linux-kernel - Re: [PATCH 1/2] clk: Introduce CLK_ASSUME_ENABLED_WHEN

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Date:   Tue, 7 Dec 2021 10:34:46 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, dmitry.baryshkov@...aro.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH 1/2] clk: Introduce CLK_ASSUME_ENABLED_WHEN_UNUSED

On 02-12-21, 19:54, Bjorn Andersson wrote:
> Some clock implementations doesn't provide means of implementing
> is_enabled(), but still requires to be explicitly disabled when found
> unused as part of clk_disable_unused().
> 
> One such set of clocks are Qualcomm's display RCGs. These can be enabled
> and disabled automatically by the hardware, so it's not possible to
> reliably query their configuration. Further more, these clocks need to
> be disabled when unused, to allow them to be "parked" onto a safe
> parent. Failure to disable the RCG results in the hardware locking up as
> clk_disable_unused() traverses up the tree and turns off its source
> clocks.
> 
> Add a new flag, CLK_ASSUME_ENABLED_BOOT, which clock drivers can use to
> signal that these clocks should be disabled even if they don't implement
> the is_enabled() ops.

I think the name is bit long, but can't think of anything better. Btw
the explanation in log is _very_ good. I think we need to capture this
in the header file below as well.

Reviewed-by: Vinod Koul <vkoul@...nel.org>

> Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> ---
>  drivers/clk/clk.c            | 2 +-
>  include/linux/clk-provider.h | 2 ++
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index f467d63bbf1e..e0bb53cbd4c8 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -1265,7 +1265,7 @@ static void __init clk_disable_unused_subtree(struct clk_core *core)
>  	 * sequence.  call .disable_unused if available, otherwise fall
>  	 * back to .disable
>  	 */
> -	if (clk_core_is_enabled(core)) {
> +	if (clk_core_is_enabled(core) || core->flags & CLK_ASSUME_ENABLED_WHEN_UNUSED) {
>  		trace_clk_disable(core);
>  		if (core->ops->disable_unused)
>  			core->ops->disable_unused(core->hw);
> diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
> index f59c875271a0..7661cce31fa1 100644
> --- a/include/linux/clk-provider.h
> +++ b/include/linux/clk-provider.h
> @@ -32,6 +32,8 @@
>  #define CLK_OPS_PARENT_ENABLE	BIT(12)
>  /* duty cycle call may be forwarded to the parent clock */
>  #define CLK_DUTY_CYCLE_PARENT	BIT(13)
> +/* assume clock is enabled if found unused in late init */
> +#define CLK_ASSUME_ENABLED_WHEN_UNUSED	BIT(14)
>  
>  struct clk;
>  struct clk_hw;
> -- 
> 2.33.1

-- 
~Vinod