netdev - Re: [PATCH net-next v5 12/13] net: wwan: t7xx: Device deep sleep lock/unlock

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Date:   Thu, 10 Mar 2022 12:21:31 +0200 (EET)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Ricardo Martinez <ricardo.martinez@...ux.intel.com>
cc:     Netdev <netdev@...r.kernel.org>, linux-wireless@...r.kernel.org,
        kuba@...nel.org, davem@...emloft.net, johannes@...solutions.net,
        ryazanov.s.a@...il.com, loic.poulain@...aro.org,
        m.chetan.kumar@...el.com, chandrashekar.devegowda@...el.com,
        linuxwwan@...el.com, chiranjeevi.rapolu@...ux.intel.com,
        haijun.liu@...iatek.com, amir.hanania@...el.com,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        dinesh.sharma@...el.com, eliot.lee@...el.com,
        moises.veleta@...el.com, pierre-louis.bossart@...el.com,
        muralidharan.sethuraman@...el.com, Soumya.Prakash.Mishra@...el.com,
        sreehari.kancharla@...el.com, madhusmita.sahu@...el.com
Subject: Re: [PATCH net-next v5 12/13] net: wwan: t7xx: Device deep sleep
 lock/unlock

On Wed, 23 Feb 2022, Ricardo Martinez wrote:

> From: Haijun Liu <haijun.liu@...iatek.com>
> 
> Introduce the mechanism to lock/unlock the device 'deep sleep' mode.
> When the PCIe link state is L1.2 or L2, the host side still can keep
> the device is in D0 state from the host side point of view. At the same
> time, if the device's 'deep sleep' mode is unlocked, the device will
> go to 'deep sleep' while it is still in D0 state on the host side.
> 
> Signed-off-by: Haijun Liu <haijun.liu@...iatek.com>
> Signed-off-by: Chandrashekar Devegowda <chandrashekar.devegowda@...el.com>
> Co-developed-by: Ricardo Martinez <ricardo.martinez@...ux.intel.com>
> Signed-off-by: Ricardo Martinez <ricardo.martinez@...ux.intel.com>
> ---



> +int t7xx_pci_sleep_disable_complete(struct t7xx_pci_dev *t7xx_dev)
> +{
> +	struct device *dev = &t7xx_dev->pdev->dev;
> +	int ret;
> +
> +	ret = wait_for_completion_timeout(&t7xx_dev->sleep_lock_acquire,
> +					  msecs_to_jiffies(PM_SLEEP_DIS_TIMEOUT_MS));
> +	if (!ret)
> +		dev_err_ratelimited(dev, "Resource wait complete timed out\n");
> +
> +	return ret;
> +}
> +
> +/**
> + * t7xx_pci_disable_sleep() - Disable deep sleep capability.
> + * @t7xx_dev: MTK device.
> + *
> + * Lock the deep sleep capability, note that the device can still go into deep sleep
> + * state while device is in D0 state, from the host's point-of-view.
> + *
> + * If device is in deep sleep state, wake up the device and disable deep sleep capability.
> + */
> +void t7xx_pci_disable_sleep(struct t7xx_pci_dev *t7xx_dev)
> +{
> +	unsigned long flags;
> +
> +	if (atomic_read(&t7xx_dev->md_pm_state) < MTK_PM_RESUMED) {
> +		atomic_inc(&t7xx_dev->sleep_disable_count);
> +		complete_all(&t7xx_dev->sleep_lock_acquire);
> +		return;
> +	}
> +
> +	spin_lock_irqsave(&t7xx_dev->md_pm_lock, flags);
> +	if (atomic_inc_return(&t7xx_dev->sleep_disable_count) == 1) {
> +		u32 deep_sleep_enabled;
> +
> +		reinit_completion(&t7xx_dev->sleep_lock_acquire);

You might want to check that there's a mechanism that prevents this 
racing with wait_for_completion_timeout() in t7xx_pci_sleep_disable_complete().

I couldn't prove it myself but there are probably aspect in the PM side of 
things I wasn't able to take fully into account (that is, which call 
paths are not possible to occur).

> +		t7xx_dev_set_sleep_capability(t7xx_dev, false);
> +
> +		deep_sleep_enabled = ioread32(IREG_BASE(t7xx_dev) + T7XX_PCIE_RESOURCE_STATUS);
> +		deep_sleep_enabled &= T7XX_PCIE_RESOURCE_STS_MSK;
> +		if (deep_sleep_enabled) {
> +			spin_unlock_irqrestore(&t7xx_dev->md_pm_lock, flags);
> +			complete_all(&t7xx_dev->sleep_lock_acquire);
> +			return;
> +		}
> +
> +		t7xx_mhccif_h2d_swint_trigger(t7xx_dev, H2D_CH_DS_LOCK);
> +	}
> +	spin_unlock_irqrestore(&t7xx_dev->md_pm_lock, flags);
> +}


-- 
 i.