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

"Asutosh Das (asd)" <asutoshd@xxxxxxxxxxxxxx> · Fri, 8 May 2020 09:27:50 -0700

On 5/7/2020 3:27 PM, Bart Van Assche wrote:
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@xxxxxxxxxxxxxx>
Cc: Avri Altman <avri.altman@xxxxxxx>
Cc: Bean Huo <beanhuo@xxxxxxxxxx>
Cc: Alim Akhtar <alim.akhtar@xxxxxxxxxxx>
Cc: Asutosh Das <asutoshd@xxxxxxxxxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
Reviewed-by: Asutosh Das <asutoshd@xxxxxxxxxxxxxx>


  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);



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