Date:   Wed, 13 Jan 2021 19:14:37 +0900
From:   황두현 <dh0421.hwang@...sung.com>
To:     <cang@...eaurora.org>
Cc:     <adrian.hunter@...el.com>, <alim.akhtar@...sung.com>,
        <asutoshd@...eaurora.org>, <avri.altman@....com>,
        <beanhuo@...ron.com>, <hongwus@...eaurora.org>,
        <jejb@...ux.ibm.com>, <kernel-team@...roid.com>,
        <linux-kernel@...r.kernel.org>, <linux-scsi@...r.kernel.org>,
        <martin.petersen@...cle.com>, <nguyenb@...eaurora.org>,
        <rnayak@...eaurora.org>, <salyzyn@...gle.com>,
        <saravanak@...gle.com>, <satyat@...gle.com>,
        <stanley.chu@...iatek.com>, <grant.jung@...sung.com>,
        <jt77.jang@...sung.com>, <junwoo80.lee@...sung.com>,
        <dh0421.hwang@...sung.com>, <sh043.lee@...sung.com>,
        <jangsub.yi@...sung.com>, <cw9316.lee@...sung.com>,
        <sh8267.baek@...sung.com>, <wkon.kim@...sung.com>
Subject: Re: [PATCH v9 1/3] scsi: ufs: Protect some contexts from unexpected
 clock scaling

> From: Can Guo <cang@...eaurora.org>
> 
> In contexts like suspend, shutdown and error handling, we need to suspend
> devfreq to make sure these contexts won't be disturbed by clock scaling.
> However, suspending devfreq is not enough since users can still trigger a
> clock scaling by manipulating the devfreq sysfs nodes like min/max_freq and
> governor even after devfreq is suspended. Moreover, mere suspending devfreq
> cannot synchroinze a clock scaling which has already been invoked through
> these sysfs nodes. Add one more flag in struct clk_scaling and wrap the
> entire func ufshcd_devfreq_scale() with the clk_scaling_lock, so that we
> can use this flag and clk_scaling_lock to control and synchronize clock
> scaling invoked through devfreq sysfs nodes.
> 
> Signed-off-by: Can Guo <cang@...eaurora.org>
> ---
>  drivers/scsi/ufs/ufshcd.c | 86 +++++++++++++++++++++++++++++------------------
>  drivers/scsi/ufs/ufshcd.h |  6 +++-
>  2 files changed, 59 insertions(+), 33 deletions(-)
> 
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index 82ad317..64218e6 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -1181,19 +1181,33 @@ static int ufshcd_clock_scaling_prepare(struct ufs_hba *hba)
>  	 */
>  	ufshcd_scsi_block_requests(hba);
>  	down_write(&hba->clk_scaling_lock);
> -	if (ufshcd_wait_for_doorbell_clr(hba, DOORBELL_CLR_TOUT_US)) {
> +

I think another value is better than -EAGAIN.
Ex) -EPERM because the clk scaling is not allowed state.

> +	if (!hba->clk_scaling.is_allowed)
> +		ret = -EAGAIN;

I think ufshcd_hold() has to be called before access host registers,
so calling ufshcd_hold() is better before calling ufshcd_clock_scaling_prepare().

If you want to do not anything when hba->clk_scaling.is_allowed is false,
it is recommended to check hba->clk_scaling.is_allowed before calling ufshcd_hold() in ufshcd_devfreq_scale().

> +	else if (ufshcd_wait_for_doorbell_clr(hba, DOORBELL_CLR_TOUT_US))
>  		ret = -EBUSY;
> +
> +	if (ret) {
>  		up_write(&hba->clk_scaling_lock);
>  		ufshcd_scsi_unblock_requests(hba);
> +		goto out;
>  	}
>  
> +	/* let's not get into low power until clock scaling is completed */
> +	ufshcd_hold(hba, false);
> +
> +out:
>  	return ret;
>  }
>  
> -static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba)
> +static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba, bool writelock)
>  {
> -	up_write(&hba->clk_scaling_lock);
> +	if (writelock)
> +		up_write(&hba->clk_scaling_lock);
> +	else
> +		up_read(&hba->clk_scaling_lock);
>  	ufshcd_scsi_unblock_requests(hba);
> +	ufshcd_release(hba);
>  }
>  
>  /**
> @@ -1208,13 +1222,11 @@ static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba)
>  static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up)
>  {
>  	int ret = 0;
> -
> -	/* let's not get into low power until clock scaling is completed */
> -	ufshcd_hold(hba, false);
> +	bool is_writelock = true;
>  

I think it would be nice to call ufshcd_hold() here.

