linux-kernel - Re: [PATCH V5 RESEND 3/5] clk: qcom: gdsc: Add set and get hwmode callbacks to switch GDSC mode

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Message-ID: <e70e0379-cab0-4586-825e-ade6775ca67c@linaro.org>
Date: Wed, 24 Apr 2024 00:48:50 +0100
From: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To: Jagadeesh Kona <quic_jkona@...cinc.com>,
 Bjorn Andersson <andersson@...nel.org>,
 Michael Turquette <mturquette@...libre.com>, Stephen Boyd
 <sboyd@...nel.org>, Stanimir Varbanov <stanimir.k.varbanov@...il.com>,
 Vikash Garodia <quic_vgarodia@...cinc.com>,
 Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
 Mauro Carvalho Chehab <mchehab@...nel.org>,
 Ulf Hansson <ulf.hansson@...aro.org>, "Rafael J . Wysocki"
 <rafael@...nel.org>, Kevin Hilman <khilman@...nel.org>,
 Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Konrad Dybcio <konrad.dybcio@...aro.org>, Andy Gross <agross@...nel.org>,
 Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
 Abel Vesa <abel.vesa@...aro.org>
Cc: linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
 linux-pm@...r.kernel.org, Taniya Das <quic_tdas@...cinc.com>,
 Satya Priya Kakitapalli <quic_skakitap@...cinc.com>,
 Imran Shaik <quic_imrashai@...cinc.com>,
 Ajit Pandey <quic_ajipan@...cinc.com>
Subject: Re: [PATCH V5 RESEND 3/5] clk: qcom: gdsc: Add set and get hwmode
 callbacks to switch GDSC mode

On 13/04/2024 16:20, Jagadeesh Kona wrote:
> Some GDSC client drivers require the GDSC mode to be switched dynamically
> to HW mode at runtime to gain the power benefits. Typically such client
> drivers require the GDSC to be brought up in SW mode initially to enable
> the required dependent clocks and configure the hardware to proper state.
> Once initial hardware set up is done, they switch the GDSC to HW mode to
> save power. At the end of usecase, they switch the GDSC back to SW mode
> and disable the GDSC.
> 
> Introduce HW_CTRL_TRIGGER flag to register the set_hwmode_dev and
> get_hwmode_dev callbacks for GDSC's whose respective client drivers
> require the GDSC mode to be switched dynamically at runtime using
> dev_pm_genpd_set_hwmode() API.
> 
> Signed-off-by: Jagadeesh Kona <quic_jkona@...cinc.com>
> Signed-off-by: Abel Vesa <abel.vesa@...aro.org>
> ---
>   drivers/clk/qcom/gdsc.c | 37 +++++++++++++++++++++++++++++++++++++
>   drivers/clk/qcom/gdsc.h |  1 +
>   2 files changed, 38 insertions(+)
> 
> diff --git a/drivers/clk/qcom/gdsc.c b/drivers/clk/qcom/gdsc.c
> index df9618ab7eea..c5f6be8181d8 100644
> --- a/drivers/clk/qcom/gdsc.c
> +++ b/drivers/clk/qcom/gdsc.c
> @@ -363,6 +363,39 @@ static int gdsc_disable(struct generic_pm_domain *domain)
>   	return 0;
>   }
>   
> +static int gdsc_set_hwmode(struct generic_pm_domain *domain, struct device *dev, bool mode)
> +{
> +	struct gdsc *sc = domain_to_gdsc(domain);
> +	int ret;
> +
> +	ret = gdsc_hwctrl(sc, mode);
> +	if (ret)
> +		return ret;
> +
> +	/* Wait for 1usec for mode transition to properly complete */
> +	udelay(1);

A delay I suspect you don't need - if the HW spec says "takes 1 usec for 
this to take effect" that's 1 usec from io write completion from APSS to 
another system agent.

You poll for the state transition down below anyway.

I'd be pretty certain that's a redundant delay.

> +
> +	/*
> +	 * When GDSC is switched to HW mode, HW can disable the GDSC.
> +	 * When GDSC is switched back to SW mode, the GDSC will be enabled
> +	 * again, hence need to poll for GDSC to complete the power up.
> +	 */
> +	if (!mode)
> +		return gdsc_poll_status(sc, GDSC_ON);
> +
> +	return 0;
> +}

Other than that, seems fine.

Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@...aro.org>