From 926a299c42e38bbe8bb909eae0146e676b66afe4 Mon Sep 17 00:00:00 2001
From: Russell King <rmk+kernel@armlinux.org.uk>
Date: Thu, 2 Aug 2018 10:27:15 +0100
Subject: [PATCH] drm/i2c: tda998x: correct PLL divider calculation
The serializer PLL divider is a power-of-two divider, so our calculation
which assumes that it's a numerical divider is incorrect. Replace it
with one that results in a power-of-two divider value instead.
Tested with all supported modes with a Samsung S24C750.
Tested-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
---
drivers/gpu/drm/i2c/tda998x_drv.c | 20 ++++++++++++++------
1 file changed, 14 insertions(+), 6 deletions(-)
diff --git a/drivers/gpu/drm/i2c/tda998x_drv.c b/drivers/gpu/drm/i2c/tda998x_drv.c
index 7313ff835f351..0df86e9281913 100644
--- a/drivers/gpu/drm/i2c/tda998x_drv.c
+++ b/drivers/gpu/drm/i2c/tda998x_drv.c
@@ -1343,6 +1343,7 @@ static void tda998x_bridge_mode_set(struct drm_bridge *bridge,
struct drm_display_mode *adjusted_mode)
{
struct tda998x_priv *priv = bridge_to_tda998x_priv(bridge);
+ unsigned long tmds_clock;
u16 ref_pix, ref_line, n_pix, n_line;
u16 hs_pix_s, hs_pix_e;
u16 vs1_pix_s, vs1_pix_e, vs1_line_s, vs1_line_e;
@@ -1413,12 +1414,19 @@ static void tda998x_bridge_mode_set(struct drm_bridge *bridge,
(mode->vsync_end - mode->vsync_start)/2;
}
- div = 148500 / mode->clock;
- if (div != 0) {
- div--;
- if (div > 3)
- div = 3;
- }
+ tmds_clock = mode->clock;
+
+ /*
+ * The divisor is power-of-2. The TDA9983B datasheet gives
+ * this as ranges of Msample/s, which is 10x the TMDS clock:
+ * 0 - 800 to 1500 Msample/s
+ * 1 - 400 to 800 Msample/s
+ * 2 - 200 to 400 Msample/s
+ * 3 - as 2 above
+ */
+ for (div = 0; div < 3; div++)
+ if (80000 >> div <= tmds_clock)
+ break;
mutex_lock(&priv->audio_mutex);
--
2.30.2