Re: [PATCH 1/8] dt/bindings: firmware: Add Qualcomm SCM binding

Rob Herring
2016-04-25T13:14:20Z

On Sat, Apr 23, 2016 at 12:33:51PM -0500, Andy Gross wrote:
> On Sat, Apr 23, 2016 at 11:56:50AM -0500, Rob Herring wrote:
> > On Fri, Apr 22, 2016 at 5:17 PM, Andy Gross <andy.gross@linaro.org> wrote:
> > > This patch adds the device tree support for the Qualcomm SCM firmware.
> > >
> > > Signed-off-by: Andy Gross <andy.gross@linaro.org>
> > > ---
> > > .../devicetree/bindings/firmware/qcom,scm.txt | 31 ++++++++++++++++++++++
> > > 1 file changed, 31 insertions(+)
> > > create mode 100644 Documentation/devicetree/bindings/firmware/qcom,scm.txt
> > >
> > > diff --git a/Documentation/devicetree/bindings/firmware/qcom,scm.txt b/Documentation/devicetree/bindings/firmware/qcom,scm.txt
> > > new file mode 100644
> > > index 0000000..57b9b3a
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/firmware/qcom,scm.txt
> > > @@ -0,0 +1,31 @@
> > > +QCOM Secure Channel Manager (SCM)
> > > +
> > > +Qualcomm processors include an interface to communicate to the secure firmware.
> > > +This interface allows for clients to request different types of actions. These
> > > +can include CPU power up/down, HDCP requests, loading of firmware, and other
> > > +assorted actions.
> > > +
> > > +Required properties:
> > > +- compatible: must contain one of the following:
> > > + * "qcom,scm-apq8064" for APQ8064
> > > + * "qcom,scm-apq8084" for MSM8084
> > > + * "qcom,scm-msm8916" for MSM8916
> > > + * "qcom,scm-msm8974" for MSM8974
> > > +- clocks: One to three clocks may be required based on compatible.
> > > + * Only core clock required for "qcom,scm-apq8064"
> > > + * Core, iface, and bus clocks required for all other compatibles.
> > > +- clock-names: Must contain "core" for the core clock, "iface" for the interface
> > > + clock and "bus" for the bus clock per the requirements of the compatible.
> > > +
> > > +Example for MSM8916:
> > > +
> > > + firmware {
> > > + compatible = "simple-bus";
> >
> > Firmware is a bus? Really? Let's not put hacks in the DT just so you
> > get automatic probing.
>
> So something like:
>
> firmware {
> compatible = "qcom,scm-apq8084";
> clocks = <&gcc GCC_CE1_CLK> , <&gcc GCC_CE1_AXI_CLK>, <&gcc GCC_CE1_AHB_CLK>;
> clock-names = "core", "bus", "iface";
> };
>
> Seems to work fine.

Yes, because the top level nodes are probed. But then you can't have any
other firmware nodes. You are going to have to call of_platform_populate
on the /firmware node or create the device yourself. If there are other
users of /firmware needing to probe, then we can perhaps do it
generically.

> > > +
> > > + scm {
> > > + compatible = "qcom,scm-msm8916";
> > > + clocks = <&gcc GCC_CRYPTO_CLK> , <&gcc GCC_CRYPTO_AXI_CLK>, <&gcc GCC_CRYPTO_AHB_CLK>;
> > > + clock-names = "core", "bus", "iface";
> >
> > Generally, /firmware defines an interface to firmware. I don't think
> > clocks belong here. This implies that non-secure world can turn off
> > clocks to secure world?
>
> The caller into the SCM is on the hook for making sure the clocks are turned on.
> The firmware people decided to not manage the clocks. In a perfect world, they
> would turn on their own clocks and it would all be self contained. Sadly, it
> isn't going to change.

Okay. Seems like a security problem to me though.

Rob