Message-Id: <201108091903.00071.anarsoul@gmail.com>
Date:	Tue, 9 Aug 2011 19:02:59 +0300
From:	Vasily Khoruzhick <anarsoul@...il.com>
To:	Kirill Smelkov <kirr@....spb.ru>
Cc:	intel-gfx@...ts.freedesktop.org, Keith Packard <keithp@...thp.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"Luke-Jr" <luke@...hjr.org>, LKML <linux-kernel@...r.kernel.org>,
	dri-devel@...ts.freedesktop.org, Pekka Enberg <penberg@...nel.org>,
	Ray Lee <ray-lk@...rabbit.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [Intel-gfx] Major 2.6.38 / 2.6.39 / 3.0 regression ignored?

On Tuesday 09 August 2011 18:34:46 Kirill Smelkov wrote:
> On Tue, Aug 09, 2011 at 06:09:57PM +0300, Vasily Khoruzhick wrote:
> > On Tuesday 09 August 2011 17:47:56 Kirill Smelkov wrote:
> > > On Tue, Aug 09, 2011 at 05:00:52PM +0300, Vasily Khoruzhick wrote:
> > > > On Tuesday 09 August 2011 15:08:03 Kirill Smelkov wrote:
> > > > > On Tue, Jul 26, 2011 at 05:48:27PM +0400, Kirill Smelkov wrote:
> > > > > > On Sat, Jul 23, 2011 at 12:23:36AM +0400, Kirill Smelkov wrote:
> > > > > > > Keith,
> > > > > > > 
> > > > > > > first of all thanks for your prompt reply. Then...
> > > > > > > 
> > > > > > > On Fri, Jul 22, 2011 at 11:00:41AM -0700, Keith Packard wrote:
> > > > > > > > On Fri, 22 Jul 2011 15:08:06 +0400, Kirill Smelkov
> > > > > > > > <kirr@....spb.ru>
> > > > 
> > > > wrote:
> > > > > > > > > And now after v3.0 is out, I've tested it again, and yes,
> > > > > > > > > like it was broken on v3.0-rc5, it is (now even more)
> > > > > > > > > broken on v3.0 -- after first
> > > > > > > > 
> > > > > > > > > bad io access the system freezes completely:
> > > > > > > > I looked at this when I first saw it (a couple of weeks ago),
> > > > > > > > and I couldn't see any obvious reason this patch would cause
> > > > > > > > this particular problem. I didn't want to revert the patch
> > > > > > > > at that point as I feared it would cause other subtle
> > > > > > > > problems. Given that you've got a work-around, it seemed
> > > > > > > > best to just push this off past 3.0.
> > > > > > > 
> > > > > > > What kind of a workaround are you talking about? Sorry, to me
> > > > > > > it all looked like "UMS is being ignored forever". Anyway,
> > > > > > > let's move on to try to solve the issue.
> > > > > > > 
> > > > > > > > Given the failing address passed to ioread32, this seems like
> > > > > > > > it's probably the call to READ_BREADCRUMB --
> > > > > > > > I915_BREADCRUMB_INDEX is 0x21, which is an offset in 32-bit
> > > > > > > > units within the hardware status page. If the
> > > > > > > > status_page.page_addr value was zero, then the computed
> > > > > > > > address would end up being 0x84.
> > > > > > > > 
> > > > > > > > And, it looks like status_page.page_addr *will* end up being
> > > > > > > > zero as a result of the patch in question. The patch resets
> > > > > > > > the entire ring structure contents back to the initial
> > > > > > > > values, which includes smashing the status_page structure to
> > > > > > > > zero, clearing the value of status_page.page_addr set in
> > > > > > > > i915_init_phys_hws.
> > > > > > > > 
> > > > > > > > Here's an untested patch which moves the initialization of
> > > > > > > > status_page.page_addr into intel_render_ring_init_dri. I note
> > > > > > > > that intel_init_render_ring_buffer *already* has the setting
> > > > > > > > of the status_page.page_addr value, and so I've removed the
> > > > > > > > setting of status_page.page_addr from i915_init_phys_hws.
