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

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Message-ID: <273d4d8d-8ffd-8d7f-ef82-4287d6256fcc@quicinc.com>
Date:   Wed, 14 Sep 2022 09:37:29 +0530
From:   Rajendra Nayak <quic_rjendra@...cinc.com>
To:     <andersson@...nel.org>, <agross@...nel.org>,
        <konrad.dybcio@...ainline.org>, <mturquette@...libre.com>,
        <sboyd@...nel.org>, <mka@...omium.org>
CC:     <johan+linaro@...nel.org>, <quic_kriskura@...cinc.com>,
        <dianders@...omium.org>, <linux-clk@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        "Krishna chaitanya chundru" <quic_krichai@...cinc.com>
Subject: Re: [PATCH 1/3] clk: qcom: gdsc: Fix the handling of PWRSTS_RET
 support


On 9/1/2022 3:47 PM, 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.

Any thoughts on this patch? We now have at-least one more user,
PCIe [1] that wants to follow in the footsteps of USB and use RET
state to support wake-ups from low power state.

[1] https://lore.kernel.org/lkml/20220913164233.GF25849@workstation/

> 
> Signed-off-by: Rajendra Nayak <quic_rjendra@...cinc.com>
> Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@...ainline.org>
> ---
> 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)