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Message-ID: <20230914191652.GB1487598@hu-bjorande-lv.qualcomm.com>
Date: Thu, 14 Sep 2023 12:16:52 -0700
From: Bjorn Andersson <quic_bjorande@...cinc.com>
To: John Ogness <john.ogness@...utronix.de>
CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jiri Slaby <jirislaby@...nel.org>,
<linux-serial@...r.kernel.org>, Petr Mladek <pmladek@...e.com>,
Thomas Gleixner <tglx@...utronix.de>,
<linux-kernel@...r.kernel.org>, Andy Gross <agross@...nel.org>,
Bjorn Andersson <andersson@...nel.org>,
Konrad Dybcio <konrad.dybcio@...aro.org>,
<linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH tty v1 49/74] serial: qcom-geni: Use port lock wrappers
On Thu, Sep 14, 2023 at 08:44:06PM +0206, John Ogness wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
>
> When a serial port is used for kernel console output, then all
> modifications to the UART registers which are done from other contexts,
> e.g. getty, termios, are interference points for the kernel console.
>
> So far this has been ignored and the printk output is based on the
> principle of hope. The rework of the console infrastructure which aims to
> support threaded and atomic consoles, requires to mark sections which
> modify the UART registers as unsafe. This allows the atomic write function
> to make informed decisions and eventually to restore operational state. It
> also allows to prevent the regular UART code from modifying UART registers
> while printk output is in progress.
>
> All modifications of UART registers are guarded by the UART port lock,
> which provides an obvious synchronization point with the console
> infrastructure.
>
> To avoid adding this functionality to all UART drivers, wrap the
> spin_[un]lock*() invocations for uart_port::lock into helper functions
> which just contain the spin_[un]lock*() invocations for now. In a
> subsequent step these helpers will gain the console synchronization
> mechanisms.
>
> Converted with coccinelle. No functional change.
>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Bjorn Andersson <quic_bjorande@...cinc.com>
> ---
> drivers/tty/serial/qcom_geni_serial.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
> index b8aa4c1293ba..7e78f97e8f43 100644
> --- a/drivers/tty/serial/qcom_geni_serial.c
> +++ b/drivers/tty/serial/qcom_geni_serial.c
> @@ -482,9 +482,9 @@ static void qcom_geni_serial_console_write(struct console *co, const char *s,
>
> uport = &port->uport;
> if (oops_in_progress)
> - locked = spin_trylock_irqsave(&uport->lock, flags);
> + locked = uart_port_trylock_irqsave(uport, &flags);
> else
> - spin_lock_irqsave(&uport->lock, flags);
> + uart_port_lock_irqsave(uport, &flags);
>
> geni_status = readl(uport->membase + SE_GENI_STATUS);
>
> @@ -520,7 +520,7 @@ static void qcom_geni_serial_console_write(struct console *co, const char *s,
> qcom_geni_serial_setup_tx(uport, port->tx_remaining);
>
> if (locked)
> - spin_unlock_irqrestore(&uport->lock, flags);
> + uart_port_unlock_irqrestore(uport, flags);
> }
>
> static void handle_rx_console(struct uart_port *uport, u32 bytes, bool drop)
> @@ -970,7 +970,7 @@ static irqreturn_t qcom_geni_serial_isr(int isr, void *dev)
> if (uport->suspended)
> return IRQ_NONE;
>
> - spin_lock(&uport->lock);
> + uart_port_lock(uport);
>
Nice, now this no longer look unbalanced with the unlock in
uart_port_unlock_irqrestore().
Regards,
Bjorn
> m_irq_status = readl(uport->membase + SE_GENI_M_IRQ_STATUS);
> s_irq_status = readl(uport->membase + SE_GENI_S_IRQ_STATUS);
> --
> 2.39.2
>
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