> > > > > > > > 
> > > > > > > > I suspect we could remove the memset from
> > > > > > > > intel_init_render_ring_buffer; it seems entirely superfluous
> > > > > > > > given the memset in i915_init_phys_hws.
> > > > > > > > 
> > > > > > > > From 159ba1dd207fc52590ce8a3afd83f40bd2cedf46 Mon Sep 17
> > > > > > > > 00:00:00 2001 From: Keith Packard <keithp@...thp.com>
> > > > > > > > Date: Fri, 22 Jul 2011 10:44:39 -0700
> > > > > > > > Subject: [PATCH] drm/i915: Initialize RCS ring status page
> > > > > > > > address in
> > > > > > > > 
> > > > > > > >  intel_render_ring_init_dri
> > > > > > > > 
> > > > > > > > Physically-addressed hardware status pages are initialized
> > > > > > > > early in the driver load process by i915_init_phys_hws. For
> > > > > > > > UMS environments, the ring structure is not initialized
> > > > > > > > until the X server starts. At that point, the entire ring
> > > > > > > > structure is re-initialized with all new values. Any values
> > > > > > > > set in the ring structure (including
> > > > > > > > ring->status_page.page_addr) will be lost when the ring is
> > > > > > > > re-initialized.
> > > > > > > > 
> > > > > > > > This patch moves the initialization of the
> > > > > > > > status_page.page_addr value to intel_render_ring_init_dri.
> > > > > > > > 
> > > > > > > > Signed-off-by: Keith Packard <keithp@...thp.com>
> > > > > > > > ---
> > > > > > > > 
> > > > > > > >  drivers/gpu/drm/i915/i915_dma.c         |    6 ++----
> > > > > > > >  drivers/gpu/drm/i915/intel_ringbuffer.c |    3 +++
> > > > > > > >  2 files changed, 5 insertions(+), 4 deletions(-)
> > > > > > > > 
> > > > > > > > diff --git a/drivers/gpu/drm/i915/i915_dma.c
> > > > > > > > b/drivers/gpu/drm/i915/i915_dma.c index 1271282..8a3942c
> > > > > > > > 100644 --- a/drivers/gpu/drm/i915/i915_dma.c
> > > > > > > > +++ b/drivers/gpu/drm/i915/i915_dma.c
> > > > > > > > @@ -61,7 +61,6 @@ static void i915_write_hws_pga(struct
> > > > > > > > drm_device *dev)
> > > > > > > > 
> > > > > > > >  static int i915_init_phys_hws(struct drm_device *dev)
> > > > > > > >  {
> > > > > > > >  
> > > > > > > >  	drm_i915_private_t *dev_priv = dev->dev_private;
> > > > > > > > 
> > > > > > > > -	struct intel_ring_buffer *ring = LP_RING(dev_priv);
> > > > > > > > 
> > > > > > > >  	/* Program Hardware Status Page */
> > > > > > > >  	dev_priv->status_page_dmah =
> > > > > > > > 
> > > > > > > > @@ -71,10 +70,9 @@ static int i915_init_phys_hws(struct
> > > > > > > > drm_device *dev)
> > > > > > > > 
> > > > > > > >  		DRM_ERROR("Can not allocate hardware status page\n");
> > > > > > > >  		return -ENOMEM;
> > > > > > > >  	
> > > > > > > >  	}
> > > > > > > > 
> > > > > > > > -	ring->status_page.page_addr =
> > > > > > > > -		(void __force __iomem *)dev_priv->status_page_dmah-
>vaddr;
> > > > > > > > 
> > > > > > > > -	memset_io(ring->status_page.page_addr, 0, PAGE_SIZE);
> > > > > > > > +	memset_io((void __force __iomem
> > > > > > > > *)dev_priv->status_page_dmah->vaddr, +		  0, PAGE_SIZE);
> > > > > > > > 
> > > > > > > >  	i915_write_hws_pga(dev);
> > > > > > > > 
> > > > > > > > diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c
> > > > > > > > b/drivers/gpu/drm/i915/intel_ringbuffer.c index
> > > > > > > > e961568..47b9b27 100644
> > > > > > > > --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> > > > > > > > +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> > > > > > > > @@ -1321,6 +1321,9 @@ int intel_render_ring_init_dri(struct
> > > > > > > > drm_device *dev, u64 start, u32 size)
> > > > > > > > 
> > > > > > > >  		ring->get_seqno = pc_render_get_seqno;
> > > > > > > >  	
> > > > > > > >  	}
> > > > > > > > 
> > > > > > > > +	if (!I915_NEED_GFX_HWS(dev))
