linux-kernel - Re: [PATCH 2/8 v2] Documentation: bindings: k3dma: Add binding for dma-avail-chan

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Date:   Fri, 4 Jan 2019 20:58:03 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     lkml <linux-kernel@...r.kernel.org>, Vinod Koul <vkoul@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Tanglei Han <hantanglei@...wei.com>,
        Zhuangluan Su <suzhuangluan@...ilicon.com>,
        Ryan Grachek <ryan@...ted.us>, dmaengine@...r.kernel.org,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH 2/8 v2] Documentation: bindings: k3dma: Add binding for dma-avail-chan

On Fri, Jan 4, 2019 at 8:53 PM Manivannan Sadhasivam
<manivannan.sadhasivam@...aro.org> wrote:
>
> On Fri, Jan 04, 2019 at 08:39:34PM -0800, John Stultz wrote:
> > On Fri, Jan 4, 2019 at 8:00 PM Manivannan Sadhasivam
> > <manivannan.sadhasivam@...aro.org> wrote:
> > >
> > > Hi John,
> > >
> > > On Fri, Jan 04, 2019 at 12:56:22PM -0800, John Stultz wrote:
> > > > Some dma channels can be reserved for secure mode or other
> > > > hardware on the SoC, so provide a binding for a bitmask
> > > > listing the available channels for the kernel to use.
> > > >
> > > > Cc: Vinod Koul <vkoul@...nel.org>
> > > > Cc: Rob Herring <robh+dt@...nel.org>
> > > > Cc: Mark Rutland <mark.rutland@....com>
> > > > Cc: Tanglei Han <hantanglei@...wei.com>
> > > > Cc: Zhuangluan Su <suzhuangluan@...ilicon.com>
> > > > Cc: Ryan Grachek <ryan@...ted.us>
> > > > Cc: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > > > Cc: dmaengine@...r.kernel.org
> > > > Cc: devicetree@...r.kernel.org
> > > > Signed-off-by: John Stultz <john.stultz@...aro.org>
> > > > ---
> > > >  Documentation/devicetree/bindings/dma/k3dma.txt | 3 +++
> > > >  1 file changed, 3 insertions(+)
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/dma/k3dma.txt b/Documentation/devicetree/bindings/dma/k3dma.txt
> > > > index 10a2f15..1c466c1 100644
> > > > --- a/Documentation/devicetree/bindings/dma/k3dma.txt
> > > > +++ b/Documentation/devicetree/bindings/dma/k3dma.txt
> > > > @@ -14,6 +14,9 @@ Required properties:
> > > >               have specific request line
> > > >  - clocks: clock required
> > > >
> > > > +Optional properties:
> > > > +- dma-avail-chan: Bitmask of available physical channels
> > > > +
> > >
> > > This property looks too generic. Since this is specific to HiSi SoCs,
> > > this could be "hisi-dma-avail-chan"?
> >
> > I'm fine to change it, but I'm not sure I fully understand the
> > rational. Can you help me understand?
> > Are device node-binding names supposed to have global scope? I assumed
> > the node property names are basically scoped to the entry?
>
> IIUC properties documented in subsystem binding (dma.txt in this case)
> will have global scope. Those which are not documented in this binding
> are specific to vendor IPs and should be prefixed with the vendor
> prefix (hisi in this case).

Thanks I appreciate the explanation here. I hadn't really understood
this point, and really haven't developed much "taste" in what makes a
good or bad binding.

> > Further, having some dma channels be reserved doesn't seem to be too
> > unique a concept, so I'm not sure what we gain long term by prefixing
> > it?
> >
>
> Right, but this brings up the point of having this functionality in
> generic DMA engine so that the DMA controller drivers need not handle.
> So either we should move this available channel check to DMA Engine
> and document the property in dma.txt so that other IPs can also use it
> or keep the functionality in K3 driver and use HiSi prefix for the
> property.
>
> But I'd like to hear Vinod/Rob's opinion on this!

Sure. Though for now I'll prefix it as the logic is handled at the
driver level.

thanks
-john