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@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