linux-kernel - Re: [PATCH v4 2/4] clk: tegra: refactor 7.1 div calculation

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Message-ID: <5805047f-4099-db34-0759-42e4a9e11629@nvidia.com>
Date:   Tue, 10 Jul 2018 17:17:05 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Aapo Vienamo <avienamo@...dia.com>,
        Peter De Schrijver <pdeschrijver@...dia.com>
CC:     Prashant Gaikwad <pgaikwad@...dia.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        <linux-kernel@...r.kernel.org>, <linux-clk@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v4 2/4] clk: tegra: refactor 7.1 div calculation


On 09/07/18 17:38, Aapo Vienamo wrote:
> From: Peter De Schrijver <pdeschrijver@...dia.com>
> 
> Move this to a separate file so it can be used to calculate the sdmmc
> clock dividers.

Sorry for not commenting sooner, but what is the motivation for moving
this to its own file? I don't see why we need to do this in order to use
elsewhere. Furthermore, the original file is quite aptly named 'clk-divider.c'
and now we have a div71.c which seems quite specific.
> Signed-off-by: Peter De-Schrijver <pdeschrijver@...dia.com>
> Signed-off-by: Aapo Vienamo <avienamo@...dia.com>
> Acked-by: Peter De Schrijver <pdeschrijver@...dia.com>
> ---
>  drivers/clk/tegra/Makefile      |  1 +
>  drivers/clk/tegra/clk-divider.c | 30 +++++-----------------------
>  drivers/clk/tegra/clk.h         |  3 +++
>  drivers/clk/tegra/div71.c       | 43 +++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 52 insertions(+), 25 deletions(-)
>  create mode 100644 drivers/clk/tegra/div71.c
> 
> diff --git a/drivers/clk/tegra/Makefile b/drivers/clk/tegra/Makefile
> index b716923..6d4f563 100644
> --- a/drivers/clk/tegra/Makefile
> +++ b/drivers/clk/tegra/Makefile
> @@ -24,3 +24,4 @@ obj-$(CONFIG_ARCH_TEGRA_132_SOC)	+= clk-tegra124.o
>  obj-y					+= cvb.o
>  obj-$(CONFIG_ARCH_TEGRA_210_SOC)	+= clk-tegra210.o
>  obj-$(CONFIG_CLK_TEGRA_BPMP)		+= clk-bpmp.o
> +obj-y					+= div71.o
> diff --git a/drivers/clk/tegra/clk-divider.c b/drivers/clk/tegra/clk-divider.c
> index 16e0aee..ad87858 100644
> --- a/drivers/clk/tegra/clk-divider.c
> +++ b/drivers/clk/tegra/clk-divider.c
> @@ -32,35 +32,15 @@
>  static int get_div(struct tegra_clk_frac_div *divider, unsigned long rate,
>  		   unsigned long parent_rate)
>  {
> -	u64 divider_ux1 = parent_rate;
> -	u8 flags = divider->flags;
> -	int mul;
> -
> -	if (!rate)
> -		return 0;
> -
> -	mul = get_mul(divider);
> -
> -	if (!(flags & TEGRA_DIVIDER_INT))
> -		divider_ux1 *= mul;
> -
> -	if (flags & TEGRA_DIVIDER_ROUND_UP)
> -		divider_ux1 += rate - 1;
> -
> -	do_div(divider_ux1, rate);
> -
> -	if (flags & TEGRA_DIVIDER_INT)
> -		divider_ux1 *= mul;
> +	int div;
>  
> -	divider_ux1 -= mul;
> +	div = div71_get(rate, parent_rate, divider->width, divider->frac_width,
> +			divider->flags);
>  
> -	if ((s64)divider_ux1 < 0)
> +	if (div < 0)
>  		return 0;
>  
> -	if (divider_ux1 > get_max_div(divider))
> -		return get_max_div(divider);
> -
> -	return divider_ux1;
> +	return div;
>  }
>  
>  static unsigned long clk_frac_div_recalc_rate(struct clk_hw *hw,
> diff --git a/drivers/clk/tegra/clk.h b/drivers/clk/tegra/clk.h
> index e3b9c22..149cc70 100644
> --- a/drivers/clk/tegra/clk.h
> +++ b/drivers/clk/tegra/clk.h
> @@ -812,6 +812,9 @@ extern tegra_clk_apply_init_table_func tegra_clk_apply_init_table;
>  int tegra_pll_wait_for_lock(struct tegra_clk_pll *pll);
>  u16 tegra_pll_get_fixed_mdiv(struct clk_hw *hw, unsigned long input_rate);
>  int tegra_pll_p_div_to_hw(struct tegra_clk_pll *pll, u8 p_div);
> +int div71_get(unsigned long rate, unsigned parent_rate, u8 width,
> +	      u8 frac_width, u8 flags);
> +
>  
>  /* Combined read fence with delay */
>  #define fence_udelay(delay, reg)	\
> diff --git a/drivers/clk/tegra/div71.c b/drivers/clk/tegra/div71.c
> new file mode 100644
> index 0000000..1eecc84
> --- /dev/null
> +++ b/drivers/clk/tegra/div71.c
> @@ -0,0 +1,43 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2018, NVIDIA CORPORATION.  All rights reserved.
> + */
> +
> +#include <asm/div64.h>
> +
> +#include "clk.h"
> +
> +#define div_mask(w) ((1 << (w)) - 1)
> +
> +int div71_get(unsigned long rate, unsigned parent_rate, u8 width,
> +	      u8 frac_width, u8 flags)
> +{
> +	u64 divider_ux1 = parent_rate;
> +	int mul;
> +
> +	if (!rate)
> +		return 0;
> +
> +	mul = 1 << frac_width;
> +
> +	if (!(flags & TEGRA_DIVIDER_INT))
> +		divider_ux1 *= mul;
> +
> +	if (flags & TEGRA_DIVIDER_ROUND_UP)
> +		divider_ux1 += rate - 1;
> +
> +	do_div(divider_ux1, rate);
> +
> +	if (flags & TEGRA_DIVIDER_INT)
> +		divider_ux1 *= mul;
> +
> +	if (divider_ux1 < mul)
> +		return 0;
> +
> +	divider_ux1 -= mul;
> +
> +	if (divider_ux1 > div_mask(width))
> +		return div_mask(width);
> +
> +	return divider_ux1;
> +}

I don't see anything in the above that makes this 7.1? It seems that the
fractional width is being passed meaning it could be m.n unless I am missing
something.

Cheers
Jon

-- 
nvpublic