linux-kernel - Re: [PATCH] synchronize

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Date:	Sat, 20 Oct 2007 08:06:41 +0200
From:	Maxim Levitsky <maximlevitsky@...il.com>
To:	benh@...nel.crashing.org
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	akpm <akpm@...ux-foundation.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	linuxppc-dev list <linuxppc-dev@...abs.org>
Subject: Re: [PATCH] synchronize_irq needs a barrier

On Saturday 20 October 2007 07:46:24 Benjamin Herrenschmidt wrote:
> 
> > I probably need to add this synchronize_irq() logic in dmfe.c too, but I probably do it later,
> > I think I am overestimating this race, since most drivers don't do dev->insuspend checks in IRQ handler.
> > Maybe even just use free_irq() after all....
> 
> Most drivers are probably underestimating the race :-)
> 
> free_irq() would work provided that you did the masking on chip before
> (and unmask only after request_irq on the way back in). But it's a bit
> like using a 10 tons truck to crush an ant... 
Agreed.

So, I will add synchronize_irq() to both saa7134, and dmfe, the two drivers that their .suspend/.resume 
routines were written by me.

I already added a synchronize_irq()  plus few more fixes to the driver , but those patches are still in v4l tree.

I now has this:

	saa_writel(SAA7134_IRQ1, 0);
	saa_writel(SAA7134_IRQ2, 0);
	saa_writel(SAA7134_MAIN_CTRL, 0);

	synchronize_irq(pci_dev->irq);
	dev->insuspend = 1;

and I will probably need (with the synchronize_irq patch applied)


	/* Disable interrupts, DMA, and rest of the chip*/
	saa_writel(SAA7134_IRQ1, 0);
	saa_writel(SAA7134_IRQ2, 0);
	saa_writel(SAA7134_MAIN_CTRL, 0);
	
	dev->insuspend = 1;
	synchronize_irq(pci_dev->irq);

	/* ACK pending interrupts just in case*/
	saa_writel(SAA7134_IRQ_REPORT,saa_readl(SAA7134_IRQ_REPORT));

	......
This should be bullet-proof.


> 
> Ben.
> 
> 
> 
Best regards,
	Maxim Levitsky
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