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Date:   Fri, 18 Dec 2020 14:26:06 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Stanley Chu <stanley.chu@...iatek.com>
Cc:     asutoshd@...eaurora.org, nguyenb@...eaurora.org,
        hongwus@...eaurora.org, rnayak@...eaurora.org,
        linux-scsi@...r.kernel.org, kernel-team@...roid.com,
        saravanak@...gle.com, salyzyn@...gle.com,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Bean Huo <beanhuo@...ron.com>,
        Bart Van Assche <bvanassche@....org>,
        Satya Tangirala <satyat@...gle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/3] scsi: ufs: Protect some contexts from unexpected
 clock scaling

On 2020-12-15 13:43, Stanley Chu wrote:
> Hi Can,
> 
> On Sun, 2020-12-13 at 08:31 -0800, Can Guo wrote:
>> 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 sysfs node clkscale_enable and 
>> devfreq
>> sysfs nodes like min/max_freq and governor. Add one more flag in 
>> struct
>> clk_scaling such that these contexts can prevent clock scaling from 
>> being
>> invoked through above sysfs nodes.
>> 
>> Signed-off-by: Can Guo <cang@...eaurora.org>
>> ---
>>  drivers/scsi/ufs/ufshcd.c | 83 
>> +++++++++++++++++++++++++++++++----------------
>>  drivers/scsi/ufs/ufshcd.h |  2 ++
>>  2 files changed, 57 insertions(+), 28 deletions(-)
>> 
>> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
>> index 0c148fc..4ccdd2b 100644
>> --- a/drivers/scsi/ufs/ufshcd.c
>> +++ b/drivers/scsi/ufs/ufshcd.c
>> @@ -1147,12 +1147,22 @@ 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)) {
>> +
>> +	if (!hba->clk_scaling.is_allowed)
>> +		ret = -EAGAIN;
>> +	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;
>>  }
>> 
>> @@ -1160,6 +1170,7 @@ static void 
>> ufshcd_clock_scaling_unprepare(struct ufs_hba *hba)
>>  {
>>  	up_write(&hba->clk_scaling_lock);
>>  	ufshcd_scsi_unblock_requests(hba);
>> +	ufshcd_release(hba);
>>  }
>> 
>>  /**
>> @@ -1175,12 +1186,9 @@ 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);
>> -
>>  	ret = ufshcd_clock_scaling_prepare(hba);
>>  	if (ret)
>> -		goto out;
>> +		return ret;
>> 
>>  	/* scale down the gear before scaling down clocks */
>>  	if (!scale_up) {
>> @@ -1212,8 +1220,6 @@ static int ufshcd_devfreq_scale(struct ufs_hba 
>> *hba, bool scale_up)
>> 
>>  out_unprepare:
>>  	ufshcd_clock_scaling_unprepare(hba);
>> -out:
>> -	ufshcd_release(hba);
>>  	return ret;
>>  }
>> 
>> @@ -1487,7 +1493,7 @@ 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,
>> @@ -1496,12 +1502,20 @@ static ssize_t 
>> ufshcd_clkscale_enable_store(struct device *dev,
>>  	struct ufs_hba *hba = dev_get_drvdata(dev);
>>  	u32 value;
>>  	int err;
>> +	unsigned long flags;
>> +	bool update = true;
>> 
>>  	if (kstrtou32(buf, 0, &value))
>>  		return -EINVAL;
>> 
>>  	value = !!value;
>> -	if (value == hba->clk_scaling.is_allowed)
>> +	spin_lock_irqsave(hba->host->host_lock, flags);
>> +	if (value == hba->clk_scaling.is_enabled)
>> +		update = false;
>> +	else
>> +		hba->clk_scaling.is_enabled = value;
>> +	spin_unlock_irqrestore(hba->host->host_lock, flags);
>> +	if (!update)
>>  		goto out;
>> 
>>  	pm_runtime_get_sync(hba->dev);
>> @@ -1510,8 +1524,6 @@ 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;
>> -
>>  	if (value) {
>>  		ufshcd_resume_clkscaling(hba);
>>  	} else {
>> @@ -1845,8 +1857,6 @@ 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)
>> @@ -1854,6 +1864,8 @@ static void ufshcd_exit_clk_scaling(struct 
>> ufs_hba *hba)
>>  	if (!ufshcd_is_clkscaling_supported(hba))
>>  		return;
>> 
>> +	if (hba->devfreq)
>> +		device_remove_file(hba->dev, &hba->clk_scaling.enable_attr);
>>  	destroy_workqueue(hba->clk_scaling.workq);
>>  	ufshcd_devfreq_remove(hba);
>>  }
>> @@ -1918,7 +1930,7 @@ 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)
>> @@ -4987,7 +4999,8 @@ static void __ufshcd_transfer_req_compl(struct 
>> ufs_hba *hba,
>>  				complete(hba->dev_cmd.complete);
>>  			}
>>  		}
>> -		if (ufshcd_is_clkscaling_supported(hba))
>> +		if (ufshcd_is_clkscaling_supported(hba) &&
>> +		    hba->clk_scaling.active_reqs > 0)
>>  			hba->clk_scaling.active_reqs--;
>>  	}
>> 
>> @@ -5650,18 +5663,25 @@ static void ufshcd_err_handling_prepare(struct 
>> ufs_hba *hba)
>>  		ufshcd_vops_resume(hba, UFS_RUNTIME_PM);
>>  	} 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);
>>  }
>> @@ -7620,12 +7640,14 @@ 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;
> 
> Perhaps moving this line after ufshcd_devfreq_init() is successful?

