[PATCH xserver 3/6] modesetting: add DRI2 page flip support

[Yu, Qiang]

> +static Bool
> +can_exchange(ScrnInfoPtr scrn, DrawablePtr draw,
> +          DRI2BufferPtr front, DRI2BufferPtr back)
> +{

[...]

> +    if (!update_front(draw, front))
> +        return FALSE;

I know you just copied this from -ati/amdgpu, but: I don't think
can_exchange should call update_front, or the front buffer may be
updated even though the flip later fails.
[yuq] so you mean I can just drop update_front here and use "front"
directly?


> +    /* Post damage on the front buffer so that listeners, such
> +     * as DisplayLink know take a copy and shove it over the USB.
> +     * also for sw cursors.
> +     */

SW cursors cannot work correctly with page flipping. For that reason,
xf86-video-ati/amdgpu disable page flipping while there's an SW cursor.
[yuq] why? Is the problem in kernel or xserver?

Regards,
Qiang