Re: [PATCH v9 1/3] scsi: ufs: Protect some contexts from unexpected clock scaling

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On 2021-01-13 18:14, 황두현 wrote:

From: Can Guo <cang@xxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxx>
---
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.


-EPERM is usually used by IOCTL to tell users that
they don't have right permissions. -EAGAIN here tells
the caller that if it tries again, it may success, i.e
after hba is runtime resumed or error recovery is completed.




+	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().
Check ufshcd_wait_for_doorbell_clr(), it calls ufshcd_hold/release() inside. 




+	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.


No, if hba is runtime suspended (rpm_lvl = 3/4/5),
calling ufshcd_hold() here shall fail, because you
are trying to exit hibern8 even when UFS is not
powered or VCCQ2/VCCQ in LPM.

So ufshcd_hold MUST come after hba->clk_scaling.is_allowed
check in prepare(), and the code is clean and tight if
ufshcd_hold() is put in prepare().




 	ret = ufshcd_clock_scaling_prepare(hba);
 	if (ret)


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



See my comments above.


-		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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