[PATCH v7 4/7] drm/bridge: fsl-ldb: Use clk_round_rate() to validate "ldb" clock rate

[Liu Ying]

Multiple display modes could be read from a display device's EDID.
Use clk_round_rate() to validate the "ldb" clock rate for each mode
in drm_bridge_funcs::mode_valid() to filter unsupported modes out.

Signed-off-by: Liu Ying <victor.liu at nxp.com>
---
Note that this patch depends on a patch in shawnguo/imx/fixes:
https://patchwork.kernel.org/project/linux-arm-kernel/patch/20241017031146.157996-1-marex@denx.de/

v7:
* No change.

v6:
* Drop pixel clock rate validation.

v5:
* No change.

v4:
* No change.

v3:
* No change.

v2:
* Add more comments in fsl-ldb.c and commit message about pixel clock
  rate validation.  (Maxime)

 drivers/gpu/drm/bridge/fsl-ldb.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/bridge/fsl-ldb.c b/drivers/gpu/drm/bridge/fsl-ldb.c
index b559f3e0bef6..d9436ff9ccc3 100644
--- a/drivers/gpu/drm/bridge/fsl-ldb.c
+++ b/drivers/gpu/drm/bridge/fsl-ldb.c
@@ -270,10 +270,16 @@ fsl_ldb_mode_valid(struct drm_bridge *bridge,
 		   const struct drm_display_mode *mode)
 {
 	struct fsl_ldb *fsl_ldb = to_fsl_ldb(bridge);
+	unsigned long link_freq;
 
 	if (mode->clock > (fsl_ldb_is_dual(fsl_ldb) ? 160000 : 80000))
 		return MODE_CLOCK_HIGH;
 
+	/* Validate "ldb" clock rate. */
+	link_freq = fsl_ldb_link_frequency(fsl_ldb, mode->clock);
+	if (link_freq != clk_round_rate(fsl_ldb->clk, link_freq))
+		return MODE_NOCLOCK;
+
 	return MODE_OK;
 }
 
-- 
2.34.1