Am 22.07.2014 06:05, schrieb Dave Airlie: > On 9 July 2014 22:29, Maarten Lankhorst <maarten.lankhorst at canonical.com> > wrote: >> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at canonical.com> >> --- >> drivers/gpu/drm/radeon/radeon.h | 15 +- >> drivers/gpu/drm/radeon/radeon_device.c | 60 ++++++++- >> drivers/gpu/drm/radeon/radeon_fence.c | 223 >> ++++++++++++++++++++++++++------ >> 3 files changed, 248 insertions(+), 50 deletions(-) >> > From what I can see this is still suffering from the problem that we > need to find a proper solution to, > > My summary of the issues after talking to Jerome and Ben and > re-reading things is: > > We really need to work out a better interface into the drivers to be > able to avoid random atomic entrypoints,
Which is exactly what I criticized from the very first beginning. Good to know that I'm not the only one thinking that this isn't such a good idea. > I'm sure you have some ideas and I think you really need to > investigate them to move this thing forward, > even it if means some issues with android sync pts. Actually I think that TTMs fence interface already gave quite a good hint how it might look like. I can only guess that this won't fit with the Android stuff, otherwise I can't see a good reason why we didn't stick with that. > but none of the two major drivers seem to want the interface as-is so > something needs to give > > My major question is why we need an atomic callback here at all, what > scenario does it cover? Agree totally. As far as I can see all current uses of the interface are of the kind of waiting for a fence to signal. No need for any callback from one driver into another, especially not in atomic context. If a driver needs such a functionality it should just start up a kernel thread and do it's waiting there. This obviously shouldn't be an obstacle for pure hardware implementations where one driver signals a semaphore another driver is waiting for, or a high signal on an interrupt line directly wired between two chips. And I think this is a completely different topic and not necessarily part of the common fence interface we should currently focus on. Christian. > Surely we can use a workqueue based callback to ask a driver to check > its signalling, is it really > that urgent? > > Dave.
