linux-kernel - Re: [PATCH 09/14] tty/serial/amba-pl011: Implement clear

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Date:	Mon, 10 Sep 2012 12:17:02 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Anton Vorontsov <anton.vorontsov@...aro.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Russell King <linux@....linux.org.uk>,
	Jason Wessel <jason.wessel@...driver.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alan Cox <alan@...ux.intel.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Colin Cross <ccross@...roid.com>,
	Brian Swetland <swetland@...gle.com>,
	John Stultz <john.stultz@...aro.org>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	kernel-team@...roid.com, kgdb-bugreport@...ts.sourceforge.net,
	linux-serial@...r.kernel.org
Subject: Re: [PATCH 09/14] tty/serial/amba-pl011: Implement clear_irqs
 callback

On Sun, 9 Sep 2012 21:14:04 -0700
Anton Vorontsov <anton.vorontsov@...aro.org> wrote:

> It's all pretty straightforward, except for TXIM interrupt. The interrupt
> has meaning "ready to transmit", so it's almost always raised, and the
> only way to silence it is to mask it. But that's OK, ops->start_tx will
> unmask it.
> 
> Signed-off-by: Anton Vorontsov <anton.vorontsov@...aro.org>
> ---
>  drivers/tty/serial/amba-pl011.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
> index 88e2df2..7522d97 100644
> --- a/drivers/tty/serial/amba-pl011.c
> +++ b/drivers/tty/serial/amba-pl011.c
> @@ -1308,6 +1308,18 @@ static void pl011_put_poll_char(struct uart_port *port,
>  	writew(ch, uap->port.membase + UART01x_DR);
>  }
>  
> +static void pl011_clear_irqs(struct uart_port *port)
> +{
> +	struct uart_amba_port *uap = (struct uart_amba_port *)port;
> +	unsigned char __iomem *regs = uap->port.membase;
> +
> +	writew(readw(regs + UART011_MIS), regs + UART011_ICR);
> +	/*
> +	 * There is no way to clear TXIM, this is "ready to transmit IRQ", so
> +	 * we simply mask it. ops->start_tx will unmask it.
> +	 */

Not if you race here with the transmit start it won't.
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