linux-kernel - Re: [PATCH 02/16] tty: serial: 8250

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Message-ID: <20140929094620.GE13952@ci00147.xsens-tech.local>
Date:	Mon, 29 Sep 2014 11:46:20 +0200
From:	Frans Klaver <frans.klaver@...ns.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
CC:	<linux-serial@...r.kernel.org>, <tony@...mide.com>,
	<gregkh@...uxfoundation.org>, <linux-kernel@...r.kernel.org>,
	<balbi@...com>, <linux-omap@...r.kernel.org>,
	<mika.westerberg@...ux.intel.com>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 02/16] tty: serial: 8250_core: add run time pm

On Wed, Sep 10, 2014 at 09:29:57PM +0200, Sebastian Andrzej Siewior wrote:
> +/*
> + * This two wrapper ensure, that enable_runtime_pm_tx() can be called more than

These two wrappers ensure that enable_runtime_pm_tx() ...

> + * once and disable_runtime_pm_tx() will still disable RPM because the fifo is
> + * empty and the HW can idle again.
> + */
> +static void serial8250_rpm_get_tx(struct uart_8250_port *p)
> +{
> +	unsigned char rpm_active;
> +
> +	if (!(p->capabilities & UART_CAP_RPM))
> +		return;
> +
> +	rpm_active = xchg(&p->rpm_tx_active, 1);
> +	if (rpm_active)
> +		return;
> +	pm_runtime_get_sync(p->port.dev);
> +}
> +
> +static void serial8250_rpm_put_tx(struct uart_8250_port *p)
> +{
> +	unsigned char rpm_active;
> +
> +	if (!(p->capabilities & UART_CAP_RPM))
> +		return;
> +
> +	rpm_active = xchg(&p->rpm_tx_active, 0);
> +	if (!rpm_active)
> +		return;
> +	pm_runtime_mark_last_busy(p->port.dev);
> +	pm_runtime_put_autosuspend(p->port.dev);
> +}
> +


> @@ -1469,7 +1531,12 @@ void serial8250_tx_chars(struct uart_8250_port *up)
>  
>  	DEBUG_INTR("THRE...");
>  
> -	if (uart_circ_empty(xmit))
> +	/*
> +	 * With RPM enabled, we have to wait once the FIFO is empty before the

s,once,until,? Or do I not understand the sentence correctly?

> +	 * HW can go idle. So we get here once again with empty FIFO and disable
> +	 * the interrupt and RPM in __stop_tx()
> +	 */
> +	if (uart_circ_empty(xmit) && !(up->capabilities & UART_CAP_RPM))
>  		__stop_tx(up);
>  }
>  EXPORT_SYMBOL_GPL(serial8250_tx_chars);
--
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