linux-kernel - Re: [PATCH] clk: rockchip: change PLL setting for better clock jitter

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Date:	Wed, 29 Oct 2014 20:51:50 +0100
From:	Heiko Stübner <heiko@...ech.de>
To:	Kever Yang <kever.yang@...k-chips.com>
Cc:	Mike Turquette <mturquette@...aro.org>, dianders@...omium.org,
	sonnyrao@...omium.org, addy.ke@...k-chips.com, cf@...k-chips.com,
	xjq@...k-chips.com, hj@...k-chips.com, huangtao@...k-chips.com,
	dkl@...k-chips.com, linux-arm-kernel@...ts.infradead.org,
	linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: rockchip: change PLL setting for better clock jitter

Am Donnerstag, 9. Oktober 2014, 22:23:57 schrieb Kever Yang:
> dclk_vop0/1 is the source of HDMI TMDS clock in rk3288, usually we
> use 594MHz for clock source of dclk_vop0/1.
> 
> HDMI CTS 7-9 require TMDS Clock jitter is lower than 0.25*Tbit:
> TMDS clock(MHz)		CTS require jitter (ps)
> 	297		84.2
> 	148.5		168
> 	74.25		336
> 	27		1247
> 
> PLL BW and VCO frequency effects the jitter of PLL output clock,
> clock jitter is better if BW is lower or VCO frequency is higher.
> 
> If PLL use default setting of RK3066_PLL_RATE( 594000000, 2, 198, 4),
> the TMDS Clock jitter is higher than 250ps, which means we can't
> pass the test when TMDS clock is 297MHz or 148.5MHz.
> 
> If we use RK3066_PLL_RATE_BWADJ(594000000, 1, 198, 8, 1),
> the TMDS Clock jitter is about 60ps and we can pass all test case.
> 
> So we need this patch to make hdmi si test pass.
> 
> Signed-off-by: Kever Yang <kever.yang@...k-chips.com>

I've applied this to my v3.19-clk branch with Dougs Review-Tag.


Heiko
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