linux-kernel - Re: [PATCH 3/3] soundwire: qcom: add wake up interrupt support

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Message-ID: <5e050d4c-e3d2-35fb-ca49-7be53579bc31@linux.intel.com>
Date:   Tue, 22 Feb 2022 13:26:57 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        robh+dt@...nel.org, vkoul@...nel.org,
        yung-chuan.liao@...ux.intel.com
Cc:     devicetree@...r.kernel.org, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, quic_srivasam@...cinc.com
Subject: Re: [PATCH 3/3] soundwire: qcom: add wake up interrupt support




> +static irqreturn_t qcom_swrm_wake_irq_handler(int irq, void *dev_id)
> +{
> +	struct qcom_swrm_ctrl *swrm = dev_id;
> +	int ret = IRQ_HANDLED;
> +	struct sdw_slave *slave;
> +
> +	clk_prepare_enable(swrm->hclk);
> +
> +	if (swrm->wake_irq > 0) {
> +		if (!irqd_irq_disabled(irq_get_irq_data(swrm->wake_irq)))
> +			disable_irq_nosync(swrm->wake_irq);
> +	}
> +
> +	/*
> +	 * resume all the slaves which must have potentially generated this
> +	 * interrupt, this should also wake the controller at the same time.
> +	 * this is much safer than waking controller directly that will deadlock!
> +	 */
There should be no difference if you first resume the controller and
then attached peripherals, or do a loop where you rely on the pm_runtime
framework.

The notion that there might be a dead-lock is surprising, you would need
to elaborate here.

> +	list_for_each_entry(slave, &swrm->bus.slaves, node) {
> +		ret = pm_runtime_get_sync(&slave->dev);

In my experience, you don't want to blur layers and take references on
the child devices from the parent device. I don't know how many times we
end-up with weird behavior.

we've done something similar on the Intel side but implemented in a less
directive manner.

ret = device_for_each_child(bus->dev, NULL, intel_resume_child_device);

static int intel_resume_child_device(struct device *dev, void *data)
{
[...]	
	ret = pm_request_resume(dev);
	if (ret < 0)
		dev_err(dev, "%s: pm_request_resume failed: %d\n", __func__, ret);

	return ret;
}


> +		if (ret < 0 && ret != -EACCES) {
> +			dev_err_ratelimited(swrm->dev,
> +					    "pm_runtime_get_sync failed in %s, ret %d\n",
> +					    __func__, ret);
> +			pm_runtime_put_noidle(&slave->dev);
> +			ret = IRQ_NONE;
> +			goto err;
> +		}
> +	}
> +
> +	list_for_each_entry(slave, &swrm->bus.slaves, node) {
> +		pm_runtime_mark_last_busy(&slave->dev);
> +		pm_runtime_put_autosuspend(&slave->dev);
> +	}
> +err:
> +	clk_disable_unprepare(swrm->hclk);
> +	return IRQ_HANDLED;
> +}
> +