[PATCH 4/7] mtd: spi-nor: fsl-quadspi: i.MX6SX: fixed the random QSPI access failed issue

[Frank.Li at freescale.com]

From: Allen Xu <b45815 at freescale.com>

We found there is a low probability(5%) QSPI access timeout issue,
usually it happened on kernel boot stage, the first time kernel tried to
access QSPI chip. The READ_ID command was sent but not executed,
consequently the probe function failed.

Finally we located the issue by these steps.

1. Since the issue happened randomly and usually it cost half day to
reproduce, we add more debug code in driver, to create a timeout file if
the issue occurred.

2. Prepared an autorun script to keep rebooting the system and check if
the timeout file existed, if the file existed, stop reboot.

3. The system will stop rebooting when timeout error occurred, set the
CCM_CCOSR register and related IOMUX to measure QPSI clock, found there
is no clock output, while clock output can be measured when QSPI driver
successfully probed.

4. Check the code and found QSPI clock rate was changed while not
disabled clock gate, most of the multiplexers on i.MX6 are glitch ones,
clock glitch may occurred and propagated into downstream clock dividers

Based on the new clock flag(CLK_SET_RATE_GATE) and new framework, we
need to change the approach of seting clock rate. In current
implementation, there are several places in which the clock was touched.

1. probe function. prepare and enable clock before setting the QSPI
register, disable and unprepare the clock before exit.

2. nor_setup & nor_setup_last, since we change clock rate in these two
functions.

3. fsl_qspi_prep and fsl_qspi_unprep, clock was enabled only when got
QSPI access request.

4. resume function. Clock was required to restroe the setting after
resume, disable the clock before exit.

Signed-off-by: Allen Xu <b45815 at freescale.com>
Signed-off-by: Frank Li <Frank.Li at freescale.com>
---
 drivers/mtd/spi-nor/fsl-quadspi.c | 83 +++++++++++++++++++++++++++------------
 1 file changed, 58 insertions(+), 25 deletions(-)

diff --git a/drivers/mtd/spi-nor/fsl-quadspi.c b/drivers/mtd/spi-nor/fsl-quadspi.c
index 921fba1..1419f1f 100644
--- a/drivers/mtd/spi-nor/fsl-quadspi.c
+++ b/drivers/mtd/spi-nor/fsl-quadspi.c
@@ -653,6 +653,32 @@ static void fsl_qspi_init_abh_read(struct fsl_qspi *q)
 		q->iobase + QUADSPI_BFGENCR);
 }
 
+/* This function was used to prepare and enable QSPI clock */
+static int fsl_qspi_clk_prep_enable(struct fsl_qspi *q)
+{
+	int ret;
+
+	ret = clk_prepare_enable(q->clk_en);
+	if (ret)
+		return ret;
+
+	ret = clk_prepare_enable(q->clk);
+	if (ret) {
+		clk_disable_unprepare(q->clk_en);
+		return ret;
+	}
+
+	return 0;
+}
+
+/* This function was used to disable and unprepare QSPI clock */
+static void fsl_qspi_clk_disable_unprep(struct fsl_qspi *q)
+{
+	clk_disable_unprepare(q->clk);
+	clk_disable_unprepare(q->clk_en);
+
+}
+
 /* We use this function to do some basic init for spi_nor_scan(). */
 static int fsl_qspi_nor_setup(struct fsl_qspi *q)
 {
@@ -660,11 +686,19 @@ static int fsl_qspi_nor_setup(struct fsl_qspi *q)
 	u32 reg;
 	int ret;
 
-	/* the default frequency, we will change it in the future.*/
+	/* disable and unprepare clock first */
+	fsl_qspi_clk_disable_unprep(q);
+
+	/* the default frequency, we will change it in the future. */
 	ret = clk_set_rate(q->clk, 66000000);
 	if (ret)
 		return ret;
 
+	/* prepare and enable the clock */
+	ret = fsl_qspi_clk_prep_enable(q);
+	if (ret)
+		return ret;
+
 	/* Init the LUT table. */
 	fsl_qspi_init_lut(q);
 
@@ -696,10 +730,18 @@ static int fsl_qspi_nor_setup_last(struct fsl_qspi *q)
 	if (needs_4x_clock(q))
 		rate *= 4;
 
