linux-kernel - Re: [RFC] clk: Mark HW enabled clocks as enabled in core

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Message-ID: <20210126115105.GD28722@pengutronix.de>
Date:   Tue, 26 Jan 2021 12:51:05 +0100
From:   Sascha Hauer <sha@...gutronix.de>
To:     Abel Vesa <abel.vesa@....com>
Cc:     Mike Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Sascha Hauer <kernel@...gutronix.de>,
        Lucas Stach <l.stach@...gutronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-clk@...r.kernel.org
Subject: Re: [RFC] clk: Mark HW enabled clocks as enabled in core

On Tue, Jan 26, 2021 at 01:21:36PM +0200, Abel Vesa wrote:
> Some clocks are already enabled in HW even before the kernel
> starts to boot. So, in order to make sure that these clocks do not
> get disabled when clk_disable_unused call is done or when
> reparenting clocks, we enable them in core on clock registration.
> Such a clock will have to be registered with CLK_IGNORE_UNUSED flag
> and also needs to have the is_enabled ops implemented.
> 
> Signed-off-by: Abel Vesa <abel.vesa@....com>
> ---
>  drivers/clk/clk.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index 3d751ae5bc70..26d55851cfa5 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -3416,6 +3416,7 @@ static int __clk_core_init(struct clk_core *core)
>  	int ret;
>  	struct clk_core *parent;
>  	unsigned long rate;
> +	bool is_hw_enabled = false;
>  	int phase;
>  
>  	if (!core)
> @@ -3558,12 +3559,20 @@ static int __clk_core_init(struct clk_core *core)
>  		rate = 0;
>  	core->rate = core->req_rate = rate;
>  
> +	/*
> +	 * If the clock has the CLK_IGNORE_UNUSED flag set and it is already
> +	 * enabled in HW, enable it in core too so it won't get accidentally
> +	 * disabled when walking the orphan tree and reparenting clocks
> +	 */
> +	if (core->flags & CLK_IGNORE_UNUSED && core->ops->is_enabled)
> +		is_hw_enabled = clk_core_is_enabled(core);
> +
>  	/*
>  	 * Enable CLK_IS_CRITICAL clocks so newly added critical clocks
>  	 * don't get accidentally disabled when walking the orphan tree and
>  	 * reparenting clocks
>  	 */
> -	if (core->flags & CLK_IS_CRITICAL) {
> +	if (core->flags & CLK_IS_CRITICAL || is_hw_enabled) {
>  		unsigned long flags;
>  
>  		ret = clk_core_prepare(core);

This means that a bootloader enabled clock with CLK_IGNORE_UNUSED flag
can effectively never be disabled because the prepare/enable count is 1
without any user. This is the behaviour we want to have with critical
clocks, but I don't think this is desired for clocks with the
CLK_IGNORE_UNUSED flag.

Sascha

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