scsi: ufs: core: Fix abnormal scale up after scale down

When no active_reqs, devfreq_monitor (thread A) will suspend clock scaling.
But it may have racing with clk_scaling.suspend_work (thread B) and
actually not suspend clock scaling (requeue after suspend).  Next time
after polling_ms, devfreq_monitor read clk_scaling.window_start_t = 0 then
scale up clock abnormal.

Below is racing step:
	devfreq->work (Thread A)
	devfreq_monitor
		update_devfreq
		.....
			ufshcd_devfreq_target
			queue_work(hba->clk_scaling.workq,
1			   &hba->clk_scaling.suspend_work)
		.....
5	queue_delayed_work(devfreq_wq, &devfreq->work,
			msecs_to_jiffies(devfreq->profile->polling_ms));

2	hba->clk_scaling.suspend_work (Thread B)
	ufshcd_clk_scaling_suspend_work
		__ufshcd_suspend_clkscaling
			devfreq_suspend_device(hba->devfreq);
3				cancel_delayed_work_sync(&devfreq->work);
4			hba->clk_scaling.window_start_t = 0;
	.....

Signed-off-by: Peter Wang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Bart Van Assche <[email protected]>
Signed-off-by: Martin K. Petersen <[email protected]>

Author: ptr324

drivers/ufs/core/ufshcd.c

@@ -1402,6 +1402,13 @@ static int ufshcd_devfreq_target(struct device *dev,
 		return 0;
 	}
 
+	/* Skip scaling clock when clock scaling is suspended */
+	if (hba->clk_scaling.is_suspended) {
+		spin_unlock_irqrestore(hba->host->host_lock, irq_flags);
+		dev_warn(hba->dev, "clock scaling is suspended, skip");
+		return 0;
+	}
+
 	if (!hba->clk_scaling.active_reqs)
 		sched_clk_scaling_suspend_work = true;