linux-kernel - Re: [PATCH v2 2/8] clk: Introduce CLK_ASSUME_ENABLED_WHEN

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Message-ID: <YnFEGzTQMsNpczai@builder.lan>
Date:   Tue, 3 May 2022 10:02:51 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Robert Foss <robert.foss@...aro.org>
Cc:     agross@...nel.org, mturquette@...libre.com, sboyd@...nel.org,
        robh+dt@...nel.org, krzk+dt@...nel.org, jonathan@...ek.ca,
        tdas@...eaurora.org, anischal@...eaurora.org,
        linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Subject: Re: [PATCH v2 2/8] clk: Introduce CLK_ASSUME_ENABLED_WHEN_UNUSED

On Tue 03 May 08:04 CDT 2022, Robert Foss wrote:

> From: Bjorn Andersson <bjorn.andersson@...aro.org>
> 
> 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.
> 
> Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> ---
> 

I discussed this with Stephen a while ago and we agreed that in a
sufficiently complex system with kernel modules booting without
clk_ignore_unused simply isn't supported.

We will have to design something better. So please drop this patch from
the series.

Regards,
Bjorn

> Changes since v1
>  - Removed Vinods r-b
> 
> 
>  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 ed119182aa1b..9789ec137219 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -1284,7 +1284,7 @@ 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 c10dc4c659e2..9038022ffebd 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;
> -- 
> 2.34.1
>