On Wed, Jun 08, 2022 at 05:37:50PM +0200, Daniel Vetter wrote: > On Wed, Jun 08, 2022 at 02:58:21PM +0100, Daniel Thompson wrote: > > Since it's inception in 2012 it has been understood that the DRM GEM CMA > > helpers do not depend on CMA as the backend allocator. In fact the first > > bug fix to ensure the cma-helpers work correctly with an IOMMU backend > > appeared in 2014. However currently the documentation for > > drm_gem_cma_create() talks about "a contiguous chunk of memory" without > > making clear which address space it will be a contiguous part of. > > Additionally the CMA introduction is actively misleading because it only > > contemplates the CMA backend. > > > > This matters because when the device accesses the bus through an IOMMU > > (and don't use the CMA backend) then the allocated memory is contiguous > > only in the IOVA space. This is a significant difference compared to the > > CMA backend and the behaviour can be a surprise even to someone who does > > a reasonable level of code browsing (but doesn't find all the relevant > > function pointers ;-) ). > > > > Improve the kernel doc comments accordingly. > > > > Signed-off-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx> > > Reviewed-by: Lucas Stach <l.stach@xxxxxxxxxxxxxx> > > --- > > > > Notes: > > Am I Cc:ing the correct reviewers/maintainers with this patch? There > > has been no negative feedback but I've been rebasing and re-posting it > > for three kernel cycles now. Do I need to queue it somewhere special or > > get it in front of someone specific? > > Occasionally stuff falls through a few too many cracks, that's all. We > have tons of committers for drm-misc (and Lucas is one of them), but > sometimes they shy away from pushing themselves and others see the r-b and > assume it's already handled, and then it doesn't move :-/ No worries. Arguably I should have asked this question a little earlier anyway. Thanks for pushing it. Daniel.
