spi: spi-rspi: Add support to deassert/assert reset line

On RZ/G2L SoC we need to explicitly deassert the reset line
for the device to work, use this opportunity to deassert/assert
reset line in spi-rspi driver.

This patch adds support to read the "resets" property (if available)
from DT and perform deassert/assert when required.
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20211118031041.2312-3-prabhakar.mahadev-lad.rj@bp.renesas.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-rspi.c

@@ -21,6 +21,7 @@
 #include <linux/dma-mapping.h>
 #include <linux/of_device.h>
 #include <linux/pm_runtime.h>
+#include <linux/reset.h>
 #include <linux/sh_dma.h>
 #include <linux/spi/spi.h>
 #include <linux/spi/rspi.h>
@@ -1225,8 +1226,14 @@ static const struct of_device_id rspi_of_match[] = {
 
 MODULE_DEVICE_TABLE(of, rspi_of_match);
 
+static void rspi_reset_control_assert(void *data)
+{
+	reset_control_assert(data);
+}
+
 static int rspi_parse_dt(struct device *dev, struct spi_controller *ctlr)
 {
+	struct reset_control *rstc;
 	u32 num_cs;
 	int error;
 
@@ -1238,6 +1245,24 @@ static int rspi_parse_dt(struct device *dev, struct spi_controller *ctlr)
 	}
 
 	ctlr->num_chipselect = num_cs;
+
+	rstc = devm_reset_control_get_optional_exclusive(dev, NULL);
+	if (IS_ERR(rstc))
+		return dev_err_probe(dev, PTR_ERR(rstc),
+					     "failed to get reset ctrl\n");
+
+	error = reset_control_deassert(rstc);
+	if (error) {
+		dev_err(dev, "failed to deassert reset %d\n", error);
+		return error;
+	}
+
+	error = devm_add_action_or_reset(dev, rspi_reset_control_assert, rstc);
+	if (error) {
+		dev_err(dev, "failed to register assert devm action, %d\n", error);
+		return error;
+	}
+
 	return 0;
 }
 #else