>  	ret = ufshcd_clock_scaling_prepare(hba);
>  	if (ret)

Below change is not needed if calling ufshcd_hold() is before calling ufshcd_clock_scaling_prepare().

> -		goto out;
> +		return ret;
>  
>  	/* scale down the gear before scaling down clocks */
>  	if (!scale_up) {
> @@ -1240,14 +1252,12 @@ static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up)
>  	}
>  
>  	/* Enable Write Booster if we have scaled up else disable it */
> -	up_write(&hba->clk_scaling_lock);
> +	downgrade_write(&hba->clk_scaling_lock);
> +	is_writelock = false;
>  	ufshcd_wb_ctrl(hba, scale_up);
> -	down_write(&hba->clk_scaling_lock);
>  
>  out_unprepare:
> -	ufshcd_clock_scaling_unprepare(hba);
> -out:
> -	ufshcd_release(hba);
> +	ufshcd_clock_scaling_unprepare(hba, is_writelock);
>  	return ret;
>  }
>  
> @@ -1521,7 +1531,7 @@ static ssize_t ufshcd_clkscale_enable_show(struct device *dev,
>  {
>  	struct ufs_hba *hba = dev_get_drvdata(dev);
>  
> -	return snprintf(buf, PAGE_SIZE, "%d\n", hba->clk_scaling.is_allowed);
> +	return snprintf(buf, PAGE_SIZE, "%d\n", hba->clk_scaling.is_enabled);
>  }
>  
>  static ssize_t ufshcd_clkscale_enable_store(struct device *dev,
> @@ -1535,7 +1545,7 @@ static ssize_t ufshcd_clkscale_enable_store(struct device *dev,
>  		return -EINVAL;
>  
>  	value = !!value;
> -	if (value == hba->clk_scaling.is_allowed)
> +	if (value == hba->clk_scaling.is_enabled)
>  		goto out;
>  
>  	pm_runtime_get_sync(hba->dev);
> @@ -1544,7 +1554,7 @@ static ssize_t ufshcd_clkscale_enable_store(struct device *dev,
>  	cancel_work_sync(&hba->clk_scaling.suspend_work);
>  	cancel_work_sync(&hba->clk_scaling.resume_work);
>  
> -	hba->clk_scaling.is_allowed = value;
> +	hba->clk_scaling.is_enabled = value;
>  
>  	if (value) {
>  		ufshcd_resume_clkscaling(hba);
> @@ -1882,8 +1892,6 @@ static void ufshcd_init_clk_scaling(struct ufs_hba *hba)
>  	snprintf(wq_name, sizeof(wq_name), "ufs_clkscaling_%d",
>  		 hba->host->host_no);
>  	hba->clk_scaling.workq = create_singlethread_workqueue(wq_name);
> -
> -	ufshcd_clkscaling_init_sysfs(hba);
>  }
>  
>  static void ufshcd_exit_clk_scaling(struct ufs_hba *hba)
> @@ -1891,6 +1899,8 @@ static void ufshcd_exit_clk_scaling(struct ufs_hba *hba)
>  	if (!ufshcd_is_clkscaling_supported(hba))
>  		return;
>  
> +	if (hba->clk_scaling.enable_attr.attr.name)
> +		device_remove_file(hba->dev, &hba->clk_scaling.enable_attr);
>  	destroy_workqueue(hba->clk_scaling.workq);
>  	ufshcd_devfreq_remove(hba);
>  }
> @@ -1955,7 +1965,7 @@ static void ufshcd_clk_scaling_start_busy(struct ufs_hba *hba)
>  	if (!hba->clk_scaling.active_reqs++)
>  		queue_resume_work = true;
>  
> -	if (!hba->clk_scaling.is_allowed || hba->pm_op_in_progress)
> +	if (!hba->clk_scaling.is_enabled || hba->pm_op_in_progress)
