FAILED: patch "[PATCH] drm/i915: make compact dma scatter lists creation work with" failed to apply to 3.10-stable tree

[gregkh at linuxfoundation.org]

The patch below does not apply to the 3.10-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable at vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From 1625e7e549c50fb57a1e1ab1cb0f5735c84c9029 Mon Sep 17 00:00:00 2001
From: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Date: Mon, 24 Jun 2013 11:47:48 -0400
Subject: [PATCH] drm/i915: make compact dma scatter lists creation work with
 SWIOTLB backend.

Git commit 90797e6d1ec0dfde6ba62a48b9ee3803887d6ed4
("drm/i915: create compact dma scatter lists for gem objects") makes
certain assumptions about the under laying DMA API that are not always
correct.

On a ThinkPad X230 with an Intel HD 4000 with Xen during the bootup
I see:

[drm:intel_pipe_set_base] *ERROR* pin & fence failed
[drm:intel_crtc_set_config] *ERROR* failed to set mode on [CRTC:3], err = -28

Bit of debugging traced it down to dma_map_sg failing (in
i915_gem_gtt_prepare_object) as some of the SG entries were huge (3MB).

That unfortunately are sizes that the SWIOTLB is incapable of handling -
the maximum it can handle is a an entry of 512KB of virtual contiguous
memory for its bounce buffer. (See IO_TLB_SEGSIZE).

Previous to the above mention git commit the SG entries were of 4KB, and
the code introduced by above git commit squashed the CPU contiguous PFNs
in one big virtual address provided to DMA API.

This patch is a simple semi-revert - were we emulate the old behavior
if we detect that SWIOTLB is online. If it is not online then we continue
on with the new compact scatter gather mechanism.

An alternative solution would be for the the '.get_pages' and the
i915_gem_gtt_prepare_object to retry with smaller max gap of the
amount of PFNs that can be combined together - but with this issue
discovered during rc7 that might be too risky.

Reported-and-Tested-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
CC: Chris Wilson <chris at chris-wilson.co.uk>
CC: Imre Deak <imre.deak at intel.com>
CC: Daniel Vetter <daniel.vetter at ffwll.ch>
CC: David Airlie <airlied at linux.ie>
CC: <dri-devel at lists.freedesktop.org>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Cc: stable at vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index a6178bac..e31eeb1d 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1802,7 +1802,14 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
 			gfp |= __GFP_NORETRY | __GFP_NOWARN | __GFP_NO_KSWAPD;
 			gfp &= ~(__GFP_IO | __GFP_WAIT);
 		}
-
+#ifdef CONFIG_SWIOTLB
+		if (swiotlb_nr_tbl()) {
+			st->nents++;
+			sg_set_page(sg, page, PAGE_SIZE, 0);
+			sg = sg_next(sg);
+			continue;
+		}
+#endif
 		if (!i || page_to_pfn(page) != last_pfn + 1) {
 			if (i)
 				sg = sg_next(sg);
@@ -1813,8 +1820,10 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
 		}
 		last_pfn = page_to_pfn(page);
 	}
-
-	sg_mark_end(sg);
+#ifdef CONFIG_SWIOTLB
+	if (!swiotlb_nr_tbl())
+#endif
+		sg_mark_end(sg);
 	obj->pages = st;
 
 	if (i915_gem_object_needs_bit17_swizzle(obj))