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

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

Tested-by: Adam Ford <aford173@gmail.com> #imx8mp-beacon
Reviewed-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Tested-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Signed-off-by: Dominique Martinet <dominique.martinet@atmark-techno.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20240907-hdmi-tolerance-v2-1-b9d7abd89f5c@codewreck.org
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240907-hdmi-tolerance-v2-1-b9d7abd89f5c@codewreck.org

diff --git a/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx.c b/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx.c
index 4a3a8a3ce250ea31631becccda0ae8257c3c0643..8fcc6d18f4ab9b05b8482f9576ade5f7a93dde56 100644 (file)
--- 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 +31,14 @@ 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);
+       /* imx8mp's pixel clock generator (fsl-samsung-hdmi) cannot generate
+        * all possible frequencies, so allow some tolerance to support more
+        * modes.
+        * Allow 0.5% difference allowed in various standards (VESA, CEA861)
+        * 0.5% = 5/1000 tolerance (mode->clock is 1/1000)
+        */
+       if (abs(round_rate - mode->clock * 1000) > mode->clock * 5)
                return MODE_CLOCK_RANGE;
 
        /* We don't support double-clocked and Interlaced modes */