>  		return;
>  
>  	if (queue_resume_work)
> @@ -5071,7 +5081,8 @@ static void __ufshcd_transfer_req_compl(struct ufs_hba *hba,
>  				update_scaling = true;
>  			}
>  		}
> -		if (ufshcd_is_clkscaling_supported(hba) && update_scaling)
> +		if (ufshcd_is_clkscaling_supported(hba) && update_scaling &&
> +		    hba->clk_scaling.active_reqs > 0)
>  			hba->clk_scaling.active_reqs--;
>  	}
>  
> @@ -5737,18 +5748,24 @@ static void ufshcd_err_handling_prepare(struct ufs_hba *hba)
>  		ufshcd_vops_resume(hba, pm_op);
>  	} else {
>  		ufshcd_hold(hba, false);
> -		if (hba->clk_scaling.is_allowed) {
> +		if (hba->clk_scaling.is_enabled) {
>  			cancel_work_sync(&hba->clk_scaling.suspend_work);
>  			cancel_work_sync(&hba->clk_scaling.resume_work);
>  			ufshcd_suspend_clkscaling(hba);
>  		}
> +		down_write(&hba->clk_scaling_lock);
> +		hba->clk_scaling.is_allowed = false;
> +		up_write(&hba->clk_scaling_lock);
>  	}
>  }
>  
>  static void ufshcd_err_handling_unprepare(struct ufs_hba *hba)
>  {
>  	ufshcd_release(hba);
> -	if (hba->clk_scaling.is_allowed)
> +	down_write(&hba->clk_scaling_lock);
> +	hba->clk_scaling.is_allowed = true;
> +	up_write(&hba->clk_scaling_lock);
> +	if (hba->clk_scaling.is_enabled)
>  		ufshcd_resume_clkscaling(hba);
>  	pm_runtime_put(hba->dev);
>  }
> @@ -7728,12 +7745,14 @@ static int ufshcd_add_lus(struct ufs_hba *hba)
>  			sizeof(struct ufs_pa_layer_attr));
>  		hba->clk_scaling.saved_pwr_info.is_valid = true;
>  		if (!hba->devfreq) {
> +			hba->clk_scaling.is_allowed = true;
>  			ret = ufshcd_devfreq_init(hba);
>  			if (ret)
>  				goto out;
> -		}
>  
> -		hba->clk_scaling.is_allowed = true;
> +			hba->clk_scaling.is_enabled = true;
> +			ufshcd_clkscaling_init_sysfs(hba);
> +		}
>  	}
>  
>  	ufs_bsg_probe(hba);
> @@ -8650,11 +8669,14 @@ static int ufshcd_suspend(struct ufs_hba *hba, enum ufs_pm_op pm_op)
>  	ufshcd_hold(hba, false);
>  	hba->clk_gating.is_suspended = true;
>  
> -	if (hba->clk_scaling.is_allowed) {
> +	if (hba->clk_scaling.is_enabled) {
>  		cancel_work_sync(&hba->clk_scaling.suspend_work);
>  		cancel_work_sync(&hba->clk_scaling.resume_work);
>  		ufshcd_suspend_clkscaling(hba);
>  	}
> +	down_write(&hba->clk_scaling_lock);
> +	hba->clk_scaling.is_allowed = false;
> +	up_write(&hba->clk_scaling_lock);
>  
>  	if (req_dev_pwr_mode == UFS_ACTIVE_PWR_MODE &&
>  			req_link_state == UIC_LINK_ACTIVE_STATE) {
> @@ -8751,8 +8773,6 @@ static int ufshcd_suspend(struct ufs_hba *hba, enum ufs_pm_op pm_op)
>  	goto out;
>  
>  set_link_active:
> -	if (hba->clk_scaling.is_allowed)
> -		ufshcd_resume_clkscaling(hba);
>  	ufshcd_vreg_set_hpm(hba);
>  	/*
>  	 * Device hardware reset is required to exit DeepSleep. Also, for
> @@ -8776,7 +8796,10 @@ static int ufshcd_suspend(struct ufs_hba *hba, enum ufs_pm_op pm_op)
