Re: [PATCH v4 1/2] i2c: qup: add ACPI support

Hi Arnd,

On 06/30/2016 07:52 AM, Arnd Bergmann wrote:

On Thursday, June 30, 2016 7:35:14 AM CEST Christopher Covington wrote:

quoted

Hi Arnd,

On 06/08/2016 05:02 PM, Arnd Bergmann wrote:

quoted

On Wednesday, June 8, 2016 12:19:44 PM CEST Austin Christ wrote:

quoted

+               ret = device_property_read_u32(qup->dev,
+                               "src-clock-hz", &src_clk_freq);
+               if (ret) {
+                       dev_warn(qup->dev, "using default src-clock-hz %d",
+                               DEFAULT_SRC_CLK);
+                       src_clk_freq = DEFAULT_SRC_CLK;
+               }

Where is this property documented?

We plan on submitting documentation via dsd@acpica.org to
https://github.com/ahs3/dsd once it is operational. As I understand it
the project is brand new. It may take several months to begin accepting
submissions. In the mean time, we could potentially include
documentation in a reply to this thread, the cover of the next series, a
wiki page on codeaurora.org, a file in Documentation (perhaps to be
replaced by ACPICA style imports of the OS-neutral DSD project or a git
submodule) or potentially other means. Please let us know what you think
is sufficient.

As you are reusing part of the DT binding, it seems appropriate to put
the documentation for this into the binding documentation in the kernel.

My understanding is that in the device tree case, the input/source clock
frequency is assumed to be run-time managed through Global Clock
Controller (GCC) code and the common clock framework.

drivers/i2c/busses/i2c-qup.c:1549

src_clk_freq = clk_get_rate(qup->clk);

So a given I2C device tree entry points to the GCC device tree entry,
but there isn't an explicit, fixed input/source clock frequency value.

arch/arm64/boot/dts/qcom/msm8916.dtsi:310

blsp_i2c2: i2c@78b6000 {
        compatible = "qcom,i2c-qup-v2.2.1";
        reg = <0x78b6000 0x1000>;
        interrupts = <GIC_SPI 96 0>;
        clocks = <&gcc GCC_BLSP1_AHB_CLK>,
                <&gcc GCC_BLSP1_QUP2_I2C_APPS_CLK>;
        clock-names = "iface", "core";
        pinctrl-names = "default", "sleep";
        pinctrl-0 = <&i2c2_default>;
        pinctrl-1 = <&i2c2_sleep>;
        #address-cells = <1>;
        #size-cells = <0>;
        status = "disabled";
};

On the other hand, when ACPI is in use, the driver assumes a fixed
input/source clock frequency value, which it tries to look up as a
device property.

(I'm out of my depth here, so somebody please correct me if I've
described this wrong.)

Thanks,
Cov

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