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

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Message-ID: <1587344.DIk9eYpvKM@phil>
Date:   Mon, 24 Dec 2018 08:34:07 +0100
From:   Heiko Stuebner <heiko@...ech.de>
To:     Katsuhiro Suzuki <katsuhiro@...suster.net>,
        Finley Xiao <finley.xiao@...k-chips.com>,
        Elaine Zhang <zhangqing@...k-chips.com>
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

Hi,

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>

so while this sounds all quite right to me, I've added some Rockchip
people that have clock experience to hopefully get an Ack on the
change :-)

@Elaine + Finley: does this explanation and the below change look right?


Thanks
Heiko

> ---
>  drivers/clk/rockchip/clk-rk3328.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/clk/rockchip/clk-rk3328.c b/drivers/clk/rockchip/clk-rk3328.c
> index faa94adb2a37..65ab5c2f48b0 100644
> --- a/drivers/clk/rockchip/clk-rk3328.c
> +++ b/drivers/clk/rockchip/clk-rk3328.c
> @@ -78,17 +78,17 @@ static struct rockchip_pll_rate_table rk3328_pll_rates[] = {
>  
>  static struct rockchip_pll_rate_table rk3328_pll_frac_rates[] = {
>  	/* _mhz, _refdiv, _fbdiv, _postdiv1, _postdiv2, _dsmpd, _frac */
> -	RK3036_PLL_RATE(1016064000, 3, 127, 1, 1, 0, 134217),
> +	RK3036_PLL_RATE(1016064000, 3, 127, 1, 1, 0, 134218),
>  	/* vco = 1016064000 */
> -	RK3036_PLL_RATE(983040000, 24, 983, 1, 1, 0, 671088),
> +	RK3036_PLL_RATE(983040000, 24, 983, 1, 1, 0, 671089),
>  	/* vco = 983040000 */
> -	RK3036_PLL_RATE(491520000, 24, 983, 2, 1, 0, 671088),
> +	RK3036_PLL_RATE(491520000, 24, 983, 2, 1, 0, 671089),
>  	/* vco = 983040000 */
> -	RK3036_PLL_RATE(61440000, 6, 215, 7, 2, 0, 671088),
> +	RK3036_PLL_RATE(61440000, 6, 215, 7, 2, 0, 671089),
>  	/* vco = 860156000 */
> -	RK3036_PLL_RATE(56448000, 12, 451, 4, 4, 0, 9797894),
> +	RK3036_PLL_RATE(56448000, 12, 451, 4, 4, 0, 9797895),
>  	/* vco = 903168000 */
> -	RK3036_PLL_RATE(40960000, 12, 409, 4, 5, 0, 10066329),
> +	RK3036_PLL_RATE(40960000, 12, 409, 4, 5, 0, 10066330),
>  	/* vco = 819200000 */
>  	{ /* sentinel */ },
>  };
>