From mboxrd@z Thu Jan  1 00:00:00 1970
From: Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>
Subject: Re: [PATCH URGENT] arm: dma-mapping: Set DMA IOMMU ops in
	arm_iommu_attach_device()
Date: Fri, 23 Jan 2015 18:00:45 +0100
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To: Laurent Pinchart <laurent.pinchart-ryLnwIuWjnjg/C1BVhZhaw@public.gmane.org>
Cc: jroedel-l3A5Bk7waGM@public.gmane.org, Heiko Stuebner <heiko-4mtYJXux2i+zQB+pC5nmwQ@public.gmane.org>, Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>, iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, Laurent Pinchart <laurent.pinchart+renesas-ryLnwIuWjnjg/C1BVhZhaw@public.gmane.org>, Thierry Reding <thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Varun.Sethi-KZfg59tc24xl57MIdRCFDg@public.gmane.org, Alexandre Courbot <acourbot-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>, dwmw2-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org
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On Friday 23 January 2015 17:55:25 Laurent Pinchart wrote:
> 
> On Friday 23 January 2015 16:27:24 Arnd Bergmann wrote:
> > On Friday 23 January 2015 16:21:49 Laurent Pinchart wrote:
> > > +/**
> > > + * arm_iommu_detach_device
> > > + * @dev: valid struct device pointer
> > > + *
> > > + * Detaches the provided device from a previously attached map.
> > > + * This voids the dma operations (dma_map_ops pointer)
> > > + */
> > > +void arm_iommu_detach_device(struct device *dev)
> > > +{
> > > +       __arm_iommu_detach_device(dev);
> > > +       set_dma_ops(dev, NULL);
> > > +}
> > > 
> > >  EXPORT_SYMBOL_GPL(arm_iommu_detach_device);
> > 
> > Would this introduce a regression in the case where the device is
> > cache coherent and needs arm_coherent_dma_ops set?
> 
> I think we need to handle that case (as well as the coherent IOMMU case in 
> arm_iommu_attach_device), but this patch only tries to restore the previous 
> behaviour to fix the bug detailed in the commit message. Would you prefer 
> fixing both issues in one go ?
> 

No, I was specifically trying to find out whether the new behavior would
be worse than what we had in 3.18. If it's a preexisting bug that nobody
has run into, there is no hurry.

It's quite likely that to date, all IOMMU users on ARM32 are not
cache coherent.

	Arnd