tex,-dx, dy));
	float4 yuv10=rgb2yuv(getPixel(tex,  0,-dy));
	float4 yuv11=rgb2yuv(getPixel(tex,  0,  0));
	float4 yuv12=rgb2yuv(getPixel(tex,  0, dy));
	float4 yuv20=rgb2yuv(getPixel(tex, dx,-dy));
	float4 yuv21=rgb2yuv(getPixel(tex, dx,  0));
	float4 yuv22=rgb2yuv(getPixel(tex, dx, dy));

	float4 yuv=
		(yuv00*1+yuv01*2+yuv02*1+
		 yuv10*2+yuv11*4+yuv12*2+
		 yuv20*1+yuv21*2+yuv22*1)/16;
	
	yuv.r=yuv11.r;

	return yuv2rgb(yuv);
}

"

Here is a description of what it does "What it does is actually quite dumb - it takes each pixel from the (blocky) RGB image the shader gets fed as well as the ones to the right, bottom right and bottom, converts them back to YUV, averages the U and V values of those 4 pixels then converts the result back to RGB and returns it, effectively turning the ugly point resize that creates the blocky edges into a bilinear resize that is much easier on the eyes..."

Now I don't know if this can be done at the driver level ?

Do you think this can be solved relatively easily ? Also I tried the ATI open source driver "radeonhd" (on my desktop with a Radeon HD3850) and this issue was not present.

It seems like my is related to this one "xvideo: broken bilinear filter for the red color component": https://bugs.freedesktop.org/show_bug.cgi?id=19856

It should be fixed by the following commit:
commit 79b6851148574419389ac8055b0c31b8bdac3ab3
Author: Eric Anholt <eric@anholt.net>
Date:   Wed Aug 5 12:45:16 2009 -0700

    Fix sampler indexes on i965 planar video.

    We only set up one sampler, because all of our sampling is the same.  By
    using a non-zero index for the other two samplers, we'd dereference
(likely)
    zeroed data, resulting in using NEAREST filtering.  This was a regression
in
    40671132cb3732728703c6444f4577467fa9223f which incidentally switched from
    having 6 samplers to 1.

    Bug #22895, #19856


*** This bug has been marked as a duplicate of bug 22895 ***