devfreq starts to work even before ufshcd_devfreq_init() returns,
I don't want to block it, hence put it before ufshcd_devfreq_init().
If devfreq fails to initialize, clk_scaling and its related sysfs
nodes anyways won't work and clk_scaling->is_enabled is false, so
we are safe.

> 
>>  			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);
>> @@ -8491,11 +8513,14 @@ 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) {
>> @@ -8592,8 +8617,6 @@ 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);
>>  	if (ufshcd_is_link_hibern8(hba) && !ufshcd_uic_hibern8_exit(hba))
>>  		ufshcd_set_link_active(hba);
>> @@ -8603,7 +8626,10 @@ 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;
>> @@ -8701,7 +8727,10 @@ 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 */
>> @@ -8725,8 +8754,6 @@ 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;
>> @@ -8915,6 +8942,8 @@ int ufshcd_shutdown(struct ufs_hba *hba)
>> 
>>  	pm_runtime_get_sync(hba->dev);
>> 
>> +	ufshcd_exit_clk_scaling(hba);
>> +
>>  	ret = ufshcd_suspend(hba, UFS_SHUTDOWN_PM);
>>  out:
>>  	if (ret)
>> @@ -8944,8 +8973,6 @@ 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 e0f00a4..9fcecba 100644
>> --- a/drivers/scsi/ufs/ufshcd.h
>> +++ b/drivers/scsi/ufs/ufshcd.h
>> @@ -382,6 +382,7 @@ struct ufs_saved_pwr_info {
>>   * @workq: workqueue to schedule devfreq suspend/resume work
>>   * @suspend_work: worker to suspend devfreq
>>   * @resume_work: worker to resume devfreq
>> + * @is_enabled: tracks if scaling is currently enabled or not
>>   * @is_allowed: tracks if scaling is currently allowed or not
>>   * @is_busy_started: tracks if busy period has started or not
>>   * @is_suspended: tracks if devfreq is suspended or not
>> @@ -396,6 +397,7 @@ struct ufs_clk_scaling {
>>  	struct workqueue_struct *workq;
>>  	struct work_struct suspend_work;
>>  	struct work_struct resume_work;
>> +	bool is_enabled;
>>  	bool is_allowed;
>>  	bool is_busy_started;
>>  	bool is_suspended;
> 
> Now there are more and more "similar boolean attributes" regarding
> clk-scaling control, maybe add more comprehensive comments to describe
> them?
> 
> Otherwise this patch looks good to me.

Sure, I will give more words to the new flag.

Thanks,

Can Guo.

> 
> Feel free to add
> Reviewed-by: Stanley Chu <stanley.chu@...iatek.com>

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