Re: [PATCH v8 1/4] dt-bindings: dmaengine: Add MediaTek Command-Queue DMA controller bindings

Vinod Koul
2021-01-12T12:14:02Z

On 06-01-21, 16:53, Rob Herring wrote:

> > > > + dma-channel-mask:
> > > > + description:
> > > > + For DMA capability, We will know the addressing capability of
> > > > + MediaTek Command-Queue DMA controller through dma-channel-mask.
> > > > + minimum: 1
> > > > + maximum: 63
> > >
> > > Indentation is wrong here so this has no effect.
> > I'll fix it
> > >
> > > A mask of 63 is 6 channels...
> > In my opinion, kernel dma mask if for 32/64 bit capability...
> > If I don't set dma mask I will get fail on DMATEST.
>
> As in the kernel's 'dma_mask'? That's something entirely different.
> The driver should set the mask to the max the device supports.
> Typically this is a 32-bit or 64-bit mask. The default is 32-bit. If
> the SoC has limitations in its buses, then you need to use
> 'dma-ranges' in DT which will in turn set the bus_dma_limit.

Correct, dma_mask tells dmatest the capability of the device and should
be set accordingly

dma-channel-mask defines the 'Bitmask of available DMA channels' and is
deined in dma-common.yaml

--
~Vinod