lkml.org 
[lkml]   [2022]   [Jun]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RESEND PATCH v3] drm/cma-helper: Describe what a "contiguous chunk" actually means
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@linaro.org>
> > Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
> > ---
> >
> > 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.

\
 
 \ /
  Last update: 2022-06-09 11:20    [W:0.038 / U:0.944 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site