linux-kernel - Re: [PATCH tty v1 29/74] serial: imx: Use port lock wrappers

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Date:   Fri, 15 Sep 2023 22:21:22 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Marek Vasut <marex@...x.de>, Petr Mladek <pmladek@...e.com>,
        Fabio Estevam <festevam@...il.com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Rob Herring <robh@...nel.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
        Sergey Organov <sorganov@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        linux-serial@...r.kernel.org,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Shawn Guo <shawnguo@...nel.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH tty v1 29/74] serial: imx: Use port lock wrappers

On Thu, Sep 14, 2023 at 08:43:46PM +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>

This lacks a Signed-off line by John.

Otherwise looks fine to me.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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