mtd: spi-nor: fsl-quadspi: i.MX6SX: fixed the random QSPI access failed issue

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.

The root cause is that the divider is not glitchless in i.MX6SX chip.
If qspi clock enabled then change clock frequency by call clk_set_rate,
there will be glitch at low possiblity rate and pass to qspi controller.
The controler will be hang by this glitch.

Based on the new clock flag(CLK_SET_RATE_GATE) and new framework, we
need to change the approach of seting clock rate.
1. Disable clock.
2. call clk_set_rate.
3. Enable clock again.

Signed-off-by: Han Xu <han.xu@freescale.com>
Signed-off-by: Frank Li <Frank.Li@freescale.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/spi-nor/fsl-quadspi.c

@@ -655,6 +655,32 @@ 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)
 {
@@ -662,11 +688,18 @@ 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 to avoid glitch pass to controller */
+	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;
 
+	ret = fsl_qspi_clk_prep_enable(q);
+	if (ret)
+		return ret;
+
 	/* Init the LUT table. */
 	fsl_qspi_init_lut(q);
 
@@ -698,10 +731,17 @@ static int fsl_qspi_nor_setup_last(struct fsl_qspi *q)
 	if (needs_4x_clock(q))
 		rate *= 4;
 
+	/* disable and unprepare clock to avoid glitch pass to controller */
+	fsl_qspi_clk_disable_unprep(q);
+
 	ret = clk_set_rate(q->clk, rate);
 	if (ret)
 		return ret;
 
+	ret = fsl_qspi_clk_prep_enable(q);
+	if (ret)
+		return ret;
+
 	/* Init the LUT table again. */
 	fsl_qspi_init_lut(q);
 
@@ -844,22 +884,16 @@ 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;
 }
 
@@ -867,8 +901,7 @@ 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);
 }
 
@@ -918,15 +951,9 @@ 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;
 	}
 
@@ -1032,8 +1059,7 @@ 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:
@@ -1046,9 +1072,9 @@ 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;
 }
 
@@ -1069,8 +1095,6 @@ 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);
@@ -1085,12 +1109,19 @@ 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;
 }