kernel at martin.sperl.org writes:

From: Martin Sperl <redacted>

The original patch contained 3 dma channels that were masked out.

These - as far as research and discussions show - are a
artefacts remaining from the downstream legacy dma-api.

Right now down-stream still includes a legacy api used only
in a single (downstream only) driver (bcm2708_fb) that requires
2D DMA for speedup (DMA-channel 0).
Formerly the sd-card support driver also was using this legacy
api (DMA-channel 2), but since has been moved over to use
dmaengine directly.

The DMA-channel 3 is already masked out in the devicetree in
the default property "brcm,dma-channel-mask = <0x7f35>;"

Delayed the rest of the review, because I went digging around in the
firmware, and missed the ifdef mess in it that produced 0x7f35.  As far
as I can tell, though, we should be using just that value to control
which channels we expose (other than the shared-irq issue).  If the
firmware wants to use a different set of channels some day, they'll have
to edit our DT.

Reviewed-by: Eric Anholt <redacted>
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