linux-kernel - Re: [PATCH 3/3] Documentation: DT bindings: Tegra AHB: note base address change

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Date:	Thu, 19 Mar 2015 15:33:13 +0000 (UTC)
From:	Paul Walmsley <paul@...an.com>
To:	Stephen Warren <swarren@...dotorg.org>
cc:	linux-tegra@...r.kernel.org, linux-arm-kernel@...r.kernel.org,
	Mark Rutland <mark.rutland@....com>,
	Alexandre Courbot <gnurou@...il.com>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	linux-kernel@...r.kernel.org,
	Eduardo Valentin <edubezval@...il.com>,
	devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Kumar Gala <galak@...eaurora.org>,
	Hiroshi DOYU <hdoyu@...dia.com>
Subject: Re: [PATCH 3/3] Documentation: DT bindings: Tegra AHB: note base
 address change

On Tue, 17 Mar 2015, Stephen Warren wrote:

> On 03/17/2015 02:32 AM, Paul Walmsley wrote:
> > For Tegra132 and later chips, we can now use the correct hardware base
> > address for the Tegra AHB IP block in the DT data.  Update the DT binding
> > documentation to reflect this change.
> 
> > diff --git
> > a/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-ahb.txt
> > b/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-ahb.txt
> > index 067c979..7692b4c 100644
> > --- a/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-ahb.txt
> > +++ b/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-ahb.txt
> > @@ -2,10 +2,15 @@ NVIDIA Tegra AHB
> > 
> >   Required properties:
> >   - compatible : For Tegra20, must contain "nvidia,tegra20-ahb".  For
> > -  Tegra30, must contain "nvidia,tegra30-ahb".  Otherwise, must contain
> > -  '"nvidia,<chip>-ahb", "nvidia,tegra30-ahb"' where <chip> is tegra124,
> > -  tegra132, or tegra210.
> > -- reg : Should contain 1 register ranges(address and length)
> > +  Tegra30, must contain "nvidia,tegra30-ahb".  For Tegra114 and Tegra124,
> > must
> > +  contain '"nvidia,<chip>-ahb", "nvidia,tegra30-ahb"' where <chip> is
> > tegra114
> > +  or tegra124.  For Tegra132, the compatible string must contain
> > +  "nvidia,tegra132-ahb".
> > +
> > +- reg : Should contain 1 register ranges(address and length).  On Tegra20,
> > +  Tegra30, Tegra114, and Tegra124 chips, the low byte of the physical base
> > +  address of the IP block must end in 0x04.  On DT files for later chips,
> > the
> > +  actual hardware base address of the IP block should be used.
> 
> A table-based approach rather than prose might make this more legible?
> 
> - compatible: Must contain the following:
>   Tegra20:  "nvidia,tegra20-ahb"
>   Tegra30:  "nvidia,tegra30-ahb"
>   Tegra114: "nvidia,tegra114-ahb", "nvidia,tegra30-ahb"
>   Tegra124: "nvidia,tegra124-ahb", "nvidia,tegra30-ahb"
>   Tegra132: "nvidia,tegra132-ahb"
>   Tegra210: "nvidia,tegra210-ahb", "nvidia,tegra132-ahb"
> 
> With any luck, we can extend that final item for future chips to be:
> 
>   Tegra210, TegraNNN:
>             "nvidia,tegra<chip>-ahb", "nvidia,tegra132-ahb"
> 
> Perhaps we format the 114/124 entry that way too.

I think I'm just going to drop this patch, since Russell prefers that the 
workaround is applied in the driver.

With regards to using tables rather than narrative descriptions: perhaps 
consider a patch to 
Documentation/devicetree/bindings/submitting-patches.txt ?  I don't know 
what the DT binding documentation maintainers' future plans are with 
regards to automated documentation reflow, etc., but submitting a patch 
there would stimulate at least some coordination on the issue.

> As a historical note, I thought this issue might have been caused by the HW
> lumping together a bunch of vaguely related features into the same address
> window, with offset 0 being unrelated to AHB. This is certainly the
> explanation for some other interesting reg value in DT on other HW modules in
> Tegra. However as best I can tell that isn't the case for this HW module; we
> just mapped the start of the reg value to the first defined register for some
> reason rather than aligning it with the entry in the address map. So, this
> series makes sense to me.
> 
> The series,
> Acked-by: Stephen Warren <swarren@...dia.com>
> 
> (it'd be nice if the DT doc was modified as I described above, but not
> strictly necessary. I like Russell's ideas how to make this more
> transparent/automatic so old DTs can be converted too).

I'll add the ack on the first patch, but since the second one has been 
changed, I won't add one there yet.


- Paul
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