> > > > > > > > +		ring->status_page.page_addr =
> > > > > > > > dev_priv->status_page_dmah->vaddr; +
> > > > > > > > 
> > > > > > > >  	ring->dev = dev;
> > > > > > > >  	INIT_LIST_HEAD(&ring->active_list);
> > > > > > > >  	INIT_LIST_HEAD(&ring->request_list);
> > > > > > > 
> > > > > > > I can't tell whether this is correct, because intel gfx driver
> > > > > > > is unknown to me, but from the first glance your description
> > > > > > > sounds reasonable.
> > > > > > > 
> > > > > > > I'm out of office till ~ next week's tuesday, and on return
> > > > > > > I'll try to test it on the hardware in question.
> > > > > > 
> > > > > > Keith, thanks again for the patch. As promised I've tested it on
> > > > > > the hardware in question and yes, bad_access is gone and X seems
> > > > > > to work, so thank you, but...
> > > > > > 
> > > > > > 
> > > > > > I see there are more such bugs in introduced-in-guilty-patch
> > > > > > intel_render_ring_init_dri(). For example ring->irq_queue is
> > > > > > left uninitialized and also ring->irq_lock etc...
> > > > > > 
> > > > > > 
> > > > > > I'm X newbie, so if here is something stupid X-wise, please don't
> > > > > > beat me too hard, but to me the gist of the problem is the
> > > > > > original patch, where Chris does
> > > > > > 
> > > > > > ( git show e8616b6ced6137085e6657cc63bc2fe3900b8616 )
> > > > > > 
> > > > > > > diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c
> > > > > > > b/drivers/gpu/drm/i915/intel_ringbuffer.c index
> > > > > > > 03e3370..51fbc5e 100644
> > > > > > > --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> > > > > > > +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> > > > > > > @@ -1291,6 +1291,48 @@ int intel_init_render_ring_buffer(struct
> > > > > > > drm_device *dev)
> > > > > > > 
> > > > > > >         return intel_init_ring_buffer(dev, ring);
> > > > > > >  
> > > > > > >  }
> > > > > > > 
> > > > > > > +int intel_render_ring_init_dri(struct drm_device *dev, u64
> > > > > > > start, u32 size) +{
> > > > > > > +       drm_i915_private_t *dev_priv = dev->dev_private;
> > > > > > > +       struct intel_ring_buffer *ring = &dev_priv->ring[RCS];
> > > > > > > +
> > > > > > > +       *ring = render_ring;
> > > > > > > 
> > > > > >           ^^^^^^^^^^^^^^^^^^^
> > > > > >           here resets
> > > > > > > 
> > > > > > > +       if (INTEL_INFO(dev)->gen >= 6) {
> > > > > > > +               ring->add_request = gen6_add_request;
> > > > > > > +               ring->irq_get = gen6_render_ring_get_irq;
> > > > > > > +               ring->irq_put = gen6_render_ring_put_irq;
> > > > > > > +       } else if (IS_GEN5(dev)) {
> > > > > > > +               ring->add_request = pc_render_add_request;
> > > > > > > +               ring->get_seqno = pc_render_get_seqno;
> > > > > > > +       }
> > > > > > 
> > > > > > and then the rest of the `ring` is initialized seemingly
> > > > > > copy-pasted
> > > > > > 
> > > > > > from intel_init_ring_buffer():
> > > > > > > +       ring->dev = dev;
> > > > > > > +       INIT_LIST_HEAD(&ring->active_list);
> > > > > > > +       INIT_LIST_HEAD(&ring->request_list);
> > > > > > > +       INIT_LIST_HEAD(&ring->gpu_write_list);
> > > > > > > +
> > > > > > > +       ring->size = size;
> > > > > > > +       ring->effective_size = ring->size;
> > > > > > > +       if (IS_I830(ring->dev))
> > > > > > > +               ring->effective_size -= 128;
> > > > > > > +
> > > > > > > +       ring->map.offset = start;
> > > > > > > +       ring->map.size = size;
> > > > > > > +       ring->map.type = 0;
> > > > > > > +       ring->map.flags = 0;
> > > > > > > +       ring->map.mtrr = 0;
> > > > > > 
> > > > > > ...
