linux-kernel - Re: [PATCH 2/2] clk: fix CLK_SET_RATE

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Date:   Tue, 19 Jun 2018 10:03:58 -0700
From:   Michael Turquette <mturquette@...libre.com>
To:     Jerome Brunet <jbrunet@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>
Cc:     Jerome Brunet <jbrunet@...libre.com>, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-soc@...r.kernel.org,
        David Brown <david.brown@...aro.org>,
        Andy Gross <andy.gross@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Quentin Schulz <quentin.schulz@...e-electrons.com>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>
Subject: Re: [PATCH 2/2] clk: fix CLK_SET_RATE_GATE with clock rate protection

Quoting Jerome Brunet (2018-06-19 06:40:51)
> CLK_SET_RATE_GATE should prevent any operation which may result in a rate
> change or glitch while the clock is prepared/enabled.
> 
> IOW, the following sequence is not allowed anymore with CLK_SET_RATE_GATE:
> * clk_get()
> * clk_prepare_enable()
> * clk_get_rate()
> * clk_set_rate()
> 
> At the moment this is enforced on the leaf clock of the operation, not
> along the tree. This problematic because, if a PLL has the CLK_RATE_GATE,
> it won't be enforced if the clk_set_rate() is called on its child clocks.
> 
> Using clock rate protection, we can now enforce CLK_SET_RATE_GATE along the
> clock tree
> 
> Acked-by: Linus Walleij <linus.walleij@...aro.org>
> Tested-by: Quentin Schulz <quentin.schulz@...e-electrons.com>
> Tested-by: Maxime Ripard <maxime.ripard@...e-electrons.com>
> Signed-off-by: Jerome Brunet <jbrunet@...libre.com>

Applied to clk-core-set-rate-gate.

Thanks,
Mike

> ---
>  drivers/clk/clk.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index 9760b526ca31..97c09243fb21 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -691,6 +691,9 @@ static void clk_core_unprepare(struct clk_core *core)
>             "Unpreparing critical %s\n", core->name))
>                 return;
>  
> +       if (core->flags & CLK_SET_RATE_GATE)
> +               clk_core_rate_unprotect(core);
> +
>         if (--core->prepare_count > 0)
>                 return;
>  
> @@ -765,6 +768,16 @@ static int clk_core_prepare(struct clk_core *core)
>  
>         core->prepare_count++;
>  
> +       /*
> +        * CLK_SET_RATE_GATE is a special case of clock protection
> +        * Instead of a consumer claiming exclusive rate control, it is
> +        * actually the provider which prevents any consumer from making any
> +        * operation which could result in a rate change or rate glitch while
> +        * the clock is prepared.
> +        */
> +       if (core->flags & CLK_SET_RATE_GATE)
> +               clk_core_rate_protect(core);
> +
>         return 0;
>  unprepare:
>         clk_core_unprepare(core->parent);
> @@ -1888,9 +1901,6 @@ static int clk_core_set_rate_nolock(struct clk_core *core,
>         if (clk_core_rate_is_protected(core))
>                 return -EBUSY;
>  
> -       if ((core->flags & CLK_SET_RATE_GATE) && core->prepare_count)
> -               return -EBUSY;
> -
>         /* calculate new rates and get the topmost changed clock */
>         top = clk_calc_new_rates(core, req_rate);
>         if (!top)
> -- 
> 2.14.3
>