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

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Date:	Thu, 19 Mar 2015 16:34:42 +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 Thu, 19 Mar 2015, Stephen Warren wrote:

> On 03/19/2015 09:33 AM, Paul Walmsley wrote:
> > 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.
> 
> I don't think it's appropriate for that file to dictate that, in the same way
> that coding style documentation generally doesn't address that kind of detail
> regarding code structure.

We do indeed specify details like this in our documentation guidelines.  
Here are two examples:

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/kernel-doc-nano-HOWTO.txt#n103

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/CodingStyle#n464

> Rather, the code review process hopefully homes in on the best 
> representation case-by-case. A table seems more succinct and unambiguous 
> in this case. 

I understand that your point of view in this case is that the table format 
is superior.  My point of view on this issue, which is that any potential 
improvement in using a table format is outweighed by the time involved in 
doing it.  Additionally I believe that the presence of the information is 
the most important criterion.  

My point of view is also that formatting guidelines should be coordinated 
at a kernel-wide level with the DT maintainers and placed into common 
policy documentation.  That way everyone's expectations are aligned.  
Reviews can be based on shared rules, rather than individual whim.  Such 
an approach also codifies expectations for programs that operate on 
documentation data, like the scripts/kernel-doc code.


- Paul
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