Re: [PATCH 1/2] dt-bindings: clk: Introduce 'protected-clocks' property

On Mon 05 Nov 17:04 PST 2018, Bjorn Andersson wrote:

On Mon 05 Nov 11:40 PST 2018, Stephen Boyd wrote:

quoted

Add a generic clk property for clks which are not intended to be used by
the OS due to security restrictions put in place by firmware. For
example, on some Qualcomm firmwares reading or writing certain clk
registers causes the entire system to reboot, but on other firmwares
reading and writing those same registers is required to make devices
like QSPI work. Rather than adding one-off properties each time a new
set of clks appears to be protected, let's add a generic clk property to
describe any set of clks that shouldn't be touched by the OS. This way
we never need to register the clks or use them in certain firmware
configurations.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Bjorn Andersson <redacted>

Reviewed-by: Bjorn Andersson <redacted>

Gave this some additional thought. The way this is blacklisting
protected clocks makes it impossible to be backwards compatible with an
older DT while adding new protected clocks to an existing driver.

I don't have better suggestion for handling this and the problem should
primarily be isolated to the beginning of the upstream life of a
platform, so perhaps we can just ignore this issue?

Regards,
Bjorn

Regards,
Bjorn

quoted

Cc: Taniya Das <redacted>
Signed-off-by: Stephen Boyd <redacted>
---
 .../devicetree/bindings/clock/clock-bindings.txt | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/Documentation/devicetree/bindings/clock/clock-bindings.txt b/Documentation/devicetree/bindings/clock/clock-bindings.txt
index 2ec489eebe72..b646bbcf7f92 100644
--- a/Documentation/devicetree/bindings/clock/clock-bindings.txt
+++ b/Documentation/devicetree/bindings/clock/clock-bindings.txt

@@ -168,3 +168,19 @@ a shared clock is forbidden.
 
 Configuration of common clocks, which affect multiple consumer devices can
 be similarly specified in the clock provider node.
+
+==Protected clocks==
+
+Some platforms or firmwares may not fully expose all the clocks to the OS, such
+as in situations where those clks are used by drivers running in ARM secure
+execution levels. Such a configuration can be specified in device tree with the
+protected-clocks property in the form of a clock specifier list. This property should
+only be specified in the node that is providing the clocks being protected:
+
+   clock-controller@a000f000 {
+        compatible = "vendor,clk95;
+        reg = <0xa000f000 0x1000>
+        #clocks-cells = <1>;
+        ...
+        protected-clocks = <UART3_CLK>, <SPI5_CLK>;
+   };

-- 
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