[PATCH v2 3/4] drm: renesas: rzg2l_mipi_dsi: Fix deassert of CMN_RSTB signal

[Biju <biju.das.au@gmail.com>]

From: Biju Das <biju.das.jz@bp.renesas.com>

The RZ/G2L hardware manual (Rev. 1.50, May 2025), Section 34.4.2.1,
requires deasserting the CMN_RSTB signal after setting the Link
registers. Move the reset_control_deassert() call from
rzg2l_mipi_dsi_dphy_init() to rzg2l_mipi_dsi_startup(), placing it
after the Link register writes. This reset signal is optional for
RZ/V2H SoCs, so add a NULL check. Drop the unused ret variable from
rzg2l_mipi_dsi_dphy_init().

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
---
v1->v2:
 * Updated commit header and description
 * Moved the code from rzg2l_mipi_dsi_dphy_init() to rzg2l_mipi_dsi_startup()
 * Moved the check before calling reset_control_deassert(), so that it will be
   skipped for RZ/V2H SoC
---
 drivers/gpu/drm/renesas/rz-du/rzg2l_mipi_dsi.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/renesas/rz-du/rzg2l_mipi_dsi.c b/drivers/gpu/drm/renesas/rz-du/rzg2l_mipi_dsi.c
index d2da247abf05..5020be0f72ac 100644
--- a/drivers/gpu/drm/renesas/rz-du/rzg2l_mipi_dsi.c
+++ b/drivers/gpu/drm/renesas/rz-du/rzg2l_mipi_dsi.c
@@ -484,7 +484,6 @@ static int rzg2l_mipi_dsi_dphy_init(struct rzg2l_mipi_dsi *dsi,
 	u32 dphytim1;
 	u32 dphytim2;
 	u32 dphytim3;
-	int ret;
 
 	/* All DSI global operation timings are set with recommended setting */
 	for (i = 0; i < ARRAY_SIZE(rzg2l_mipi_dsi_global_timings); ++i) {
@@ -524,12 +523,6 @@ static int rzg2l_mipi_dsi_dphy_init(struct rzg2l_mipi_dsi *dsi,
 	rzg2l_mipi_dsi_phy_write(dsi, DSIDPHYTIM2, dphytim2);
 	rzg2l_mipi_dsi_phy_write(dsi, DSIDPHYTIM3, dphytim3);
 
-	ret = reset_control_deassert(dsi->rstc);
-	if (ret < 0)
-		return ret;
-
-	udelay(1);
-
 	return 0;
 }
 
@@ -809,6 +802,14 @@ static int rzg2l_mipi_dsi_startup(struct rzg2l_mipi_dsi *dsi,
 	FIELD_MODIFY(DSISETR_MRPSZ, &dsisetr, RZG2L_DCS_BUF_SIZE);
 	rzg2l_mipi_dsi_link_write(dsi, DSISETR, dsisetr);
 
+	if (dsi->rstc) {
+		ret = reset_control_deassert(dsi->rstc);
+		if (ret < 0)
+			goto err_phy;
+
+		udelay(1);
+	}
+
 	return 0;
 
 err_phy:
-- 
2.43.0