Can't enable BCM2835 PCM clocks at boot up

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#3,564 1 comment 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
25/100
Issue type
Feature
Clarity
Needs clarification
Activity status
Stale
Tech stack
c, linux
Domain
embedded-iot, operating-systems

Research direction

Start with the BCM2835 I2S/PCM clock implementation and the device-tree overlay shown in the issue, then trace the devm_clk_get, clk_set_rate, and clk_prepare_enable calls used for the mclk. Determine whether boot-time PCM clock enablement is supported and define a reproducible test for confirming a continuous clock; the issue is complete only when that behavior works or a documented limitation is established.

Written by the indexing model from the issue text.

Description

Hi,

As for now there is no continuous I2S/PCM clock support on the I2S BCM2835 driver I'm trying to enable the clocks manually (without any succes until now) in the following way:

  • Define the clock in the device tree as:
    fragment@4 {
    target = <&sound>;
    overlay {
    compatible = "merus,merus-amp";
    i2s-controller = <&i2s>;
    status = "okay";
    pinctrl-names = "default";
    pinctrl-0 = <&gpio4_clk_pin>;
    clocks = <&clocks BCM2835_CLOCK_PCM >; /* BCM2835_CLOCK_GP0 */
    clock-names = "mclk";
    mute_gp-gpios = <&gpio 15 GPIO_ACTIVE_HIGH>;
    };
    };
  • Enable the clock (and parent if neccesary) as:
    priv_data->mclk = devm_clk_get(&pdev->dev, "mclk");
    clk_set_rate(priv_data->mclk, 2822400); //Trying an example frequency
    ret = clk_prepare_enable(priv_data->mclk2);

Altough I have no errors in the log the clock is never enabled. The only way I succed is using a general purpose clock, but not with the PCM clocks.

Is there any way to make this possible?

Best,
Ariel

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