[PATCH RFC] ufs: Make ufshcd_wait_for_register() sleep instead of busy-waiting

[Bart Van Assche <bvanassche@acm.org>]

The ufshcd_wait_for_register() function either sleeps or spins until the
specified register has reached the desired value. Busy-waiting is not
only considered a bad practice but also has a bad impact on energy
consumption. Always sleep instead of spinning by making sure that all
ufshcd_wait_for_register() calls happen from a context where it is
allowed to sleep. The only function call that has to be moved is the
ufshcd_hba_stop() call in ufshcd_host_reset_and_restore().

Cc: Can Guo <cang@codeaurora.org>
Cc: Avri Altman <avri.altman@wdc.com>
Cc: Bean Huo <beanhuo@micron.com>
Cc: Alim Akhtar <alim.akhtar@samsung.com>
Cc: Asutosh Das <asutoshd@codeaurora.org>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 drivers/scsi/ufs/ufshcd.c | 51 +++++++++++++++++++++------------------
 drivers/scsi/ufs/ufshcd.h |  2 +-
 2 files changed, 29 insertions(+), 24 deletions(-)

diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
index bf7caea2253b..72069d4faa1e 100644
--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -563,21 +563,21 @@ void ufshcd_delay_us(unsigned long us, unsigned long tolerance)
 }
 EXPORT_SYMBOL_GPL(ufshcd_delay_us);
 
-/*
+/**
  * ufshcd_wait_for_register - wait for register value to change
- * @hba - per-adapter interface
- * @reg - mmio register offset
- * @mask - mask to apply to read register value
- * @val - wait condition
- * @interval_us - polling interval in microsecs
- * @timeout_ms - timeout in millisecs
- * @can_sleep - perform sleep or just spin
+ * @hba: per-adapter interface
+ * @reg: mmio register offset
+ * @mask: mask to apply to the read register value
+ * @val: value to wait for
+ * @interval_us: polling interval in microseconds
+ * @timeout_ms: timeout in milliseconds
  *
- * Returns -ETIMEDOUT on error, zero on success
+ * Return:
+ * -ETIMEDOUT on error, zero on success.
  */
 int ufshcd_wait_for_register(struct ufs_hba *hba, u32 reg, u32 mask,
 				u32 val, unsigned long interval_us,
-				unsigned long timeout_ms, bool can_sleep)
+				unsigned long timeout_ms)
 {
 	int err = 0;
 	unsigned long timeout = jiffies + msecs_to_jiffies(timeout_ms);
@@ -586,10 +586,7 @@ int ufshcd_wait_for_register(struct ufs_hba *hba, u32 reg, u32 mask,
 	val = val & mask;
 
 	while ((ufshcd_readl(hba, reg) & mask) != val) {
-		if (can_sleep)
-			usleep_range(interval_us, interval_us + 50);
-		else
-			udelay(interval_us);
+		usleep_range(interval_us, interval_us + 50);
 		if (time_after(jiffies, timeout)) {
 			if ((ufshcd_readl(hba, reg) & mask) != val)
 				err = -ETIMEDOUT;
@@ -2589,7 +2586,7 @@ ufshcd_clear_cmd(struct ufs_hba *hba, int tag)
 	 */
 	err = ufshcd_wait_for_register(hba,
 			REG_UTP_TRANSFER_REQ_DOOR_BELL,
-			mask, ~mask, 1000, 1000, true);
+			mask, ~mask, 1000, 1000);
 
 	return err;
 }
@@ -4258,16 +4255,23 @@ EXPORT_SYMBOL_GPL(ufshcd_make_hba_operational);
 /**
  * ufshcd_hba_stop - Send controller to reset state
  * @hba: per adapter instance
- * @can_sleep: perform sleep or just spin
  */
-static inline void ufshcd_hba_stop(struct ufs_hba *hba, bool can_sleep)
+static inline void ufshcd_hba_stop(struct ufs_hba *hba)
 {
+	unsigned long flags;
 	int err;
 
