linux-kernel - Re: [PATCH] Clear previous interrupts after fifo is disabled

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Date:	Mon, 27 Feb 2012 11:45:12 +0100
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Chanho Min <chanho0207@...il.com>
Cc:	Russell King <linux@....linux.org.uk>,
	Alan Cox <alan@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Shreshtha Kumar Sahu <shreshthakumar.sahu@...ricsson.com>,
	"Kim, Jong-Sung" <neidhard.kim@....com>,
	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH] Clear previous interrupts after fifo is disabled

On Mon, Feb 27, 2012 at 10:30 AM, Chanho Min <chanho0207@...il.com> wrote:

> This is another workaroud of  'https://lkml.org/lkml/2012/1/17/104'
> with additional analysis.Bootloader can transfer control to kernel and
> there are some pending interrupts. In this case, RXFE of the flag
> register is set by clearing FEN(LCRH) even if rx data remains in the
> fifo. It seems that the fifo's status is initiailized. Interrupt
> handler can not get any data from data register because of the below
> break condtion.
>
> pl011_fifo_to_tty
>  while (max_count--) {
>   if (status & UART01x_FR_RXFE)
>        break;
>
> Then, Rx interrupt is never cleared. cpu is looping in ISR. System is
> hang. If we don't guarantee that no interrupt is pended until fifo is
> disabled by calling 'writew(0, uap->port.membase + uap->lcrh_rx)',
> this misbehave of the interrupt handelr can be occurred. So, All
> pending interrupts should be cleared just after fifo is disabled under
> the protection from interrupt. Also,'clear error interrupts' routine
> can be removed becuase all interrupts are cleared before.
>
> Signed-off-by: Chanho Min <chanho.min@....com>

Looks correct to me.
Acked-by: Linus Walleij <linus.walleij@...aro.org>

Thanks,
Linus Walleij
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