Re: Major 2.6.38 / 2.6.39 / 3.0 regression ignored?

From: Keith Packard
Date: Fri Jul 22 2011 - 14:00:56 EST

On Fri, 22 Jul 2011 15:08:06 +0400, Kirill Smelkov <kirr@xxxxxxxxxx> 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@xxxxxxxxxx>
Date: Fri, 22 Jul 2011 10:44:39 -0700
Subject: [PATCH] drm/i915: Initialize RCS ring status page address in

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

This patch moves the initialization of the status_page.page_addr value
to intel_render_ring_init_dri.

Signed-off-by: Keith Packard <keithp@xxxxxxxxxx>
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);


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;


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