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

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Date:	Thu, 19 Nov 2009 16:40:50 +0800
From:	Wan ZongShun <mcuos.com@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-spi <spi-devel-general@...ts.sourceforge.net>,
	David Brownell-sourceforge <dbrownell@...rs.sourceforge.net>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: Add spi controller driver support for NUC900

2009/11/19 Andrew Morton <akpm@...ux-foundation.org>:
> On Thu, 19 Nov 2009 14:23:49 +0800 Wan ZongShun <mcuos.com@...il.com> wrote:
>
>> >> +static int __devexit w90p910_spi_remove(struct platform_device *dev)
>> >> +{
>> >> + __ __ struct w90p910_spi *hw = platform_get_drvdata(dev);
>> >> +
>> >> + __ __ platform_set_drvdata(dev, NULL);
>> >> +
>> >> + __ __ spi_unregister_master(hw->master);
>> >> +
>> >> + __ __ clk_disable(hw->clk);
>> >> + __ __ clk_put(hw->clk);
>> >
>> > As far as I can tell, a hardware interrupt could still be pending, or
>> > be under service while the above code is executing?
>> >
>> > If so, I expect bad things will happen?
>>
>> Do you mean that I should put this 'free_irq()' in the front of
>> w90p910_spi_remove___
>>
>> such as:
>> "
>> free_irq(hw->irq, hw);
>>
>> platform_set_drvdata(dev, NULL);
>>
>> spi_unregister_master(hw->master);
>>
>> clk_disable(hw->clk);
>> clk_put(hw->clk);
>
> 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?

> It's only after the clk_disable() and the free_irq() that you can
> guarantee that no interrupt handler will run and attempt to access the
> device and its associated data structures.
>
>

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