linux-kernel - Re: [PATCH v2 1/3] clk: qcom: gdsc: Fix the handling of PWRSTS

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Message-ID: <20220916190545.4yadf4effjeipawu@builder.lan>
Date:   Fri, 16 Sep 2022 14:05:45 -0500
From:   Bjorn Andersson <andersson@...nel.org>
To:     Rajendra Nayak <quic_rjendra@...cinc.com>
Cc:     agross@...nel.org, konrad.dybcio@...ainline.org,
        mturquette@...libre.com, sboyd@...nel.org, mka@...omium.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        johan+linaro@...nel.org, quic_kriskura@...cinc.com,
        dianders@...omium.org, linux-clk@...r.kernel.org,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>
Subject: Re: [PATCH v2 1/3] clk: qcom: gdsc: Fix the handling of PWRSTS_RET
 support

On Fri, Sep 16, 2022 at 03:54:15PM +0530, Rajendra Nayak wrote:
> GDSCs cannot be transitioned into a Retention state in SW.
> When either the RETAIN_MEM bit, or both the RETAIN_MEM and
> RETAIN_PERIPH bits are set, and the GDSC is left ON, the HW
> takes care of retaining the memory/logic for the domain when
> the parent domain transitions to low power state.
> The existing logic handling the PWRSTS_RET seems to set the
> RETAIN_MEM/RETAIN_PERIPH bits but then explicitly turns the
> GDSC OFF as part of _gdsc_disable(). Fix that by leaving the
> GDSC in ON state.
> 
> Signed-off-by: Rajendra Nayak <quic_rjendra@...cinc.com>
> Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@...ainline.org>

Reviewed-by: Bjorn Andersson <andersson@...nel.org>

Regards,
Bjorn

> ---
> No changes in v2: 
> 
> There are a few existing users of PWRSTS_RET and I am not
> sure if they would be impacted with this change
> 
> 1. mdss_gdsc in mmcc-msm8974.c, I am expecting that the
> gdsc is actually transitioning to OFF and might be left
> ON as part of this change, atleast till we hit system wide
> low power state.
> If we really leak more power because of this
> change, the right thing to do would be to update .pwrsts for
> mdss_gdsc to PWRSTS_OFF_ON instead of PWRSTS_RET_ON
> I dont have a msm8974 hardware, so if anyone who has can report
> any issues I can take a look further on how to fix it.
> 
> 2. gpu_gx_gdsc in gpucc-msm8998.c and
>    gpu_gx_gdsc in gpucc-sdm660.c
> Both of these seem to add support for 3 power state
> OFF, RET and ON, however I dont see any logic in gdsc
> driver to handle 3 different power states.
> So I am expecting that these are infact just transitioning
> between ON and OFF and RET state is never really used.
> The ideal fix for them would be to just update their resp.
> .pwrsts to PWRSTS_OFF_ON only.
> 
>  drivers/clk/qcom/gdsc.c | 10 ++++++++++
>  drivers/clk/qcom/gdsc.h |  5 +++++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/drivers/clk/qcom/gdsc.c b/drivers/clk/qcom/gdsc.c
> index d3244006c661..ccf63771e852 100644
> --- a/drivers/clk/qcom/gdsc.c
> +++ b/drivers/clk/qcom/gdsc.c
> @@ -368,6 +368,16 @@ static int _gdsc_disable(struct gdsc *sc)
>  	if (sc->pwrsts & PWRSTS_OFF)
>  		gdsc_clear_mem_on(sc);
>  
> +	/*
> +	 * If the GDSC supports only a Retention state, apart from ON,
> +	 * leave it in ON state.
> +	 * There is no SW control to transition the GDSC into
> +	 * Retention state. This happens in HW when the parent
> +	 * domain goes down to a Low power state
> +	 */
> +	if (sc->pwrsts == PWRSTS_RET_ON)
> +		return 0;
> +
>  	ret = gdsc_toggle_logic(sc, GDSC_OFF);
>  	if (ret)
>  		return ret;
> diff --git a/drivers/clk/qcom/gdsc.h b/drivers/clk/qcom/gdsc.h
> index 5de48c9439b2..981a12c8502d 100644
> --- a/drivers/clk/qcom/gdsc.h
> +++ b/drivers/clk/qcom/gdsc.h
> @@ -49,6 +49,11 @@ struct gdsc {
>  	const u8			pwrsts;
>  /* Powerdomain allowable state bitfields */
>  #define PWRSTS_OFF		BIT(0)
> +/*
> + * There is no SW control to transition a GDSC into
> + * PWRSTS_RET. This happens in HW when the parent
> + * domain goes down to a low power state
> + */
>  #define PWRSTS_RET		BIT(1)
>  #define PWRSTS_ON		BIT(2)
>  #define PWRSTS_OFF_ON		(PWRSTS_OFF | PWRSTS_ON)
> -- 
> 2.17.1
>