[RFC v4 00/18] vb2: Handle user cache hints, allow drivers to choose cache coherency

[Mauro Carvalho Chehab]

Hi Sakari,

Em Mon,  8 May 2017 18:03:12 +0300
Sakari Ailus <sakari.ailus at linux.intel.com> escreveu:

> Hello,
> 
> This is a rebased and partially reworked version of the vb2 cache hints
> support patch series posted by first myself, then Laurent and then myself
> again.
> 
> I'm still posting this as RFC primarily because more testing and driver
> changes will be needed. In particular, a lot of platform drivers assume
> non-coherent memory but are not properly labelled as such.

The main issue I see is that, if the driver doesn't "annotate" if it
is requiring coherent or non-coherent memory, VB2 should be preserving
its old behavior, as, otherwise, it will risk causing regressions. 

So, perhaps instead of creating a single flag
V4L2_BUF_FLAG_NO_CACHE_SYNC, it would make sense to create two
flags, using either one of them on newer drivers. For old drivers
that won't set either, it would keep the current behavior.

Thanks,
Mauro