Linux driver support for ATI HD 6850

The AMD tool ATI Catalyst does not provide Linux support for the ATI HD 6850. Running the tool allows the monitor to display in 1080P. However, it results in a watermark stating the hardware isn’t supported.

Is there an open source driver that will support this card?

Can the Windows driver be co-opted for Linux?

When will there be an open source driver to support video cards?