[PATCH v3 3/3] drm: renesas: rzg2l_mipi_dsi: Fix deassert/assert 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().

The CMN_RSTB signal is not required for reading PHY registers in the
probe. Move reset_control_assert() from rzg2l_mipi_dsi_dphy_exit() to
rzg2l_mipi_dsi_stop(), placing it before the dphy_exit() call. Since this
reset signal is optional for RZ/V2H, the call is a no-op on that SoC.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
---
v2->v3:
 * Merged patch#2 and patch#3 to avoid breakage.
 * Updated commit description
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 | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 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 9d9f77d8f949..715872130780 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;
-
-	fsleep(1000);
-
 	return 0;
 }
 
@@ -541,8 +534,6 @@ static void rzg2l_mipi_dsi_dphy_exit(struct rzg2l_mipi_dsi *dsi)
 
 	dphyctrl0 &= ~(DSIDPHYCTRL0_EN_LDO1200 | DSIDPHYCTRL0_EN_BGR);
 	rzg2l_mipi_dsi_phy_write(dsi, DSIDPHYCTRL0, dphyctrl0);
-
-	reset_control_assert(dsi->rstc);
 }
 
 static int rzg2l_dphy_conf_clks(struct rzg2l_mipi_dsi *dsi, unsigned long mode_freq,
@@ -811,6 +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;
+
+		fsleep(1000);
+	}
+
 	return 0;
 
 err_phy:
@@ -822,6 +821,7 @@ static int rzg2l_mipi_dsi_startup(struct rzg2l_mipi_dsi *dsi,
 
 static void rzg2l_mipi_dsi_stop(struct rzg2l_mipi_dsi *dsi)
 {
+	reset_control_assert(dsi->rstc);
 	dsi->info->dphy_exit(dsi);
 	pm_runtime_put(dsi->dev);
 }
-- 
2.43.0