Hello again, and thanks for your response.
I checked the link you provided. Out of curiosity I downloaded the x.org driver sources and find this release the NEWS.
Release 2.20.5 (2012-08-26)
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Another silly bug found, another small bugfix release. The goal was for
the driver to bind to all Intel devices supported by the kernel.
Unfortunately we were too successful and started claiming Pouslbo,
Medfield and Cedarview devices which are still encumbered by propietary
IP and not supported by this driver.
The release states that Medfield and Cedarview devices are not supported because they are encumbered by proprietary IP. In other words, in this case the developers of the open-source Linux drivers are prevented from providing a driver for these graphics chipsets.
Is there any hope that this situation will change?