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Date:   Mon, 5 Nov 2018 17:04:26 -0800
From:   Bjorn Andersson <bjorn.andersson@linaro.org>
To:     Stephen Boyd <swboyd@chromium.org>
Cc:     Stephen Boyd <sboyd@kernel.org>,
        Michael Turquette <mturquette@baylibre.com>,
        linux-kernel@vger.kernel.org, linux-clk@vger.kernel.org,
        linux-arm-msm@vger.kernel.org, devicetree@vger.kernel.org,
        Rob Herring <robh+dt@kernel.org>,
        Taniya Das <tdas@codeaurora.org>
Subject: Re: [PATCH 1/2] dt-bindings: clk: Introduce 'protected-clocks'
 property
Message-ID: <20181106010426.GX2523@minitux>
References: <20181105194011.43770-1-swboyd@chromium.org>
 <20181105194011.43770-2-swboyd@chromium.org>
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On Mon 05 Nov 11:40 PST 2018, Stephen Boyd wrote:

> 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 <bjorn.andersson@linaro.org>

Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>

Regards,
Bjorn

> Cc: Taniya Das <tdas@codeaurora.org>
> Signed-off-by: Stephen Boyd <swboyd@chromium.org>
> ---
>  .../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>;
> +   };
> -- 
> Sent by a computer through tubes
>