[PATCH v3] ufs: core: fix lockdep warning of clk_scaling_lock

[peter.wang at mediatek.com]

From: Peter Wang <peter.wang at mediatek.com>

There have a lockdep warning like below in current flow.
kworker/u16:0:  Possible unsafe locking scenario:

kworker/u16:0:        CPU0                    CPU1
kworker/u16:0:        ----                    ----
kworker/u16:0:   lock(&hba->clk_scaling_lock);
kworker/u16:0:                                lock(&hba->dev_cmd.lock);
kworker/u16:0:                                lock(&hba->clk_scaling_lock);
kworker/u16:0:   lock(&hba->dev_cmd.lock);
kworker/u16:0:

Before this patch clk_scaling_lock was held in reader mode during the ufshcd_wb_toggle() call.
With this patch applied clk_scaling_lock is not held while ufshcd_wb_toggle() is called.

This is safe because ufshcd_wb_toggle will held clk_scaling_lock in reader mode "again" in flow
ufshcd_wb_toggle -> __ufshcd_wb_toggle -> ufshcd_query_flag_retry -> ufshcd_query_flag ->
ufshcd_exec_dev_cmd -> down_read(&hba->clk_scaling_lock);
The protect should enough and make sure clock is not change while send command.

ufshcd_wb_toggle can protected by hba->clk_scaling.is_allowed to make sure
ufshcd_devfreq_scale function not run concurrently.

Fixes: 0e9d4ca43ba8 ("scsi: ufs: Protect some contexts from unexpected clock scaling")
Signed-off-by: Peter Wang <peter.wang at mediatek.com>
---
 drivers/ufs/core/ufshcd.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index c7b337480e3e..aa57126fdb49 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -272,6 +272,7 @@ static void ufshcd_wb_toggle_flush_during_h8(struct ufs_hba *hba, bool set);
 static inline void ufshcd_wb_toggle_flush(struct ufs_hba *hba, bool enable);
 static void ufshcd_hba_vreg_set_lpm(struct ufs_hba *hba);
 static void ufshcd_hba_vreg_set_hpm(struct ufs_hba *hba);
+static void ufshcd_clk_scaling_allow(struct ufs_hba *hba, bool allow);
 
 static inline void ufshcd_enable_irq(struct ufs_hba *hba)
 {
@@ -1249,12 +1250,10 @@ static int ufshcd_clock_scaling_prepare(struct ufs_hba *hba)
 	return ret;
 }
 
-static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba, bool writelock)
+static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba)
 {
-	if (writelock)
-		up_write(&hba->clk_scaling_lock);
-	else
-		up_read(&hba->clk_scaling_lock);
+	up_write(&hba->clk_scaling_lock);
+
 	ufshcd_scsi_unblock_requests(hba);
 	ufshcd_release(hba);
 }
@@ -1271,7 +1270,7 @@ static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba, bool writelock)
 static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up)
 {
 	int ret = 0;
-	bool is_writelock = true;
+	bool wb_toggle = false;
 
 	ret = ufshcd_clock_scaling_prepare(hba);
 	if (ret)
@@ -1300,13 +1299,19 @@ static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up)
 		}
 	}
 
-	/* Enable Write Booster if we have scaled up else disable it */
-	downgrade_write(&hba->clk_scaling_lock);
-	is_writelock = false;
-	ufshcd_wb_toggle(hba, scale_up);
+	/* Disable clk_scaling until ufshcd_wb_toggle finish */
+	hba->clk_scaling.is_allowed = false;
+	wb_toggle = true;
 
 out_unprepare:
-	ufshcd_clock_scaling_unprepare(hba, is_writelock);
+	ufshcd_clock_scaling_unprepare(hba);
+
+	/* Enable Write Booster if we have scaled up else disable it */
+	if (wb_toggle) {
+		ufshcd_wb_toggle(hba, scale_up);
+		ufshcd_clk_scaling_allow(hba, true);
+	}
+
 	return ret;
 }
 
-- 
2.18.0