linux-kernel - Re: [PATCH v1 1/6] clk: rockchip: Add supprot to limit input rate for fractional divider

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Date:   Fri, 12 Apr 2019 13:52:25 +0200
From:   Heiko Stübner <heiko@...ech.de>
To:     Elaine Zhang <zhangqing@...k-chips.com>
Cc:     mturquette@...libre.com, sboyd@...nel.org,
        linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org,
        xxx@...k-chips.com, xf@...k-chips.com, huangtao@...k-chips.com,
        Finley Xiao <finley.xiao@...k-chips.com>,
        christoph.muellner@...obroma-systems.com
Subject: Re: [PATCH v1 1/6] clk: rockchip: Add supprot to limit input rate for fractional divider

Hi Elaine,

Am Mittwoch, 3. April 2019, 11:42:24 CEST schrieb Elaine Zhang:
> From: Finley Xiao <finley.xiao@...k-chips.com>
> 
> From Rockchips fractional divider usage, some clocks can be generated
> by fractional divider, but the input clock frequency of fractional
> divider should be less than a specified value.
> 
> Signed-off-by: Finley Xiao <finley.xiao@...k-chips.com>
> Signed-off-by: Elaine Zhang <zhangqing@...k-chips.com>

can you tell me where these maximum input values come from?

I talked to Christoph from Theobroma (Cc'ed) last week and he mentioned
that they're using the fractional divider with a higher input frequency
to create a very specific frequency [some details are gone from my memory
though] they can't get otherwise.

So I really don't want to break their working setup by introducing barriers
that are not strictly necessary.

@Christoph: can you describe the bits from your fractional setup that
I've forgotten please?


Thanks
Heiko


> diff --git a/drivers/clk/rockchip/clk-px30.c b/drivers/clk/rockchip/clk-px30.c
> index 601a77f1af78..ccabce35580b 100644
> --- a/drivers/clk/rockchip/clk-px30.c
> +++ b/drivers/clk/rockchip/clk-px30.c
> @@ -21,6 +21,7 @@
>  #include "clk.h"
>  
>  #define PX30_GRF_SOC_STATUS0		0x480
> +#define PX30_FRAC_MAX_PRATE		600000000


> diff --git a/drivers/clk/rockchip/clk-rk3368.c b/drivers/clk/rockchip/clk-rk3368.c
> index 7c4d242f19c1..67c2da5e7d61 100644
> --- a/drivers/clk/rockchip/clk-rk3368.c
> +++ b/drivers/clk/rockchip/clk-rk3368.c
> @@ -20,6 +20,9 @@
>  #include "clk.h"
>  
>  #define RK3368_GRF_SOC_STATUS0	0x480
> +#define RK3368_I2S_FRAC_MAX_PRATE       600000000
> +#define RK3368_UART_FRAC_MAX_PRATE	600000000
> +#define RK3368_SPDIF_FRAC_MAX_PRATE	600000000

> diff --git a/drivers/clk/rockchip/clk-rk3399.c b/drivers/clk/rockchip/clk-rk3399.c
> index 5a628148f3f0..1d81382bd3e0 100644
> --- a/drivers/clk/rockchip/clk-rk3399.c
> +++ b/drivers/clk/rockchip/clk-rk3399.c
> @@ -21,6 +21,12 @@
>  #include <dt-bindings/clock/rk3399-cru.h>
>  #include "clk.h"
>  
> +#define RK3399_I2S_FRAC_MAX_PRATE       600000000
> +#define RK3399_UART_FRAC_MAX_PRATE	600000000
> +#define RK3399_SPDIF_FRAC_MAX_PRATE	600000000
> +#define RK3399_VOP_FRAC_MAX_PRATE	600000000
> +#define RK3399_WIFI_FRAC_MAX_PRATE	600000000
> +