Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1593322

Re: [RFC PATCH 10/12] staging: android: ion: Use CMA APIs directly

From Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Newsgroups linux.kernel
Subject Re: [RFC PATCH 10/12] staging: android: ion: Use CMA APIs directly
Date 2017-03-06 14:50 +0100
Message-ID <ti1br-uP-5@gated-at.bofh.it> (permalink)
References <tgGLL-8cb-5@gated-at.bofh.it> <th0AN-5fC-7@gated-at.bofh.it> <thYng-6U9-25@gated-at.bofh.it>
Organization linux.* mail to news gateway

Show all headers | View raw

Hi Daniel,

On Monday 06 Mar 2017 11:32:04 Daniel Vetter wrote:
> On Fri, Mar 03, 2017 at 10:50:20AM -0800, Laura Abbott wrote:
> > On 03/03/2017 08:41 AM, Laurent Pinchart wrote:
> >> On Thursday 02 Mar 2017 13:44:42 Laura Abbott wrote:
> >>> When CMA was first introduced, its primary use was for DMA allocation
> >>> and the only way to get CMA memory was to call dma_alloc_coherent. This
> >>> put Ion in an awkward position since there was no device structure
> >>> readily available and setting one up messed up the coherency model.
> >>> These days, CMA can be allocated directly from the APIs. Switch to
> >>> using this model to avoid needing a dummy device. This also avoids
> >>> awkward caching questions.
> >> 
> >> If the DMA mapping API isn't suitable for today's requirements anymore,
> >> I believe that's what needs to be fixed, instead of working around the
> >> problem by introducing another use-case-specific API.
> > 
> > I don't think this is a usecase specific API. CMA has been decoupled from
> > DMA already because it's used in other places. The trying to go through
> > DMA was just another layer of abstraction, especially since there isn't
> > a device available for allocation.
> 
> Also, we've had separation of allocation and dma-mapping since forever,
> that's how it works almost everywhere. Not exactly sure why/how arm-soc
> ecosystem ended up focused so much on dma_alloc_coherent.

I believe because that was the easy way to specify memory constraints. The API 
receives a device pointer and will allocate memory suitable for DMA for that 
device. The fact that it maps it to the device is a side-effect in my opinion.

> I think separating allocation from dma mapping/coherency is perfectly
> fine, and the way to go.

Especially given that in many cases we'll want to share buffers between 
multiple devices, so we'll need to map them multiple times.

My point still stands though, if we want to move towards a model where 
allocation and mapping are decoupled, we need an allocation function that 
takes constraints (possibly implemented with two layers, a constraint 
resolution layer on top of a pool/heap/type/foo-based allocator), and a 
mapping API. IOMMU handling being integrated in the DMA mapping API we're 
currently stuck with it, which might call for brushing up that API.

