linux-kernel - [PATCH v1 2/6] drm/rockchip: dw_hdmi: adjust cklvl & txlvl for RF/EMI

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Date:	Mon, 11 Jul 2016 19:05:39 +0800
From:	Yakir Yang <ykk@...k-chips.com>
To:	Mark Yao <mark.yao@...k-chips.com>,
	Heiko Stuebner <heiko@...ech.de>,
	Rob Herring <robh+dt@...nel.org>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Andy Yan <andy.yan@...k-chips.com>
Cc:	David Airlie <airlied@...ux.ie>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Kumar Gala <galak@...eaurora.org>,
	Zheng Yang <zhengyang@...k-chips.com>, xhc@...k-chips.com,
	dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-rockchip@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org,
	Yakir Yang <ykk@...k-chips.com>
Subject: [PATCH v1 2/6] 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@...k-chips.com>
Reviewed-by: Douglas Anderson <dianders@...omium.org>
---
 drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c b/drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c
index a621118..cdb63ac 100644
--- a/drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c
+++ b/drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c
@@ -124,7 +124,7 @@ 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}
 };
-- 
1.9.1