linux-kernel - Re: [PATCH 1/2] serial: qcom-geni: fix opp vote on shutdown

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Message-ID: <e99b5975-b770-5460-1ce4-cd4eb1a50291@linaro.org>
Date:   Fri, 14 Jul 2023 16:29:08 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Johan Hovold <johan+linaro@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-arm-msm@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Rajendra Nayak <quic_rjendra@...cinc.com>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: Re: [PATCH 1/2] serial: qcom-geni: fix opp vote on shutdown

On 14.07.2023 15:02, Johan Hovold wrote:
> The operating-performance-point vote needs to be dropped when shutting
> down the port to avoid wasting power by keeping resources like power
> domains in an unnecessarily high performance state (e.g. when a UART
> connected Bluetooth controller is not in use).
> 
> Fixes: a5819b548af0 ("tty: serial: qcom_geni_serial: Use OPP API to set clk/perf state")
> Cc: stable@...r.kernel.org      # 5.9
> Cc: Rajendra Nayak <quic_rjendra@...cinc.com>
> Cc: Matthias Kaehlcke <mka@...omium.org>
> Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
> ---
I don't know a whole lot about this subsystem, but the PM call has
a pointer to uport which already contains this clock rate.. Is it
zeroed out by the core before we reach it, which would prevent us
from reusing it?

Konrad
>  drivers/tty/serial/qcom_geni_serial.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
> index b825b05e6137..8be896dbaa88 100644
> --- a/drivers/tty/serial/qcom_geni_serial.c
> +++ b/drivers/tty/serial/qcom_geni_serial.c
> @@ -126,6 +126,7 @@ struct qcom_geni_serial_port {
>  	dma_addr_t rx_dma_addr;
>  	bool setup;
>  	unsigned int baud;
> +	unsigned long clk_rate;
>  	void *rx_buf;
>  	u32 loopback;
>  	bool brk;
> @@ -1249,6 +1250,7 @@ static void qcom_geni_serial_set_termios(struct uart_port *uport,
>  			baud * sampling_rate, clk_rate, clk_div);
>  
>  	uport->uartclk = clk_rate;
> +	port->clk_rate = clk_rate;
>  	dev_pm_opp_set_rate(uport->dev, clk_rate);
>  	ser_clk_cfg = SER_CLK_EN;
>  	ser_clk_cfg |= clk_div << CLK_DIV_SHFT;
> @@ -1513,10 +1515,13 @@ static void qcom_geni_serial_pm(struct uart_port *uport,
>  
>  	if (new_state == UART_PM_STATE_ON && old_state == UART_PM_STATE_OFF) {
>  		geni_icc_enable(&port->se);
> +		if (port->clk_rate)
> +			dev_pm_opp_set_rate(uport->dev, port->clk_rate);
>  		geni_se_resources_on(&port->se);
>  	} else if (new_state == UART_PM_STATE_OFF &&
>  			old_state == UART_PM_STATE_ON) {
>  		geni_se_resources_off(&port->se);
> +		dev_pm_opp_set_rate(uport->dev, 0);
>  		geni_icc_disable(&port->se);
>  	}
>  }