On Fri, Jul 10, 2020 at 04:02:35PM +0200, Daniel Vetter wrote:

quoted

dma_fence only possibly makes some sense if you intend to expose the
completion outside a single driver.

The prefered kernel design pattern for this is to connect things with
a function callback.

So the actual use case of dma_fence is quite narrow and tightly linked
to DRM.

I don't think we should spread this beyond DRM, I can't see a reason.

Yeah v4l has a legit reason to use dma_fence, android wants that
there. 

'legit' in the sense the v4l is supposed to trigger stuff in DRM when
V4L DMA completes? I would still see that as part of DRM

Or is it building a parallel DRM like DMA completion graph?

quoted

Trying to improve performance of limited HW by using sketchy
techniques at the cost of general system stability should be a NAK.

Well that's pretty much gpu drivers, all the horrors for a bit more speed :-)

On the text itself, should I upgrade to "must not" instead of "should
not"? Or more needed?

Fundamentally having some unknowable graph of dependencies where parts
of the graph can be placed in critical regions like notifiers is a
complete maintenance nightmare.

I think building systems like this should be discouraged :\

Jason