Re: [RFC v3 08/14] MIPS: dts: qca: introduce AR9331 devicetree

[Antony Pavlov <antonynpavlov@gmail.com>]

On Mon, 25 Jan 2016 23:46:30 +0100
Alban <albeu@free.fr> wrote:

> On Sat, 23 Jan 2016 23:17:25 +0300
> Antony Pavlov <antonynpavlov@gmail.com> wrote:
> 
> > This patch introduces devicetree for Atheros AR9331 SoC (AKA Hornet).
> > The AR9331 chip is a Wi-Fi System-On-Chip (WiSOC),
> > typically used in very cheap Access Points and Routers.
> > 
> > Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
> > Cc: Gabor Juhos <juhosg@openwrt.org>
> > Cc: Alban Bedel <albeu@free.fr>
> > Cc: linux-mips@linux-mips.org
> > Cc: devicetree@vger.kernel.org
> > ---
> >  arch/mips/boot/dts/qca/ar9331.dtsi | 123 +++++++++++++++++++++++++++++++++++++
> >  1 file changed, 123 insertions(+)
> > 
> > diff --git a/arch/mips/boot/dts/qca/ar9331.dtsi b/arch/mips/boot/dts/qca/ar9331.dtsi
> > new file mode 100644
> > index 0000000..bf128a2
> > --- /dev/null
> > +++ b/arch/mips/boot/dts/qca/ar9331.dtsi
> > @@ -0,0 +1,123 @@
> > +#include <dt-bindings/clock/ath79-clk.h>
> > +
> > +/ {
> > +	compatible = "qca,ar9331";
> > +
> 
> [...]
> 
> > +
> > +	extosc: oscillator {
> > +		compatible = "fixed-clock";
> > +		#clock-cells = <0>;
> > +	};
> 
> This oscillator is on the board and not in the SoC, so it should
> be in the board DTS.

However oscillator is inside SoC!

Please see https://en.wikipedia.org/wiki/Electronic_oscillator

    An electronic oscillator is an electronic circuit that produces a periodic,
    oscillating electronic signal, often a sine wave or a square wave.

Please see AR9331 data sheet: the SoC has no input for external oscillator,
only two pins (XTALO and XTALI) for connecting 25 MHz or 40 MHz quartz crystal.
The crystal can't produce a square wave itself! The crystal is only a part
of a complete oscillator.

So we have a good reason to put basic oscillator node into the SoC dtsi-file.

-- 
Best regards,
  Antony Pavlov