RADEON_SPLL_FB_DIV_MASK
tmp &= ~(RADEON_SPLL_FB_DIV_MASK << RADEON_SPLL_FB_DIV_SHIFT);
tmp |= (fb_div & RADEON_SPLL_FB_DIV_MASK) << RADEON_SPLL_FB_DIV_SHIFT;
fb_div = (fb_div >> RADEON_SPLL_FB_DIV_SHIFT) & RADEON_SPLL_FB_DIV_MASK;