From mboxrd@z Thu Jan  1 00:00:00 1970
From: alexander.stein@systec-electronic.com (Alexander Stein)
Date: Thu, 11 Nov 2010 13:44:54 +0100
Subject: [AT91SAM9260] kernel hang in at91sam926x_pit_reset()
In-Reply-To: <AANLkTik1P9CNYu93ZDc3PU6e=17O8XBg=DdPo1a9VW6c@mail.gmail.com>
References: <AANLkTik1P9CNYu93ZDc3PU6e=17O8XBg=DdPo1a9VW6c@mail.gmail.com>
Message-ID: <201011111345.42080.alexander.stein@systec-electronic.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Thursday 11 November 2010, 12:41:48 Vitja Makarov wrote:
> Hi!
> 
> I've recently found that our new AT91SAM9260 boards does not work with
> linux out of the box.
> The only thing changed is CPU revision now it is "Rev. B' (old boards
> used "Rev. A" CPUs)
> 
> 
> So after uncompressing kernel it writes. "Booting kernel..." that's
> all. Kernel hangs.
> 
> I found that it hangs in  at91sam926x_time.c:at91sam926x_pit_reset():
> 
> Bit in AT91_PIT_PIVR register never clears... so I add timeout for
> this loop and kernel boots as expected.
> 
> static void at91sam926x_pit_reset(void)
> {
> <------>/* Disable timer and irqs */
> <------>at91_sys_write(AT91_PIT_MR, 0);
> 
> <------>/* Clear any pending interrupts, wait for PIT to stop counting */
> <------>while (PIT_CPIV(at91_sys_read(AT91_PIT_PIVR)) != 0)
> <------><------>cpu_relax();
> 
> <------>/* Start PIT but don't enable IRQ */
> <------>at91_sys_write(AT91_PIT_MR, (pit_cycle - 1) | AT91_PIT_PITEN);
> }

This won't work as you cannot set PIT_PITEN until the PIT has stopped 
(UserManuel 17.3), read as CPIV is 0. You should check if and why CPIV isn't 
increasing.

Best regards
Alexander