linux-kernel - Re: [PATCH] clk: rockchip: fix frac settings of GPLL clock for rk3328

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Date:   Mon, 24 Dec 2018 10:18:22 +0100
From:   Heiko Stuebner <heiko@...ech.de>
To:     Katsuhiro Suzuki <katsuhiro@...suster.net>
Cc:     linux-rockchip@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: rockchip: fix frac settings of GPLL clock for rk3328

Am Samstag, 22. Dezember 2018, 17:42:49 CET schrieb Katsuhiro Suzuki:
> This patch fixes settings of GPLL frequency in fractional mode for
> rk3328. In this mode, FOUTVCO is calcurated by following formula:
>   FOUTVCO = FREF * FBDIV / REFDIV + ((FREF * FRAC / REFDIV) >> 24)
> 
> The problem is in FREF * FRAC >> 24 term. This result always lacks
> one from target value is specified by rate member. For example first
> itme of rk3328_pll_frac_rate originally has
>   - rate  : 1016064000
>   - refdiv: 3
>   - fbdiv : 127
>   - frac  : 134217
>   - FREF * FBDIV / REFDIV        = 1016000000
>   - (FREF * FRAC / REFDIV) >> 24 = 63999
> Thus calculated rate is 1016063999. It seems wrong.
> 
> If frac has 134218 (it is increased 1 from original value), second
> term is 64000. All other items have same situation. So this patch
> adds 1 to frac member in all items of rk3328_pll_frac_rate.
> 
> Signed-off-by: Katsuhiro Suzuki <katsuhiro@...suster.net>

applied for 4.22 with Elaine's Acked-by

Thanks
Heiko