[PATCH v7 5/6] drm: renesas: rz-du: mipi_dsi: Add support for LPCLK clock handling

[Prabhakar]

From: Lad Prabhakar <prabhakar.mahadev-lad.rj at bp.renesas.com>

Add LPCLK clock support in the RZ/G2L MIPI DSI driver via the optional
clock API. This clock is required by some SoCs like RZ/V2H(P) for proper
DPHY configuration, whereas it is absent on others like RZ/G2L.

Introduce a new `lpclk` field in the `rzg2l_mipi_dsi` structure and
conditionally acquire the "lpclk" clock using `devm_clk_get_optional()`
during probe. This allows LPCLK-aware SoCs to pass the clock via device
tree without impacting existing platforms.

Co-developed-by: Fabrizio Castro <fabrizio.castro.jz at renesas.com>
Signed-off-by: Fabrizio Castro <fabrizio.castro.jz at renesas.com>
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj at bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz at bp.renesas.com>
---
v6->v7:
- New patch
Note, this patch was previously part of series [0].
[0] https://lore.kernel.org/all/20250609225630.502888-1-prabhakar.mahadev-lad.rj@bp.renesas.com/
---
 drivers/gpu/drm/renesas/rz-du/rzg2l_mipi_dsi.c | 5 +++++
 1 file changed, 5 insertions(+)

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 f87337c3cbb5..893a90c7a886 100644
--- a/drivers/gpu/drm/renesas/rz-du/rzg2l_mipi_dsi.c
+++ b/drivers/gpu/drm/renesas/rz-du/rzg2l_mipi_dsi.c
@@ -68,6 +68,7 @@ struct rzg2l_mipi_dsi {
 	struct drm_bridge *next_bridge;
 
 	struct clk *vclk;
+	struct clk *lpclk;
 
 	enum mipi_dsi_pixel_format format;
 	unsigned int num_data_lanes;
@@ -979,6 +980,10 @@ static int rzg2l_mipi_dsi_probe(struct platform_device *pdev)
 	if (IS_ERR(dsi->vclk))
 		return PTR_ERR(dsi->vclk);
 
+	dsi->lpclk = devm_clk_get_optional(dsi->dev, "lpclk");
+	if (IS_ERR(dsi->lpclk))
+		return PTR_ERR(dsi->lpclk);
+
 	dsi->rstc = devm_reset_control_get_optional_exclusive(dsi->dev, "rst");
 	if (IS_ERR(dsi->rstc))
 		return dev_err_probe(dsi->dev, PTR_ERR(dsi->rstc),
-- 
2.50.1