Re: [PATCH RFC 2/4] drm/i915: IOMMU based SVM implementation v13

From: David Woodhouse <dwmw2@infradead.org>
To: Chris Wilson <chris@chris-wilson.co.uk>,
	Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>,
	intel-gfx@lists.freedesktop.org,
	Jesse Barnes <jbarnes@virtuousgeek.org>
Subject: Re: [PATCH RFC 2/4] drm/i915: IOMMU based SVM implementation v13
Date: Mon, 15 Aug 2016 13:13:25 +0100	[thread overview]
Message-ID: <1471263205.61594.219.camel@infradead.org> (raw)
In-Reply-To: <20160815120557.GD29357@nuc-i3427.alporthouse.com>

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On Mon, 2016-08-15 at 13:05 +0100, Chris Wilson wrote:
> On Mon, Aug 15, 2016 at 02:48:05PM +0300, Mika Kuoppala wrote:
> > 
> > +	struct task_struct *task;
> 
> We don't need the task, we need the mm.
> 
> Holding the task is not sufficient.

From the pure DMA point of view, you don't need the MM at all. I handle
all that from the IOMMU side so it's none of your business, darling.

However, if you want to relate a given context to the specific thread
which started it, perhaps to deliver signals or whatever else, then
perhaps you do want the task not the MM.

> 
> > --- a/drivers/gpu/drm/i915/i915_gem.c
> > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > @@ -4304,6 +4304,13 @@ i915_gem_init_hw(struct drm_device *dev)
> >  		}
> >  	}
> >  
> > +	if (INTEL_GEN(dev) >= 8) {
> > +		if (intel_init_svm(dev))
> 
> init_hw ?
> 
> This looks more like one off early driver init.

It's a per-device thing. You might support SVM on one device but not
another, depending on how the IOMMU is configured. Note the 'dev'
argument in the call to intel_init_svm().

-- 
dwmw2

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