[PATCH] drm/bridge: imx8mp-hdmi-tx: allow 0.5% margin with selected clock

[Dominique Martinet <dominique.martinet@atmark-techno.com>]

This allows the hdmi driver to pick e.g. 64.8MHz instead of 65Mhz when we
cannot output the exact frequency, enabling the imx8mp HDMI output to
support more modes

Signed-off-by: Dominique Martinet <dominique.martinet@atmark-techno.com>
---
This completes the patch series sent by Adam Ford here:
https://lkml.kernel.org/r/20240904023310.163371-1-aford173@gmail.com

and makes the cheap screens we recommend work with our imx8mp board
without further kludging.


 drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx.c b/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx.c
index 13bc570c5473..9431cd5e06c3 100644
--- a/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx.c
+++ b/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx.c
@@ -23,6 +23,7 @@ imx8mp_hdmi_mode_valid(struct dw_hdmi *dw_hdmi, void *data,
 		       const struct drm_display_mode *mode)
 {
 	struct imx8mp_hdmi *hdmi = (struct imx8mp_hdmi *)data;
+	long round_rate;
 
 	if (mode->clock < 13500)
 		return MODE_CLOCK_LOW;
@@ -30,8 +31,9 @@ imx8mp_hdmi_mode_valid(struct dw_hdmi *dw_hdmi, void *data,
 	if (mode->clock > 297000)
 		return MODE_CLOCK_HIGH;
 
-	if (clk_round_rate(hdmi->pixclk, mode->clock * 1000) !=
-	    mode->clock * 1000)
+	round_rate = clk_round_rate(hdmi->pixclk, mode->clock * 1000);
+	/* accept 0.5% = 1/200 = 5/1000 tolerance */
+	if (abs(round_rate - mode->clock * 1000) > mode->clock * 5)
 		return MODE_CLOCK_RANGE;
 
 	/* We don't support double-clocked and Interlaced modes */
-- 
2.39.2