spi: fsl-espi: add (un)prepare_transfer_hardware calls to save power if SPI is not in use

Use (un)prepare_transfer_hardware calls to set fsl-espi to
low-power idle if not in use. Reference manual states:

"The eSPI is in a idle state and consumes minimal power.
The eSPI BRG is not functioning and the input clock is disabled"
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-fsl-espi.c

@@ -588,6 +588,38 @@ static void fsl_espi_remove(struct mpc8xxx_spi *mspi)
 	iounmap(mspi->reg_base);
 }
 
+static int fsl_espi_suspend(struct spi_master *master)
+{
+	struct mpc8xxx_spi *mpc8xxx_spi;
+	struct fsl_espi_reg *reg_base;
+	u32 regval;
+
+	mpc8xxx_spi = spi_master_get_devdata(master);
+	reg_base = mpc8xxx_spi->reg_base;
+
+	regval = mpc8xxx_spi_read_reg(&reg_base->mode);
+	regval &= ~SPMODE_ENABLE;
+	mpc8xxx_spi_write_reg(&reg_base->mode, regval);
+
+	return 0;
+}
+
+static int fsl_espi_resume(struct spi_master *master)
+{
+	struct mpc8xxx_spi *mpc8xxx_spi;
+	struct fsl_espi_reg *reg_base;
+	u32 regval;
+
+	mpc8xxx_spi = spi_master_get_devdata(master);
+	reg_base = mpc8xxx_spi->reg_base;
+
+	regval = mpc8xxx_spi_read_reg(&reg_base->mode);
+	regval |= SPMODE_ENABLE;
+	mpc8xxx_spi_write_reg(&reg_base->mode, regval);
+
+	return 0;
+}
+
 static struct spi_master * fsl_espi_probe(struct device *dev,
 		struct resource *mem, unsigned int irq)
 {
@@ -614,6 +646,8 @@ static struct spi_master * fsl_espi_probe(struct device *dev,
 	master->setup = fsl_espi_setup;
 	master->cleanup = fsl_espi_cleanup;
 	master->transfer_one_message = fsl_espi_do_one_msg;
+	master->prepare_transfer_hardware = fsl_espi_resume;
+	master->unprepare_transfer_hardware = fsl_espi_suspend;
 
 	mpc8xxx_spi = spi_master_get_devdata(master);
 	mpc8xxx_spi->spi_remove = fsl_espi_remove;
@@ -761,25 +795,15 @@ static int of_fsl_espi_remove(struct platform_device *dev)
 static int of_fsl_espi_suspend(struct device *dev)
 {
 	struct spi_master *master = dev_get_drvdata(dev);
-	struct mpc8xxx_spi *mpc8xxx_spi;
-	struct fsl_espi_reg *reg_base;
-	u32 regval;
 	int ret;
 
-	mpc8xxx_spi = spi_master_get_devdata(master);
-	reg_base = mpc8xxx_spi->reg_base;
-
 	ret = spi_master_suspend(master);
 	if (ret) {
 		dev_warn(dev, "cannot suspend master\n");
 		return ret;
 	}
 
-	regval = mpc8xxx_spi_read_reg(&reg_base->mode);
-	regval &= ~SPMODE_ENABLE;
-	mpc8xxx_spi_write_reg(&reg_base->mode, regval);
-
-	return 0;
+	return fsl_espi_suspend(master);
 }
 
 static int of_fsl_espi_resume(struct device *dev)