Am Dienstag, den 22.01.2013, 18:37 +0100 schrieb Mario Kleiner:
> On 14.01.13 17:05, Thierry Reding wrote:
> > Implement support for the VBLANK IOCTL. Note that Tegra is somewhat
> > special in this case because it doesn't use the generic IRQ support
> > provided by the DRM core (DRIVER_HAVE_IRQ) but rather registers one
> > interrupt handler for each display controller.
> >
> > While at it, clean up the way that interrupts are enabled to ensure
> > that the VBLANK interrupt only gets enabled when required.
> >
> > Signed-off-by: Thierry Reding <thierry.reding at avionic-design.de>
>
> ... snip ...
>
> > struct drm_driver tegra_drm_driver = {
> > .driver_features = DRIVER_BUS_PLATFORM | DRIVER_MODESET | DRIVER_GEM,
> > .load = tegra_drm_load,
> > @@ -96,6 +136,10 @@ struct drm_driver tegra_drm_driver = {
> > .open = tegra_drm_open,
> > .lastclose = tegra_drm_lastclose,
> >
> > + .get_vblank_counter = drm_vblank_count,
>
> -> .get_vblank_counter = drm_vblank_count is a no-op.
>
> .get_vblank_counter() is supposed to return some real hardware vblank
> counter value to reinitialize the software vblank counter at vbl irq
> enable time. That software counter gets queried via drm_vblank_count().
> If you hook this up to drm_vblank_count() it essentially returns a
> constant, frozen vblank count, it has the same effect as returning zero
> or any other constant value -- You lose all vblank counter increments
> during vblank irq off time. The same problem is present in nouveau-kms.
>
> I think it would be better to either implement a real hw counter query,
> or some function with a /* TODO: Implement me properly */ comment which
> returns zero, so it is clear something is missing here.
>
I've looked this up in the TRM a while ago as I know we have the same
problem in nouveau, but it seems there is no HW vblank counter on Tegra.
Mario, you know a fair bit more about this than I do, what is the
preferred way of handling this if we are sure we are not able to
implement anything meaningful here? Just return 0?
Regards,
Lucas