>  	if (!ufshcd_set_dev_pwr_mode(hba, UFS_ACTIVE_PWR_MODE))
>  		ufshcd_disable_auto_bkops(hba);
>  enable_gating:
> -	if (hba->clk_scaling.is_allowed)
> +	down_write(&hba->clk_scaling_lock);
> +	hba->clk_scaling.is_allowed = true;
> +	up_write(&hba->clk_scaling_lock);
> +	if (hba->clk_scaling.is_enabled)
>  		ufshcd_resume_clkscaling(hba);
>  	hba->clk_gating.is_suspended = false;
>  	hba->dev_info.b_rpm_dev_flush_capable = false;
> @@ -8879,7 +8902,10 @@ static int ufshcd_resume(struct ufs_hba *hba, enum ufs_pm_op pm_op)
>  
>  	hba->clk_gating.is_suspended = false;
>  
> -	if (hba->clk_scaling.is_allowed)
> +	down_write(&hba->clk_scaling_lock);
> +	hba->clk_scaling.is_allowed = true;
> +	up_write(&hba->clk_scaling_lock);
> +	if (hba->clk_scaling.is_enabled)
>  		ufshcd_resume_clkscaling(hba);
>  
>  	/* Enable Auto-Hibernate if configured */
> @@ -8903,8 +8929,6 @@ static int ufshcd_resume(struct ufs_hba *hba, enum ufs_pm_op pm_op)
>  	ufshcd_vreg_set_lpm(hba);
>  disable_irq_and_vops_clks:
>  	ufshcd_disable_irq(hba);
> -	if (hba->clk_scaling.is_allowed)
> -		ufshcd_suspend_clkscaling(hba);
>  	ufshcd_setup_clocks(hba, false);
>  	if (ufshcd_is_clkgating_allowed(hba)) {
>  		hba->clk_gating.state = CLKS_OFF;
> @@ -9131,8 +9155,6 @@ void ufshcd_remove(struct ufs_hba *hba)
>  
>  	ufshcd_exit_clk_scaling(hba);
>  	ufshcd_exit_clk_gating(hba);
> -	if (ufshcd_is_clkscaling_supported(hba))
> -		device_remove_file(hba->dev, &hba->clk_scaling.enable_attr);
>  	ufshcd_hba_exit(hba);
>  }
>  EXPORT_SYMBOL_GPL(ufshcd_remove);
> diff --git a/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
> index aa9ea35..2863af1 100644
> --- a/drivers/scsi/ufs/ufshcd.h
> +++ b/drivers/scsi/ufs/ufshcd.h
> @@ -419,7 +419,10 @@ struct ufs_saved_pwr_info {
>   * @suspend_work: worker to suspend devfreq
>   * @resume_work: worker to resume devfreq
>   * @min_gear: lowest HS gear to scale down to
> - * @is_allowed: tracks if scaling is currently allowed or not
> + * @is_enabled: tracks if scaling is currently enabled or not, controlled by
> +		clkscale_enable sysfs node
> + * @is_allowed: tracks if scaling is currently allowed or not, used to block
> +		clock scaling which is not invoked from devfreq governor
>   * @is_busy_started: tracks if busy period has started or not
>   * @is_suspended: tracks if devfreq is suspended or not
>   */
> @@ -434,6 +437,7 @@ struct ufs_clk_scaling {
>  	struct work_struct suspend_work;
>  	struct work_struct resume_work;
>  	u32 min_gear;
> +	bool is_enabled;
>  	bool is_allowed;
>  	bool is_busy_started;
>  	bool is_suspended;
> -- 
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.

--
DooHyun Hwang
Samsung Electronics

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