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

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Date:   Tue, 12 Jan 2021 17:43:33 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Rob Herring <robh@...nel.org>
Cc:     EastL <EastL.Lee@...iatek.com>, Sean Wang <sean.wang@...iatek.com>,
        Mark Rutland <mark.rutland@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "open list:DMA GENERIC OFFLOAD ENGINE SUBSYSTEM" 
        <dmaengine@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>, devicetree@...r.kernel.org,
        wsd_upstream <wsd_upstream@...iatek.com>,
        CC Hwang <cc.hwang@...iatek.com>
Subject: Re: [PATCH v8 1/4] dt-bindings: dmaengine: Add MediaTek
 Command-Queue DMA controller bindings

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