linux-kernel - Re: [PATCH] ARM: Add spi controller driver support for NUC900

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Message-ID: <e68bb3470911190149k3bc77ef6h26475bc7272784b8@mail.gmail.com>
Date:	Thu, 19 Nov 2009 17:49:22 +0800
From:	Wan ZongShun <mcuos.com@...il.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-spi <spi-devel-general@...ts.sourceforge.net>,
	David Brownell-sourceforge <dbrownell@...rs.sourceforge.net>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] ARM: Add spi controller driver support for NUC900

2009/11/19 Russell King - ARM Linux <linux@....linux.org.uk>:
> On Thu, Nov 19, 2009 at 04:40:50PM +0800, Wan ZongShun wrote:
>> 2009/11/19 Andrew Morton <akpm@...ux-foundation.org>:
>> > I don't know, because I don't know what operation the hardware needs to
>> > stop it from generating interrupts.  Perhaps that's clk_disable()?
>>
>> The interrupt will be not occur as long as I run clk_disable().
>>
>> > Once you've stopped the source of interrupts then the code should wait
>> > for the IRQ handler to complete if it's running on another CPU.  Yes,
>> > free_irq() does that.
>>
>> So, regarding my system of single CPU, maybe I need put this
>> 'clk_disable()' in the front of function of w90p910_spi_remove().
>>
>> right?
>
> Depending on the hardware, that's not the right answer.  If turning off
> the clock also causes register accesses to the device to abort, it is
> a very dangerous thing to do.
>
> It can also be dangerous if the clock is used to synchronise the interrupt
> output - it can lead to the output being permanently asserted if the clock
> is turned off with it asserted.
>
> Normally devices have an "interrupt enable" register.  You should disable
> all interrupts from the device using this register after unregistering
> the driver from the (SPI) subsystem.

sir, so I need implement a API to disable spi device interrupt by
"interrupt enable" register?
but I did not find the operation in other ARM platform when they close
your spi driver.

or something I missed?

>

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