linux-kernel - Re: [PATCH] clk: qcom: gdsc: Ensure regulator init state matches GDSC state

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Message-ID: <162494849279.2516444.9302337933628102536@swboyd.mtv.corp.google.com>
Date:   Mon, 28 Jun 2021 23:34:52 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        Vinod Koul <vkoul@...nel.org>, dmitry.baryshkov@...aro.org
Cc:     linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] clk: qcom: gdsc: Ensure regulator init state matches GDSC state

Quoting Bjorn Andersson (2021-06-25 15:54:14)
> As GDSCs are registered and found to be already enabled
> gdsc_toggle_logic() will be invoked for votable GDSCs and ensure that
> the vote is matching the hardware state. Part of this the related
> regulator will be enabled.
> 
> But for non-votable GDSCs the regulator and GDSC status will be out of
> sync and as the GDSC is later disabled regulator_disable() will face an
> unbalanced enable-count, or something might turn off the supply under
> the feet of the GDSC.
> 
> So ensure that the regulator is enabled even for non-votable GDSCs.
> 
> Cc: stable@...r.kernel.org
> Fixes: 37416e554961 ("clk: qcom: gdsc: Handle GDSC regulator supplies")
> Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> ---
>  drivers/clk/qcom/gdsc.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/clk/qcom/gdsc.c b/drivers/clk/qcom/gdsc.c
> index 51ed640e527b..f7e7759cdb90 100644
> --- a/drivers/clk/qcom/gdsc.c
> +++ b/drivers/clk/qcom/gdsc.c
> @@ -359,10 +359,17 @@ static int gdsc_init(struct gdsc *sc)
>  
>         /*
>          * Votable GDSCs can be ON due to Vote from other masters.
> -        * If a Votable GDSC is ON, make sure we have a Vote.
> +        * If a Votable GDSC is ON, make sure we have a Vote. If
> +        * non-votable, ensure that the supply is kept enabled (as
> +        * is done by gdsc_enable).
>          */
> -       if ((sc->flags & VOTABLE) && on)
> +       if ((sc->flags & VOTABLE) && on) {
>                 gdsc_enable(&sc->pd);
> +       } else if (on) {
> +               ret = regulator_enable(sc->rsupply);
> +               if (ret < 0)
> +                       return ret;

Looking at this makes me think we've messed something up with
gdsc_enable() being called or cherry-picking the regulator enable (and
other stuff in this gdsc_init()) out of the enable path. Maybe we should
have a followup patch that replaces the gdsc_enable() with
gdsc_toggle_logic(sc, GDSC_ON) so that we know it isn't doing anything
else during init like asserting a reset when presumably all we want to
do is toggle the enable bit to assert our vote.

And I notice that we already call gdsc_toggle_logic() in gdsc_init(), so
then we'll have a double regulator_enable() in the case of PWRSTS_ON?
And then if the flag is ALWAYS_ON we'll call regulator_enable() yet
again, but luckily only if it isn't on initially, phew! This code is
quite twisted.

It would be super nice to make it more like

	if (on) {
		/* It was on in hardware, sync kernel state */
		regulator_enable();

		if (votable)
			write bit, why do any wait?

		if (retain ff)
			write bit
	} else if (always_on) {
		/* Force on */
		gdsc_enable();
		on = true;
	}

	if (on || ...)

> +       }
>  
>         /*
>          * Make sure the retain bit is set if the GDSC is already on, otherwise