[PATCH 0/7] sunxi: Add DT representation for the MBUS controller

Maxime Ripard maxime.ripard at bootlin.com
Thu May 31 12:52:27 UTC 2018

On Mon, Apr 09, 2018 at 11:22:29AM +0200, Maxime Ripard wrote:
> Hi Rob,
> On Tue, Apr 03, 2018 at 11:03:30AM -0500, Rob Herring wrote:
> > On Tue, Apr 3, 2018 at 8:29 AM, Maxime Ripard <maxime.ripard at bootlin.com> wrote:
> > > Hi,
> > >
> > > We've had for quite some time to hack around in our drivers to take into
> > > account the fact that our DMA accesses are not done through the parent
> > > node, but through another bus with a different mapping than the CPU for the
> > > RAM (0 instead of 0x40000000 for most SoCs).
> > >
> > > After some discussion after the submission of a camera device suffering of
> > > the same hacks, I've decided to put together a serie that introduce a
> > > property called dma-parent that allows to express the DMA relationship
> > > between a master and its bus, even if they are not direct parents in the DT.
> > 
> > Reading thru v6 of the camera driver, it seems like having
> > intermediate buses would solve the problem in your case?
> I guess it would yes, but I guess it wouldn't model the hardware
> properly since this seems to be really a bus only meant to do DMA, and
> you're not accessing the registers of the device through that bus.
> And as far as I know, the DT implies that the topology is the one of
> the "control" side of the devices.
> We'll also need eventually to have retrieve the MBUS endpoints ID to
> be able to support perf and PM QoS properly.
> > As Arnd mentioned in that thread, something new needs to address all
> > the deficiencies with dma-ranges and describing DMA bus topologies.
> > This doesn't address the needs of describing bus interconnects.
> > There's been some efforts by the QCom folks with an interconnect
> > binding. They've mostly punted (for now at least) to not describing
> > the whole interconnect in DT and keeping the details in a driver.
> Is it that patch serie? https://lkml.org/lkml/2018/3/9/856
> > On the flip side, this does mirror the established pattern used by
> > interrupts, so maybe it's okay on it's own. I'll wait for others to
> > comment.
> We'll see how it turns out then :)


How should we move forward on this?


Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
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