+	/*
+	 * Obtain the host lock to prevent that the controller is disabled
+	 * while the UFS interrupt handler is active on another CPU.
+	 */
+	spin_lock_irqsave(hba->host->host_lock, flags);
 	ufshcd_writel(hba, CONTROLLER_DISABLE,  REG_CONTROLLER_ENABLE);
+	spin_unlock_irqrestore(hba->host->host_lock, flags);
+
 	err = ufshcd_wait_for_register(hba, REG_CONTROLLER_ENABLE,
 					CONTROLLER_ENABLE, CONTROLLER_DISABLE,
-					10, 1, can_sleep);
+					10, 1);
 	if (err)
 		dev_err(hba->dev, "%s: Controller disable failed\n", __func__);
 }
@@ -4288,7 +4292,7 @@ int ufshcd_hba_enable(struct ufs_hba *hba)
 
 	if (!ufshcd_is_hba_active(hba))
 		/* change controller state to "reset state" */
-		ufshcd_hba_stop(hba, true);
+		ufshcd_hba_stop(hba);
 
 	/* UniPro link is disabled at this point */
 	ufshcd_set_link_off(hba);
@@ -5911,7 +5915,7 @@ static int ufshcd_clear_tm_cmd(struct ufs_hba *hba, int tag)
 	/* poll for max. 1 sec to clear door bell register by h/w */
 	err = ufshcd_wait_for_register(hba,
 			REG_UTP_TASK_REQ_DOOR_BELL,
-			mask, 0, 1000, 1000, true);
+			mask, 0, 1000, 1000);
 out:
 	return err;
 }
@@ -6478,8 +6482,9 @@ static int ufshcd_host_reset_and_restore(struct ufs_hba *hba)
 	 * Stop the host controller and complete the requests
 	 * cleared by h/w
 	 */
+	ufshcd_hba_stop(hba);
+
 	spin_lock_irqsave(hba->host->host_lock, flags);
-	ufshcd_hba_stop(hba, false);
 	hba->silence_err_logs = true;
 	ufshcd_complete_requests(hba);
 	hba->silence_err_logs = false;
@@ -7986,7 +7991,7 @@ static int ufshcd_link_state_transition(struct ufs_hba *hba,
 		 * Change controller state to "reset state" which
 		 * should also put the link in off/reset state
 		 */
-		ufshcd_hba_stop(hba, true);
+		ufshcd_hba_stop(hba);
 		/*
 		 * TODO: Check if we need any delay to make sure that
 		 * controller is reset
@@ -8545,7 +8550,7 @@ void ufshcd_remove(struct ufs_hba *hba)
 	scsi_remove_host(hba->host);
 	/* disable interrupts */
 	ufshcd_disable_intr(hba, hba->intr_mask);
-	ufshcd_hba_stop(hba, true);
+	ufshcd_hba_stop(hba);
 
 	ufshcd_exit_clk_scaling(hba);
 	ufshcd_exit_clk_gating(hba);
diff --git a/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
index 733722840794..5c944530cde5 100644
--- a/drivers/scsi/ufs/ufshcd.h
+++ b/drivers/scsi/ufs/ufshcd.h
@@ -822,7 +822,7 @@ int ufshcd_uic_hibern8_exit(struct ufs_hba *hba);
 void ufshcd_delay_us(unsigned long us, unsigned long tolerance);
 int ufshcd_wait_for_register(struct ufs_hba *hba, u32 reg, u32 mask,
 				u32 val, unsigned long interval_us,
-				unsigned long timeout_ms, bool can_sleep);
+				unsigned long timeout_ms);
 void ufshcd_parse_dev_ref_clk_freq(struct ufs_hba *hba, struct clk *refclk);
 void ufshcd_update_reg_hist(struct ufs_err_reg_hist *reg_hist,
 			    u32 reg);