LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: John Ogness <john.ogness@linutronix.de>
Cc: Petr Mladek <pmladek@suse.com>,
	Sergey Senozhatsky <senozhatsky@chromium.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jirislaby@kernel.org>,
	Paul Cercueil <paul@crapouillou.net>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	Andrew Jeffery <andrew@aj.id.au>,
	Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
	kuldip dwivedi <kuldip.dwivedi@puresoftware.com>,
	Wang Qing <wangqing@vivo.com>, Andrij Abyzov <aabyzov@slb.com>,
	Johan Hovold <johan@kernel.org>,
	Eddie Huang <eddie.huang@mediatek.com>,
	Claire Chang <tientzu@chromium.org>,
	Hsin-Yi Wang <hsinyi@chromium.org>,
	Zhang Qilong <zhangqilong3@huawei.com>,
	"Maciej W. Rozycki" <macro@orcam.me.uk>,
	Guenter Roeck <linux@roeck-us.net>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Serge Semin <Sergey.Semin@baikalelectronics.ru>,
	"Gustavo A. R. Silva" <gustavoars@kernel.org>,
	Al Cooper <alcooperx@gmail.com>,
	linux-serial@vger.kernel.org, linux-mips@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-mediatek@lists.infradead.org
Subject: Re: [PATCH printk v1 10/10] serial: 8250: implement write_atomic
Date: Tue, 3 Aug 2021 17:07:50 +0300	[thread overview]
Message-ID: <YQlNtr7TNAWtB8XF@smile.fi.intel.com> (raw)
In-Reply-To: <20210803131301.5588-11-john.ogness@linutronix.de>

On Tue, Aug 03, 2021 at 03:19:01PM +0206, John Ogness wrote:
> Implement an NMI-safe write_atomic() console function in order to
> support synchronous console printing.
> 
> Since interrupts need to be disabled during transmit, all usage of
> the IER register is wrapped with access functions that use the
> printk cpulock to synchronize register access while tracking the
> state of the interrupts. This is necessary because write_atomic()
> can be called from an NMI context that has preempted write_atomic().

...

> +static inline void serial8250_set_IER(struct uart_8250_port *up,
> +				      unsigned char ier)
> +{
> +	struct uart_port *port = &up->port;
> +	unsigned long flags;
> +	bool is_console;

> +	is_console = uart_console(port);
> +
> +	if (is_console)
> +		console_atomic_cpu_lock(flags);
> +
> +	serial_out(up, UART_IER, ier);
> +
> +	if (is_console)
> +		console_atomic_cpu_unlock(flags);

I would rewrite it as

	if (uart_console()) {
		console_atomic_cpu_lock(flags);
		serial_out(up, UART_IER, ier);
		console_atomic_cpu_unlock(flags);
	} else {
		serial_out(up, UART_IER, ier);
	}

No additional variable, easier to get the algorithm on the first glance, less
error prone.

> +}

> +static inline unsigned char serial8250_clear_IER(struct uart_8250_port *up)
> +{
> +	struct uart_port *port = &up->port;
> +	unsigned int clearval = 0;
> +	unsigned long flags;
> +	unsigned int prior;
> +	bool is_console;
> +
> +	is_console = uart_console(port);
> +
> +	if (up->capabilities & UART_CAP_UUE)
> +		clearval = UART_IER_UUE;
> +
> +	if (is_console)
> +		console_atomic_cpu_lock(flags);
> +
> +	prior = serial_port_in(port, UART_IER);
> +	serial_port_out(port, UART_IER, clearval);
> +
> +	if (is_console)
> +		console_atomic_cpu_unlock(flags);

Ditto.

> +	return prior;
> +}

...

> +		is_console = uart_console(port);
> +
> +		if (is_console)
> +			console_atomic_cpu_lock(flags);
>  		up->ier = port->serial_in(port, UART_IER);
> +		if (is_console)
> +			console_atomic_cpu_unlock(flags);
> +

I'm wondering why you can't call above function here?

...

> +		is_console = uart_console(p);
> +		if (is_console)
> +			console_atomic_cpu_lock(flags);
>  		ier = p->serial_in(p, UART_IER);
> +		if (is_console)
> +			console_atomic_cpu_unlock(flags);

Ditto.

...

> +	is_console = uart_console(port);
> +
> +	if (is_console)
> +		console_atomic_cpu_lock(flags);
> +
> +	ier = serial_in(up, UART_IER);
> +	serial_out(up, UART_IER, ier & (~mask));
> +
> +	if (is_console)
> +		console_atomic_cpu_unlock(flags);

Ditto.

...

> +	if (uart_console(port))
> +		console_atomic_cpu_lock(flags);
> +
> +	ier = serial_in(up, UART_IER);
> +	serial_out(up, UART_IER, ier | mask);
> +
> +	if (uart_console(port))
> +		console_atomic_cpu_unlock(flags);

Ditto.

