linux-kernel - Re: Major 2.6.38 / 2.6.39 / 3.0 regression ignored?

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Date:	Fri, 22 Jul 2011 11:00:41 -0700
From:	Keith Packard <keithp@...thp.com>
To:	Kirill Smelkov <kirr@....spb.ru>, Pekka Enberg <penberg@...nel.org>
Cc:	Chris Wilson <chris@...is-wilson.co.uk>, Luke-Jr <luke@...hjr.org>,
	intel-gfx@...ts.freedesktop.org,
	LKML <linux-kernel@...r.kernel.org>,
	dri-devel@...ts.freedesktop.org, "Rafael J. Wysocki" <rjw@...k.pl>,
	Ray Lee <ray-lk@...rabbit.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Florian Mickler <florian@...kler.org>
Subject: Re: Major 2.6.38 / 2.6.39 / 3.0 regression ignored?

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.

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);
-- 
1.7.5.4

-- 
keith.packard@...el.com

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