-- 
Regards,

Laurent Pinchart

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[RFC PATCH 00/12] Ion cleanup in preparation for moving out of staging Laura Abbott <labbott@redhat.com> - 2017-03-02 22:50 +0100
  [RFC PATCH 01/12] staging: android: ion: Remove dmap_cnt Laura Abbott <labbott@redhat.com> - 2017-03-02 22:50 +0100
  [RFC PATCH 10/12] staging: android: ion: Use CMA APIs directly Laura Abbott <labbott@redhat.com> - 2017-03-02 22:50 +0100
    Re: [RFC PATCH 10/12] staging: android: ion: Use CMA APIs directly Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2017-03-03 17:50 +0100
      Re: [RFC PATCH 10/12] staging: android: ion: Use CMA APIs directly Laura Abbott <labbott@redhat.com> - 2017-03-03 20:00 +0100
        Re: [RFC PATCH 10/12] staging: android: ion: Use CMA APIs directly Daniel Vetter <daniel@ffwll.ch> - 2017-03-06 11:50 +0100
          Re: [RFC PATCH 10/12] staging: android: ion: Use CMA APIs directly Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2017-03-06 14:50 +0100
            Re: [RFC PATCH 10/12] staging: android: ion: Use CMA APIs directly Daniel Vetter <daniel@ffwll.ch> - 2017-03-06 17:00 +0100
              Re: [RFC PATCH 10/12] staging: android: ion: Use CMA APIs directly Laura Abbott <labbott@redhat.com> - 2017-03-06 20:30 +0100
  [RFC PATCH 09/12] cma: Introduce cma_for_each_area Laura Abbott <labbott@redhat.com> - 2017-03-02 22:50 +0100
  [RFC PATCH 03/12] staging: android: ion: Duplicate sg_table Laura Abbott <labbott@redhat.com> - 2017-03-02 22:50 +0100
    Re: [RFC PATCH 03/12] staging: android: ion: Duplicate sg_table "Hillf Danton" <hillf.zj@alibaba-inc.com> - 2017-03-03 09:40 +0100
      Re: [RFC PATCH 03/12] staging: android: ion: Duplicate sg_table Laura Abbott <labbott@redhat.com> - 2017-03-03 19:50 +0100
  [RFC PATCH 11/12] staging: android: ion: Make Ion heaps selectable Laura Abbott <labbott@redhat.com> - 2017-03-02 22:50 +0100
    Re: [RFC PATCH 11/12] staging: android: ion: Make Ion heaps  selectable Daniel Vetter <daniel@ffwll.ch> - 2017-03-03 16:10 +0100
      Re: [RFC PATCH 11/12] staging: android: ion: Make Ion heaps  selectable Laura Abbott <labbott@redhat.com> - 2017-03-03 20:50 +0100
  [RFC PATCH 05/12] staging: android: ion: Remove page faulting support Laura Abbott <labbott@redhat.com> - 2017-03-02 22:50 +0100
  [RFC PATCH 02/12] staging: android: ion: Remove alignment from allocation field Laura Abbott <labbott@redhat.com> - 2017-03-02 22:50 +0100
  [RFC PATCH 04/12] staging: android: ion: Call dma_map_sg for syncing and mapping Laura Abbott <labbott@redhat.com> - 2017-03-02 22:50 +0100
    Re: [RFC PATCH 04/12] staging: android: ion: Call dma_map_sg for  syncing and mapping Dan Carpenter <dan.carpenter@oracle.com> - 2017-03-03 12:10 +0100
      Re: [RFC PATCH 04/12] staging: android: ion: Call dma_map_sg for  syncing and mapping Eric Engestrom <eric.engestrom@imgtec.com> - 2017-03-03 13:00 +0100
    Re: [RFC PATCH 04/12] staging: android: ion: Call dma_map_sg for syncing and mapping Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2017-03-03 17:40 +0100
      Re: [RFC PATCH 04/12] staging: android: ion: Call dma_map_sg for  syncing and mapping Laura Abbott <labbott@redhat.com> - 2017-03-03 19:50 +0100
  [RFC PATCH 07/12] staging: android: ion: Remove old platform support Laura Abbott <labbott@redhat.com> - 2017-03-02 22:50 +0100
    Re: [RFC PATCH 07/12] staging: android: ion: Remove old platform  support Daniel Vetter <daniel@ffwll.ch> - 2017-03-03 11:40 +0100
  [RFC PATCH 06/12] staging: android: ion: Remove crufty cache support Laura Abbott <labbott@redhat.com> - 2017-03-02 22:50 +0100
    Re: [RFC PATCH 06/12] staging: android: ion: Remove crufty cache  support Daniel Vetter <daniel@ffwll.ch> - 2017-03-03 11:00 +0100
      Re: [RFC PATCH 06/12] staging: android: ion: Remove crufty cache support Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2017-03-03 18:00 +0100
        Re: [RFC PATCH 06/12] staging: android: ion: Remove crufty cache  support Laura Abbott <labbott@redhat.com> - 2017-03-03 19:50 +0100
          Re: [RFC PATCH 06/12] staging: android: ion: Remove crufty cache  support Daniel Vetter <daniel@ffwll.ch> - 2017-03-06 11:50 +0100
            Re: [RFC PATCH 06/12] staging: android: ion: Remove crufty cache support Emil Velikov <emil.l.velikov@gmail.com> - 2017-03-06 18:40 +0100
              Re: [RFC PATCH 06/12] staging: android: ion: Remove crufty cache  support Laura Abbott <labbott@redhat.com> - 2017-03-06 20:30 +0100
  Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Daniel Vetter <daniel@ffwll.ch> - 2017-03-03 11:40 +0100
    Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Daniel Vetter <daniel@ffwll.ch> - 2017-03-03 11:40 +0100
      Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of staging Benjamin Gaignard <benjamin.gaignard@linaro.org> - 2017-03-03 15:50 +0100
    Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of staging Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2017-03-03 17:50 +0100
      Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Laura Abbott <labbott@redhat.com> - 2017-03-03 20:20 +0100
      Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Daniel Vetter <daniel@ffwll.ch> - 2017-03-06 11:50 +0100
        Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of staging Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2017-03-06 16:10 +0100
          Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Daniel Vetter <daniel@ffwll.ch> - 2017-03-06 17:40 +0100
  Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Michal Hocko <mhocko@kernel.org> - 2017-03-03 14:40 +0100
    Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Laura Abbott <labbott@redhat.com> - 2017-03-03 18:50 +0100
      Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Michal Hocko <mhocko@kernel.org> - 2017-03-06 09:10 +0100
        Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Daniel Vetter <daniel@ffwll.ch> - 2017-03-06 12:00 +0100
          Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Mark Brown <broonie@kernel.org> - 2017-03-06 12:00 +0100
            Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Daniel Vetter <daniel@ffwll.ch> - 2017-03-06 17:20 +0100
              Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of staging Benjamin Gaignard <benjamin.gaignard@linaro.org> - 2017-03-09 11:10 +0100
                Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Laura Abbott <labbott@redhat.com> - 2017-03-09 19:10 +0100
                Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Brian Starkey <brian.starkey@arm.com> - 2017-03-10 11:40 +0100
                Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Robin Murphy <robin.murphy@arm.com> - 2017-03-10 12:50 +0100
                Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Brian Starkey <brian.starkey@arm.com> - 2017-03-10 15:30 +0100
                Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Laura Abbott <labbott@redhat.com> - 2017-03-10 17:50 +0100
                Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Daniel Vetter <daniel@ffwll.ch> - 2017-03-10 13:50 +0100
                Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of staging Rob Clark <robdclark@gmail.com> - 2017-03-10 15:00 +0100
                Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of staging Benjamin Gaignard <benjamin.gaignard@linaro.org> - 2017-03-12 14:40 +0100
                Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of staging Daniel Vetter <daniel.vetter@ffwll.ch> - 2017-03-12 20:10 +0100
                Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Laura Abbott <labbott@redhat.com> - 2017-03-13 22:20 +0100
                Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of staging Rob Clark <robdclark@gmail.com> - 2017-03-13 22:30 +0100
                Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Laura Abbott <labbott@redhat.com> - 2017-03-13 23:00 +0100
                Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Brian Starkey <brian.starkey@arm.com> - 2017-03-13 12:00 +0100
                Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Mark Brown <broonie@kernel.org> - 2017-03-13 14:30 +0100
                Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Laura Abbott <labbott@redhat.com> - 2017-03-13 22:50 +0100
                Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Laura Abbott <labbott@redhat.com> - 2017-03-13 22:30 +0100
          Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Michal Hocko <mhocko@kernel.org> - 2017-03-06 14:40 +0100
  Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of staging Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2017-03-03 17:30 +0100
    Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of  staging Laura Abbott <labbott@redhat.com> - 2017-03-03 20:20 +0100

csiph-web