spi: imx: mx51-ecspi: Reinstate low-speed CONFIGREG delay

Since 00b80ac9 ("spi: imx: mx51-ecspi: Move some initialisation to
prepare_message hook."), the MX51_ECSPI_CONFIG write no longer happens
in prepare_transfer hook, but rather in prepare_message hook, however
the MX51_ECSPI_CONFIG delay is still left in prepare_transfer hook and
thus has no effect. This leads to low bus frequency operation problems
described in 6fd8b850 ("spi: spi-imx: Fix out-of-order CS/SCLK
operation at low speeds") again.

Move the MX51_ECSPI_CONFIG write delay into the prepare_message hook
as well, thus reinstating the low bus frequency fix.

Fixes: 00b80ac9 ("spi: imx: mx51-ecspi: Move some initialisation to prepare_message hook.")
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Cc: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20210703022300.296114-1-marex@denx.deSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-imx.c

@@ -506,7 +506,7 @@ static int mx51_ecspi_prepare_message(struct spi_imx_data *spi_imx,
 {
 	struct spi_device *spi = msg->spi;
 	u32 ctrl = MX51_ECSPI_CTRL_ENABLE;
-	u32 testreg;
+	u32 testreg, delay;
 	u32 cfg = readl(spi_imx->base + MX51_ECSPI_CONFIG);
 
 	/* set Master or Slave mode */
@@ -567,6 +567,23 @@ static int mx51_ecspi_prepare_message(struct spi_imx_data *spi_imx,
 
 	writel(cfg, spi_imx->base + MX51_ECSPI_CONFIG);
 
+	/*
+	 * Wait until the changes in the configuration register CONFIGREG
+	 * propagate into the hardware. It takes exactly one tick of the
+	 * SCLK clock, but we will wait two SCLK clock just to be sure. The
+	 * effect of the delay it takes for the hardware to apply changes
+	 * is noticable if the SCLK clock run very slow. In such a case, if
+	 * the polarity of SCLK should be inverted, the GPIO ChipSelect might
+	 * be asserted before the SCLK polarity changes, which would disrupt
+	 * the SPI communication as the device on the other end would consider
+	 * the change of SCLK polarity as a clock tick already.
+	 */
+	delay = (2 * 1000000) / spi_imx->spi_bus_clk;
+	if (likely(delay < 10))	/* SCLK is faster than 100 kHz */
+		udelay(delay);
+	else			/* SCLK is _very_ slow */
+		usleep_range(delay, delay + 10);
+
 	return 0;
 }
 
@@ -574,7 +591,7 @@ static int mx51_ecspi_prepare_transfer(struct spi_imx_data *spi_imx,
 				       struct spi_device *spi)
 {
 	u32 ctrl = readl(spi_imx->base + MX51_ECSPI_CTRL);
-	u32 clk, delay;
+	u32 clk;
 
 	/* Clear BL field and set the right value */
 	ctrl &= ~MX51_ECSPI_CTRL_BL_MASK;
@@ -596,23 +613,6 @@ static int mx51_ecspi_prepare_transfer(struct spi_imx_data *spi_imx,
 
 	writel(ctrl, spi_imx->base + MX51_ECSPI_CTRL);
 
-	/*
-	 * Wait until the changes in the configuration register CONFIGREG
-	 * propagate into the hardware. It takes exactly one tick of the
-	 * SCLK clock, but we will wait two SCLK clock just to be sure. The
-	 * effect of the delay it takes for the hardware to apply changes
-	 * is noticable if the SCLK clock run very slow. In such a case, if
-	 * the polarity of SCLK should be inverted, the GPIO ChipSelect might
-	 * be asserted before the SCLK polarity changes, which would disrupt
-	 * the SPI communication as the device on the other end would consider
-	 * the change of SCLK polarity as a clock tick already.
-	 */
-	delay = (2 * 1000000) / clk;
-	if (likely(delay < 10))	/* SCLK is faster than 100 kHz */
-		udelay(delay);
-	else			/* SCLK is _very_ slow */
-		usleep_range(delay, delay + 10);
-
 	return 0;
 }