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

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Date:	Wed, 29 Oct 2014 10:10:34 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Kever Yang <kever.yang@...k-chips.com>
Cc:	Heiko Stübner <heiko@...ech.de>,
	Mike Turquette <mturquette@...aro.org>,
	Sonny Rao <sonnyrao@...omium.org>,
	Addy Ke <addy.ke@...k-chips.com>,
	Eddie Cai <cf@...k-chips.com>, Jianqun Xu <xjq@...k-chips.com>,
	han jiang <hj@...k-chips.com>,
	Tao Huang <huangtao@...k-chips.com>,
	戴克霖 (Jack) <dkl@...k-chips.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] clk: rockchip: change PLL setting for better clock jitter

Kever,

On Thu, Oct 9, 2014 at 10:23 PM, Kever Yang <kever.yang@...k-chips.com> wrote:
> 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>
> ---
>
>  drivers/clk/rockchip/clk-rk3288.c | 2 +-
>  drivers/clk/rockchip/clk.h        | 9 +++++++++
>  2 files changed, 10 insertions(+), 1 deletion(-)

As per offline discussion, I have now received a TRM (2014-10-22) that
has expanded the valid ranges of the PLLs.  This now looks OK to me.

Reviewed-by: Doug Anderson <dianders@...omium.org>
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