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

[maitysanchayan]

Hello Rob,

On 16-05-24 12:09:41, Rob Herring wrote:
> On Mon, May 23, 2016 at 11:14 PM,  <maitysanchayan@xxxxxxxxx> wrote:
> > 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@colibri-vf:~# cd /sys/bus/soc/devices/soc0
> >> > root@colibri-vf:/sys/bus/soc/devices/soc0# ls
> >> > family     machine    power      revision   soc_id     subsystem  uevent
> >> > root@colibri-vf:/sys/bus/soc/devices/soc0# cat family
> >> > Freescale Vybrid VF610
> >> > root@colibri-vf:/sys/bus/soc/devices/soc0# cat machine
> >> > Freescale Vybrid
> >> > root@colibri-vf:/sys/bus/soc/devices/soc0# cat revision
> >> > 00000013
> >> > root@colibri-vf:/sys/bus/soc/devices/soc0# cat soc_id
> >> > df6472a6130f29d4
> >> >
> >> > Signed-off-by: Sanchayan Maity <maitysanchayan@xxxxxxxxx>
> >> > ---
> >> >  .../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
> 
> Yes, everyone wants to move all platform devices in the kernel to a
> corresponding DT node. The result is often making up nodes to do this.
> It's the same thing with cpufreq.
> 
> > and then it was recommended to migrate this to drivers/soc where we did use
> > phandles or direct look up via compatible strings
> 
> The location in the tree is an orthogonal issue. You could move it and
> use of_machine_is_compatible without any DT change.
> 
> The primary issue I have here is how do we bind soc_bus to DT in a
> consistent way. Sorry, but vybrid specific patches alone are never
> going to solve that issue.
> 
> > 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.
> 
> I actually prefer your previous version binding soc_bus to the root
> bus node to this version. I think that is closer to the right
> direction. 

So if I understand correctly, the binding at the SoC level is fine.
Keeping that but removing the additional made-up properties, viz. below

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"

would be fine?

We would have something similar to here
http://www.spinics.net/lists/devicetree/msg80655.html

but now with the DT binding under SoC bus.

Regards,
Sanchayan.

> After all, pretty much everything is an SOC and every SOC
> has an SOC bus. Pretty much every SOC and board have revisions and may
> need to expose that revision info as well. We have to do this
> consistently which means having a default implementation for
> simple-bus that is not opt-in.
> 
> Alternatively, we should just deprecate soc_bus and come up a
> different solution. Either way, I think we have a half implemented
> solution currently.
> 
> Rob