Hi Daniel, On Monday 25 January 2016 08:29:38 Daniel Vetter wrote: > On Mon, Jan 25, 2016 at 12:19:27AM +0200, Laurent Pinchart wrote: > > On Friday 15 January 2016 11:17:30 Daniel Vetter wrote: > >> On Fri, Jan 15, 2016 at 01:13:05AM +0200, Laurent Pinchart wrote: > >>> On Thursday 14 January 2016 16:24:56 Maxime Ripard wrote: > >>>> The drm_fbdev_cma_init function always calls the > >>>> drm_helper_disable_unused_functions. Since it's part of the usual > >>>> probe process, all the drivers using that helper will end up having > >>>> their encoder and CRTC disable functions called at probe if their > >>>> device has not been reported as enabled. > >>>> > >>>> This could be fixed by reading out from the registers the current > >>>> state of the device if it is enabled, but even that will not handle > >>>> the case where the device is actually disabled. > >>>> > >>>> Moreover, the drivers using the atomic modesetting expect that their > >>>> enable and disable callback to be called when the device is already > >>>> enabled or disabled (respectively). > >>>> > >>>> We can however fix this issue by moving the call to > >>>> drm_helper_disable_unused_functions out of drm_fbdev_cma_init and > >>>> make the drivers needing it (all the drivers calling > >>>> drm_fbdev_cma_init and not using the atomic modesetting) explicitly > >>>> call it. > >>> > >>> I'd rather add it to all drivers that call drm_fbdev_cma_init(). All > >>> the atomic ones must have special code to cope with it that could be > >>> rendered useless by the removal of the > >>> drm_helper_disable_unused_functions() call. That code should be > >>> removed too, and it would be easier to check drivers one by one and > >>> fixing them individually (outside of this patch series, unless you > >>> insist ;-)) when removing the explicit > >>> drm_helper_disable_unused_functions() call. > >> > >> I had the same thought, but figured there's really no good reason ever > >> to do this. I suspect most of that disable_unused_function stuff we have > >> all over is supreme cargo-cult anyway ;-) > > > > I'm not sure you got my point. Yes, the > > drm_helper_disable_unused_functions() call should be removed from atomic > > drivers, but that will leave support code added for the sole reason of > > avoiding the crash in the drivers. That code will likely not be noticed > > and will stay there rotting. If we added > > drm_helper_disable_unused_functions() calls to all atomic drivers then > > driver authors will hopefully check carefully if there's any support code > > that can be removed when removing the function call. It would act as a > > kind of FIXME reminder. > > drm_helper_disable_unused_functions() already prefers the ->disable > callbacks over dpms, like atomic helpers. I don't think there's any dead > code due to this change. The problem was that driver/hw blew up since it > was disabled when the hw was off already. The rcar-du-drm driver keeps an internal CRTC enabled state for just this purpose. I expect other drivers to implement something similar that can be removed after dropping the drm_helper_disable_unused_functions() calls. -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
