linux-kernel - Re: [PATCH v3 1/7] clk: divider: add flag to limit possible dividers to even numbers

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Date:	Tue, 11 Jun 2013 11:57:50 -0700
From:	Mike Turquette <mturquette@...aro.org>
To:	Heiko Stübner <heiko@...ech.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Seungwon Jeon <tgih.jun@...sung.com>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Chris Ball <cjb@...top.org>, linux-mmc@...r.kernel.org,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <rob.herring@...xeda.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	devicetree-discuss@...ts.ozlabs.org,
	Russell King <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: [PATCH v3 1/7] clk: divider: add flag to limit possible dividers to even
 numbers

Quoting Heiko Stübner (2013-06-11 04:29:32)
> SoCs like the Rockchip Cortex-A9 ones contain divider some clocks
> that use the regular mechanisms for storage but allow only even
> dividers and 1 to be used.
> 
> Therefore add a flag that lets _is_valid_div limit the valid dividers
> to these values. _get_maxdiv is also adapted to return even values
> for the CLK_DIVIDER_ONE_BASED case.
> 
> Signed-off-by: Heiko Stuebner <heiko@...ech.de>
> ---
>  drivers/clk/clk-divider.c    |   14 ++++++++++++--
>  include/linux/clk-provider.h |    2 ++
>  2 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
> index ce5cfe9..bdee7cf 100644
> --- a/drivers/clk/clk-divider.c
> +++ b/drivers/clk/clk-divider.c
> @@ -45,8 +45,16 @@ static unsigned int _get_table_maxdiv(const struct clk_div_table *table)
>  
>  static unsigned int _get_maxdiv(struct clk_divider *divider)
>  {
> -       if (divider->flags & CLK_DIVIDER_ONE_BASED)
> -               return div_mask(divider);
> +       if (divider->flags & CLK_DIVIDER_ONE_BASED) {
> +               unsigned int div = div_mask(divider);
> +
> +               /* decrease to even number */
> +               if (divider->flags & CLK_DIVIDER_EVEN)
> +                       div--;
> +
> +               return div;
> +       }
> +
>         if (divider->flags & CLK_DIVIDER_POWER_OF_TWO)
>                 return 1 << div_mask(divider);
>         if (divider->table)
> @@ -141,6 +149,8 @@ static bool _is_valid_div(struct clk_divider *divider, unsigned int div)
>                 return is_power_of_2(div);
>         if (divider->table)
>                 return _is_valid_table_div(divider->table, div);
> +       if (divider->flags & CLK_DIVIDER_EVEN && div != 1 && (div % 2) != 0)

Is it correct to check for 'div != 1' here?  Wouldn't that check only be
valid in the presence of CLK_DIVIDER_ONE_BASED?

Maybe something like this would be more correct:

	if (divider->flags & CLK_DIVIDER_EVEN && (div % 2) != 0) {
		if (divider->flags & CLK_DIVIDER_ONE_BASED && div == 1)
			return true;
		return false;
	}

Regards,
Mike

> +               return false;
>         return true;
>  }
>  
> diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
> index 1ec14a7..bd52e52 100644
> --- a/include/linux/clk-provider.h
> +++ b/include/linux/clk-provider.h
> @@ -266,6 +266,7 @@ struct clk_div_table {
>   *   of this register, and mask of divider bits are in higher 16-bit of this
>   *   register.  While setting the divider bits, higher 16-bit should also be
>   *   updated to indicate changing divider bits.
> + * CLK_DIVIDER_EVEN - only allow even divider values
>   */
>  struct clk_divider {
>         struct clk_hw   hw;
> @@ -281,6 +282,7 @@ struct clk_divider {
>  #define CLK_DIVIDER_POWER_OF_TWO       BIT(1)
>  #define CLK_DIVIDER_ALLOW_ZERO         BIT(2)
>  #define CLK_DIVIDER_HIWORD_MASK                BIT(3)
> +#define CLK_DIVIDER_EVEN               BIT(4)
>  
>  extern const struct clk_ops clk_divider_ops;
>  struct clk *clk_register_divider(struct device *dev, const char *name,
> -- 
> 1.7.2.3
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