> > > > > > 
> > > > > > where both 3 chunks go almost exactly from
> > > > > > intel_init_ring_buffer(), and ring->effective_size tweak even
> > > > > > stripped original comment:
> > > > > > 
> > > > > > # original version from intel_init_ring_buffer():
> > > > > >         /* Workaround an erratum on the i830 which causes a hang
> > > > > >         if
> > > > > >         
> > > > > >          * the TAIL pointer points to within the last 2
> > > > > >          cachelines * of the buffer.
> > > > > >          */
> > > > > >         
> > > > > >         ring->effective_size = ring->size;
> > > > > >         if (IS_I830(ring->dev))
> > > > > >         
> > > > > >                 ring->effective_size -= 128;
> > > > > > 
> > > > > > ...
> > > > > > 
> > > > > > 
> > > > > > The line marked "here resets" resets all the fields, and maybe
> > > > > > it's not a good idea to re-initialize them all afterwards
> > > > > > (missing some as this thread show), or at least if it is really
> > > > > > needed, share initialization code between
> > > > > > intel_render_ring_init_dri() and intel_init_ring_buffer() ?
> > > > > > 
> > > > > > >From the outside it looks like the offending patch was done as a
> > > > > > >quick
> > > > > > 
> > > > > > fix in a hurry (lots of copy-paste), and maybe it would be better
> > > > > > to re-do it properly...
> > > > > 
> > > > > Silence... ?
> > > > > 
> > > > > I read UMS is still ignored, because e.g. that uninitialized
> > > > > ring->irq_lock which I've wrote about above is for sure used e.g.
> > > > > in gen6_render_ring_get_irq() added to ring vtable in
> > > > > intel_render_ring_init_dri().
> > > > 
> > > > I really doubt that UMS supports gen6 hardware.
> > > 
> > > Then why it is there in intel_render_ring_init_dri():
> > >     int intel_render_ring_init_dri(struct drm_device *dev, u64 start,
> > >     u32
> > > 
> > > size) {
> > > 
> > >     	drm_i915_private_t *dev_priv = dev->dev_private;
> > >     	struct intel_ring_buffer *ring = &dev_priv->ring[RCS];
> > >     	
> > >     	*ring = render_ring;
> > >     	if (INTEL_INFO(dev)->gen >= 6) {
> > 
> > This branch executes only when hw generation is 6 or newer.
> 
> and adds gen6_render_ring_get_irq() to vtable which uses ring->irq_lock
> which is left uninitialized.
> 
> I don't understand what you were trying to say. How does it matter if
> some branch executes only for such-and-such hardware, when this branch
> contains bugs? Could you please clarify?

I want to say that xf86-video-intel with gen6 support does not support UMS. So 
you can't even hit this "bug".
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