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

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Date:	Wed, 18 Nov 2009 23:49:28 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Wan ZongShun <mcuos.com@...il.com>
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

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()?

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.

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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