+	/* disable and unprepare clock first */
+	fsl_qspi_clk_disable_unprep(q);
+
 	ret = clk_set_rate(q->clk, rate);
 	if (ret)
 		return ret;
 
+	/* prepare and enable the clock */
+	ret = fsl_qspi_clk_prep_enable(q);
+	if (ret)
+		return ret;
+
 	/* Init the LUT table again. */
 	fsl_qspi_init_lut(q);
 
@@ -841,22 +883,16 @@ static int fsl_qspi_prep(struct spi_nor *nor, enum spi_nor_ops ops)
 	int ret;
 
 	mutex_lock(&q->lock);
-	ret = clk_enable(q->clk_en);
-	if (ret)
-		goto err_mutex;
 
-	ret = clk_enable(q->clk);
+	ret = fsl_qspi_clk_prep_enable(q);
 	if (ret)
-		goto err_clk;
+		goto err_mutex;
 
 	fsl_qspi_set_base_addr(q, nor);
 	return 0;
 
-err_clk:
-	clk_disable(q->clk_en);
 err_mutex:
 	mutex_unlock(&q->lock);
-
 	return ret;
 }
 
@@ -864,8 +900,7 @@ static void fsl_qspi_unprep(struct spi_nor *nor, enum spi_nor_ops ops)
 {
 	struct fsl_qspi *q = nor->priv;
 
-	clk_disable(q->clk);
-	clk_disable(q->clk_en);
+	fsl_qspi_clk_disable_unprep(q);
 	mutex_unlock(&q->lock);
 }
 
@@ -909,15 +944,9 @@ static int fsl_qspi_probe(struct platform_device *pdev)
 	if (IS_ERR(q->clk))
 		return PTR_ERR(q->clk);
 
-	ret = clk_prepare_enable(q->clk_en);
+	ret = fsl_qspi_clk_prep_enable(q);
 	if (ret) {
-		dev_err(dev, "cannot enable the qspi_en clock: %d\n", ret);
-		return ret;
-	}
-
-	ret = clk_prepare_enable(q->clk);
-	if (ret) {
-		dev_err(dev, "cannot enable the qspi clock: %d\n", ret);
+		dev_err(dev, "can not enable the clock\n");
 		goto clk_failed;
 	}
 
@@ -1023,8 +1052,7 @@ static int fsl_qspi_probe(struct platform_device *pdev)
 	if (ret)
 		goto last_init_failed;
 
-	clk_disable(q->clk);
-	clk_disable(q->clk_en);
+	fsl_qspi_clk_disable_unprep(q);
 	return 0;
 
 last_init_failed:
@@ -1037,9 +1065,9 @@ last_init_failed:
 mutex_failed:
 	mutex_destroy(&q->lock);
 irq_failed:
-	clk_disable_unprepare(q->clk);
+	fsl_qspi_clk_disable_unprep(q);
 clk_failed:
-	clk_disable_unprepare(q->clk_en);
+	dev_err(dev, "Freescale QuadSPI probe failed\n");
 	return ret;
 }
 
@@ -1060,8 +1088,6 @@ static int fsl_qspi_remove(struct platform_device *pdev)
 	writel(0x0, q->iobase + QUADSPI_RSER);
 
 	mutex_destroy(&q->lock);
-	clk_unprepare(q->clk);
-	clk_unprepare(q->clk_en);
 
 	if (q->ahb_addr)
 		iounmap(q->ahb_addr);
@@ -1076,12 +1102,19 @@ static int fsl_qspi_suspend(struct platform_device *pdev, pm_message_t state)
 
 static int fsl_qspi_resume(struct platform_device *pdev)
 {
+	int ret;
 	struct fsl_qspi *q = platform_get_drvdata(pdev);
 
+	ret = fsl_qspi_clk_prep_enable(q);
+	if (ret)
+		return ret;
+
 	fsl_qspi_nor_setup(q);
 	fsl_qspi_set_map_addr(q);
 	fsl_qspi_nor_setup_last(q);
 
+	fsl_qspi_clk_disable_unprep(q);
+
 	return 0;
 }
 
-- 
1.9.1