Rolling on a rough incline - Part II

As the ball climbs up the inclined plane, its speed decreases due to gravity. For the pure rolling to occur, the relation $v=R\omega$ must hold. Therefore, with height angular speed must decrease as well. Only if the friction force acts up the inclined plane, it will decrease the angular speed.

For pure rolling, we know that $a=R \alpha$ . So $\alpha$ must be opposite to $a$ at the bottom most point and the $a$ is down the inclined plane so $\alpha$ must be clockwise. Since friction is the only force providing torque, so it must be up the inclined plane so as to provide clockwise $\alpha$ .

If the force of friction is not sufficient, i.e. the pure rolling does not happen, then also friction will be up the inclined plane so as to minimise the slipping.

(The error made by most of the people here is the wrong direction of $a$ . $a$ will be downwards only.)