drm/rockchip: dw_hdmi: Adjust cklvl & txlvl for RF/EMI

Dut to the high HDMI signal voltage driver, Mickey have meet
a serious RF/EMI problem, so we decided to reduce HDMI signal
voltage to a proper value.

The default params for phy is cklvl = 20 & txlvl = 13 (RF/EMI failed)
  ck: lvl = 13, term=100, vlo = 2.71, vhi=3.14, vswing = 0.43
  tx: lvl = 20, term=100, vlo = 2.81, vhi=3.16, vswing = 0.35

1. We decided to reduce voltage value to lower, but VSwing still
keep high, RF/EMI have been improved but still failed.
   ck: lvl =  6, term=100, vlo = 2.61, vhi=3.11, vswing = 0.50
   tx: lvl =  6, term=100, vlo = 2.61, vhi=3.11, vswing = 0.50

2. We try to keep voltage value and vswing both lower, then RF/EMI
test all passed  ;)
   ck: lvl = 11, term= 66, vlo = 2.68, vhi=3.09, vswing = 0.40
   tx: lvl = 11, term= 66, vlo = 2.68, vhi=3.09, vswing = 0.40
When we back to run HDMI different test and single-end test, we see
different test passed, but signle-end test failed. The oscilloscope
show that simgle-end clock's VL value is 1.78v (which remind LowLimit
should not lower then 2.6v).

3. That's to say there are some different between PHY document and
measure value. And according to experiment 2 results, we need to
higher clock voltage and lower data voltage, then we can keep RF/EMI
satisfied and single-end & differen test passed.
  ck: lvl =  9, term=100, vlo = 2.65, vhi=3.12, vswing = 0.47
  tx: lvl = 16, term=100, vlo = 2.75, vhi=3.15, vswing = 0.39

Signed-off-by: Yakir Yang <ykk@rock-chips.com>
Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20240908145511.3331451-3-jonas@kwiboo.se

diff --git a/drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c b/drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c
index 36cc700766fd82cd0d18dd32a2f21d507f0f388d..fc5e87285a919a6a24a6602d0037ee96815dce74 100644 (file)
--- a/drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c
+++ b/drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c
@@ -202,7 +202,7 @@ static const struct dw_hdmi_curr_ctrl rockchip_cur_ctr[] = {
 static const struct dw_hdmi_phy_config rockchip_phy_config[] = {
        /*pixelclk   symbol   term   vlev*/
        { 74250000,  0x8009, 0x0004, 0x0272},
-       { 148500000, 0x802b, 0x0004, 0x028d},
+       { 165000000, 0x802b, 0x0004, 0x0209},
        { 297000000, 0x8039, 0x0005, 0x028d},
        { ~0UL,      0x0000, 0x0000, 0x0000}
 };