Looking into above note, that uart_console(port) can give different results
here, AFAIR.

-- 
With Best Regards,
Andy Shevchenko



  reply	other threads:[~2021-08-03 14:08 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-03 13:12 [PATCH printk v1 00/10] printk: introduce atomic consoles and sync mode John Ogness
2021-08-03 13:12 ` [PATCH printk v1 01/10] printk: relocate printk cpulock functions John Ogness
2021-08-04  9:24   ` Petr Mladek
2021-08-03 13:12 ` [PATCH printk v1 02/10] printk: rename printk cpulock API and always disable interrupts John Ogness
2021-08-04  9:52   ` Petr Mladek
2021-08-03 13:12 ` [PATCH printk v1 03/10] kgdb: delay roundup if holding printk cpulock John Ogness
2021-08-03 14:25   ` Daniel Thompson
2021-08-03 15:30     ` John Ogness
2021-08-04 11:31       ` Daniel Thompson
2021-08-04 12:12         ` Petr Mladek
2021-08-04 15:04           ` Daniel Thompson
2021-08-05  3:46             ` John Ogness
2021-08-06 12:06               ` Daniel Thompson
2021-08-04 12:31       ` Petr Mladek
2021-08-03 13:12 ` [PATCH printk v1 04/10] printk: relocate printk_delay() John Ogness
2021-08-04 13:07   ` Petr Mladek
2021-08-03 13:12 ` [PATCH printk v1 05/10] printk: call boot_delay_msec() in printk_delay() John Ogness
2021-08-04 13:09   ` Petr Mladek
2021-08-31  1:04   ` Sergey Senozhatsky
2021-08-03 13:12 ` [PATCH printk v1 06/10] printk: use seqcount_latch for console_seq John Ogness
2021-08-05 12:16   ` Petr Mladek
2021-08-05 15:26     ` John Ogness
2021-08-06 15:56       ` Petr Mladek
2021-08-31  3:05         ` Sergey Senozhatsky
2021-08-03 13:12 ` [PATCH printk v1 07/10] console: add write_atomic interface John Ogness
2021-08-03 14:02   ` Andy Shevchenko
2021-08-06 10:56     ` John Ogness
2021-08-06 11:18       ` Andy Shevchenko
2021-08-31  2:55   ` Sergey Senozhatsky
2021-08-03 13:12 ` [PATCH printk v1 08/10] printk: introduce kernel sync mode John Ogness
2021-08-05 17:11   ` Petr Mladek
2021-08-05 21:25     ` John Ogness
2021-08-03 13:13 ` [PATCH printk v1 09/10] kdb: if available, only use atomic consoles for output mirroring John Ogness
2021-08-03 13:13 ` [PATCH printk v1 10/10] serial: 8250: implement write_atomic John Ogness
2021-08-03 14:07   ` Andy Shevchenko [this message]
2021-08-05  7:47     ` Jiri Slaby
2021-08-05  8:26       ` John Ogness
2021-08-03 13:52 ` [PATCH printk v1 00/10] printk: introduce atomic consoles and sync mode Andy Shevchenko
2021-08-05 15:47 ` Petr Mladek
2021-08-31  0:33   ` Sergey Senozhatsky

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=YQlNtr7TNAWtB8XF@smile.fi.intel.com \
    --to=andriy.shevchenko@linux.intel.com \
    --cc=Sergey.Semin@baikalelectronics.ru \
    --cc=aabyzov@slb.com \
    --cc=alcooperx@gmail.com \
    --cc=andrew@aj.id.au \
    --cc=christophe.jaillet@wanadoo.fr \
    --cc=eddie.huang@mediatek.com \
    --cc=gregkh@linuxfoundation.org \
    --cc=gustavoars@kernel.org \
    --cc=hsinyi@chromium.org \
    --cc=jirislaby@kernel.org \
    --cc=johan@kernel.org \
    --cc=john.ogness@linutronix.de \
    --cc=kuldip.dwivedi@puresoftware.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mediatek@lists.infradead.org \
    --cc=linux-mips@vger.kernel.org \
    --cc=linux-serial@vger.kernel.org \
    --cc=linux@roeck-us.net \
    --cc=macro@orcam.me.uk \
    --cc=matthias.bgg@gmail.com \
    --cc=paul@crapouillou.net \
    --cc=pmladek@suse.com \
    --cc=rostedt@goodmis.org \
    --cc=senozhatsky@chromium.org \
    --cc=sergey.senozhatsky@gmail.com \
    --cc=tglx@linutronix.de \
    --cc=tientzu@chromium.org \
    --cc=wangqing@vivo.com \
    --cc=zhangqilong3@huawei.com \
    --subject='Re: [PATCH printk v1 10/10] serial: 8250: implement write_atomic' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).