linux-kernel - Re: [PATCH v3 4/4] soc: Add SoC driver for Freescale Vybrid platform

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Date:	Tue, 24 May 2016 09:44:47 +0530
From:	maitysanchayan@...il.com
To:	Rob Herring <robh@...nel.org>
Cc:	arnd@...db.de, shawnguo@...nel.org, stefan@...er.ch,
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/4] soc: Add SoC driver for Freescale Vybrid platform

Hello Rob,

On 16-05-23 16:18:13, Rob Herring wrote:
> On Fri, May 20, 2016 at 03:32:05PM +0530, Sanchayan Maity wrote:
> > This adds a SoC driver to be used by Freescale Vybrid SoC's.
> > Driver utilises syscon and nvmem consumer API's to get the
> > various register values needed and expose the SoC specific
> > properties via sysfs.
> > 
> > A sample output from Colibri Vybrid VF61 is below:
> > 
> > root@...ibri-vf:~# cd /sys/bus/soc/devices/soc0
> > root@...ibri-vf:/sys/bus/soc/devices/soc0# ls
> > family     machine    power      revision   soc_id     subsystem  uevent
> > root@...ibri-vf:/sys/bus/soc/devices/soc0# cat family
> > Freescale Vybrid VF610
> > root@...ibri-vf:/sys/bus/soc/devices/soc0# cat machine
> > Freescale Vybrid
> > root@...ibri-vf:/sys/bus/soc/devices/soc0# cat revision
> > 00000013
> > root@...ibri-vf:/sys/bus/soc/devices/soc0# cat soc_id
> > df6472a6130f29d4
> > 
> > Signed-off-by: Sanchayan Maity <maitysanchayan@...il.com>
> > ---
> >  .../bindings/arm/freescale/fsl,vf610-soc.txt       |  20 +++
> >  drivers/soc/Kconfig                                |   1 +
> >  drivers/soc/fsl/Kconfig                            |  10 ++
> >  drivers/soc/fsl/Makefile                           |   1 +
> >  drivers/soc/fsl/soc-vf610.c                        | 198 +++++++++++++++++++++
> >  5 files changed, 230 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/arm/freescale/fsl,vf610-soc.txt
> >  create mode 100644 drivers/soc/fsl/Kconfig
> >  create mode 100644 drivers/soc/fsl/soc-vf610.c
> > 
> > diff --git a/Documentation/devicetree/bindings/arm/freescale/fsl,vf610-soc.txt b/Documentation/devicetree/bindings/arm/freescale/fsl,vf610-soc.txt
> > new file mode 100644
> > index 0000000..338905d
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/arm/freescale/fsl,vf610-soc.txt
> > @@ -0,0 +1,20 @@
> > +Vybrid System-on-Chip
> > +---------------------
> > +
> > +Required properties:
> > +
> > +- compatible: "fsl,vf610-soc"
> > +- rom-revision: phandle to the on-chip ROM node
> > +- mscm: phandle to the MSCM CPU configuration node
> > +- nvmem-cells: phandles to two OCOTP child nodes ocotp_cfg0 and ocotp_cfg1
> > +- nvmem-cell-names: should contain string names "cfg0" and "cfg1"
> 
> I still have similar concerns as the discussion on the last version. 
> This version only proves that you aren't describing h/w, but rather just 
> a collection of data that some driver wants.
> 
> A driver can just as easily look-up all the nodes directly that these 
> phandles point to.

Agreed, that we can look up all the nodes directly that these phandles
refer to but I would still need a DT entry to bind to. While I could
bind to existing nodes like mscm cpucfg but that doesn't seem right.

The very first approach that we had taken was to integrate this functionality
in mach-vf610.c code under mach-imx
http://www.spinics.net/lists/devicetree/msg80654.html

and then it was recommended to migrate this to drivers/soc where we did use
phandles or direct look up via compatible strings

http://www.spinics.net/lists/arm-kernel/msg420847.html

and

http://lkml.iu.edu/hypermail/linux/kernel/1506.0/03787.html

There hasn't been a consensus since v1.

> 
> And as long as we have inconsistent use of soc_device, I don't want to 
> see any compatible strings related to it.
> 

Regards,
Sanchayan.