linux-kernel - Re: [PATCH v2 7/9] ARM: STi: DT: STiH407: Add FDMA driver dt nodes.

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Date:	Sat, 12 Sep 2015 13:23:22 +0100
From:	Peter Griffin <peter.griffin@...aro.org>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	srinivas.kandagatla@...il.com, maxime.coquelin@...com,
	patrice.chotard@...com, vinod.koul@...el.com, robh+dt@...nel.org,
	dmaengine@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v2 7/9] ARM: STi: DT: STiH407: Add FDMA driver dt nodes.

Hi Lee,

On Fri, 11 Sep 2015, Lee Jones wrote:

> On Fri, 11 Sep 2015, Peter Griffin wrote:
> > On Fri, 11 Sep 2015, Lee Jones wrote:
> > > On Fri, 11 Sep 2015, Peter Griffin wrote:
> > > > On Fri, 11 Sep 2015, Lee Jones wrote:
> > > > > On Fri, 11 Sep 2015, Peter Griffin wrote:
> > > > > 
> > > > > > These nodes are required to get the fdma driver working
> > > > > > on STiH407 based silicon.
> > > > > > 
> > > > > > Signed-off-by: Peter Griffin <peter.griffin@...aro.org>
> > > > > > ---
> > > > > >  arch/arm/boot/dts/stih407-family.dtsi | 51 +++++++++++++++++++++++++++++++++++
> > > > > >  1 file changed, 51 insertions(+)
> > > > > > 
> > > > > > diff --git a/arch/arm/boot/dts/stih407-family.dtsi b/arch/arm/boot/dts/stih407-family.dtsi
> > > > > > index 838b812..da07474b 100644
> > > > > > --- a/arch/arm/boot/dts/stih407-family.dtsi
> > > > > > +++ b/arch/arm/boot/dts/stih407-family.dtsi
> > > > > > @@ -565,5 +565,56 @@
> > > > > >  						  <&phy_port2 PHY_TYPE_USB3>;
> > > > > >  			};
> > > > > >  		};
> > > > > > +
> > > > > > +		fdma0: fdma0-audio@...0000 {
> > > > > 
> > > > > I'm not familiar with the FDMA driver, so can't comment knowledgeably,
> > > > > but the <dev> part of <dev>@<base_address> should only describe the
> > > > > type of hardware.  I believe in this case it should just be
> > > > > dma@...20000.  Also notice the leading zero in the address, which I
> > > > > believe mitigates possible confusion.  Then you be more specific with
> > > > > the label, so something like 'fdma-audio' seems appropriate here.
> > > > 
> > > > Ok, can change to that format in v3.
> > > > 
> > > > > 
> > > > > > +			compatible = "st,stih407-fdma-mpe31";
> > > > > > +			reg = <0x8e20000 0x20000>;
> > > > > 
> > > > > I personally find padding up to 32bits helpful in the addresses.
> > > > 
> > > > None of the stih407-family nodes I can see have this padding, including
> > > > the ones merged by you.
> > > 
> > > Nither of these two facts mean it's correct.
> > 
> > I thought it was a 'personal' thing. If it is mandated by the spec, then that
> > is different.
> > 
> > > 
> > > I'm happy to write a patch to correct them all.
> > 
> > Are you sure your actually correcting anything? Where does it say you
> > should have a leading zero?
> > 
> > > 
> > > Bear in mind that this isn't a hard and fast rule.  Both work and are
> > > legal.  I just think the padding is more consistent.
> > 
> > Surely adding a patch with how the nodes are currently formatted, is more consistent
> > than adding a patch with padding?
>  
> I did mean consistent with the majority of DTS files, rather than just
> ours.  There are examples of non-padded values and it's perfectly
> legal, but the vast majority of examples do in fact pad their
> addresses [see below].  The change is more of a nit than a blocker.

If its perdectly legal, than I'm personally against changing it.
Mainly because it makes it difficult for git and patch to apply
patches from the vendor kernel on top of the upstream kernel
without manual intervention.

I already ran into this with the recent stih407-pinctrl series
where every patch had to be manually fixed up because we changed
PIO to pio, on every pin definition.

I'm all for changing things where they are actually wrong in the
vendor kernel (such as not having the unit address on the reg property,
or the node name being wrong e.g. fdma to dma-controller etc. But this
doesn't appar to be one of those cases.

regards,

Peter.
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