linux-kernel - Re: [PATCH tty v1 41/74] serial: msm: Use port lock wrappers

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Message-ID: <20230914191328.GA1487598@hu-bjorande-lv.qualcomm.com>
Date:   Thu, 14 Sep 2023 12:13:28 -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 41/74] serial: msm: Use port lock wrappers

On Thu, Sep 14, 2023 at 08:43:58PM +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>

Regards,
Bjorn