Re: [PATCH v4] drm/i915: stop using swiotlb
From: Robert Beckett
Date: Tue Jul 26 2022 - 10:25:13 EST
On 26/07/2022 14:12, Tvrtko Ursulin wrote:
On 25/07/2022 15:18, Robert Beckett wrote:
Calling swiotlb functions directly is nowadays considered harmful. See
https://lore.kernel.org/intel-gfx/20220711082614.GA29487@xxxxxx/
Replace swiotlb_max_segment() calls with dma_max_mapping_size().
In i915_gem_object_get_pages_internal() no longer consider max_segment
only if CONFIG_SWIOTLB is enabled. There can be other (iommu related)
causes of specific max segment sizes.
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
Cc: Thomas Hellstrom <thomas.hellstrom@xxxxxxxxx>
Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
v2: - restore UINT_MAX clamp in i915_sg_segment_size()
- drop PAGE_SIZE check as it will always be >= PAGE_SIZE
v3: - actually clamp to UINT_MAX in i915_sg_segment_size()
v4: - round down max segment size to PAGE_SIZE
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Signed-off-by: Robert Beckett <bob.beckett@xxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/gem/i915_gem_internal.c | 19 ++++---------------
drivers/gpu/drm/i915/gem/i915_gem_shmem.c | 2 +-
drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 4 ++--
drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 2 +-
drivers/gpu/drm/i915/i915_scatterlist.h | 17 ++++-------------
5 files changed, 12 insertions(+), 32 deletions(-)
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_internal.c
b/drivers/gpu/drm/i915/gem/i915_gem_internal.c
index c698f95af15f..24f37658f1bb 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_internal.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_internal.c
@@ -6,7 +6,6 @@
#include <linux/scatterlist.h>
#include <linux/slab.h>
-#include <linux/swiotlb.h>
#include "i915_drv.h"
#include "i915_gem.h"
@@ -38,22 +37,12 @@ static int
i915_gem_object_get_pages_internal(struct drm_i915_gem_object *obj)
struct scatterlist *sg;
unsigned int sg_page_sizes;
unsigned int npages;
- int max_order;
+ int max_order = MAX_ORDER;
+ unsigned int max_segment;
gfp_t gfp;
- max_order = MAX_ORDER;
-#ifdef CONFIG_SWIOTLB
- if (is_swiotlb_active(obj->base.dev->dev)) {
- unsigned int max_segment;
-
- max_segment = swiotlb_max_segment();
- if (max_segment) {
- max_segment = max_t(unsigned int, max_segment,
- PAGE_SIZE) >> PAGE_SHIFT;
- max_order = min(max_order, ilog2(max_segment));
- }
- }
-#endif
+ max_segment = i915_sg_segment_size(i915->drm.dev) >> PAGE_SHIFT;
+ max_order = min(max_order, ilog2(max_segment));
gfp = GFP_KERNEL | __GFP_HIGHMEM | __GFP_RECLAIMABLE;
if (IS_I965GM(i915) || IS_I965G(i915)) {
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
index 4eed3dd90ba8..34b9c76cd8e6 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
@@ -194,7 +194,7 @@ static int shmem_get_pages(struct
drm_i915_gem_object *obj)
struct intel_memory_region *mem = obj->mm.region;
struct address_space *mapping = obj->base.filp->f_mapping;
const unsigned long page_count = obj->base.size / PAGE_SIZE;
- unsigned int max_segment = i915_sg_segment_size();
+ unsigned int max_segment = i915_sg_segment_size(i915->drm.dev);
struct sg_table *st;
struct sgt_iter sgt_iter;
struct page *page;
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
index 5a5cf332d8a5..7a828c9c0f6d 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
@@ -189,7 +189,7 @@ static int i915_ttm_tt_shmem_populate(struct
ttm_device *bdev,
struct drm_i915_private *i915 = container_of(bdev,
typeof(*i915), bdev);
struct intel_memory_region *mr =
i915->mm.regions[INTEL_MEMORY_SYSTEM];
struct i915_ttm_tt *i915_tt = container_of(ttm,
typeof(*i915_tt), ttm);
- const unsigned int max_segment = i915_sg_segment_size();
+ const unsigned int max_segment =
i915_sg_segment_size(i915->drm.dev);
const size_t size = (size_t)ttm->num_pages << PAGE_SHIFT;
struct file *filp = i915_tt->filp;
struct sgt_iter sgt_iter;
@@ -568,7 +568,7 @@ static struct i915_refct_sgt
*i915_ttm_tt_get_st(struct ttm_tt *ttm)
ret = sg_alloc_table_from_pages_segment(st,
ttm->pages, ttm->num_pages,
0, (unsigned long)ttm->num_pages << PAGE_SHIFT,
- i915_sg_segment_size(), GFP_KERNEL);
+ i915_sg_segment_size(i915_tt->dev), GFP_KERNEL);
if (ret) {
st->sgl = NULL;
return ERR_PTR(ret);
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
index 094f06b4ce33..dfc35905dba2 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
@@ -129,7 +129,7 @@ static void
i915_gem_object_userptr_drop_ref(struct drm_i915_gem_object *obj)
static int i915_gem_userptr_get_pages(struct drm_i915_gem_object *obj)
{
const unsigned long num_pages = obj->base.size >> PAGE_SHIFT;
- unsigned int max_segment = i915_sg_segment_size();
+ unsigned int max_segment = i915_sg_segment_size(obj->base.dev->dev);
struct sg_table *st;
unsigned int sg_page_sizes;
struct page **pvec;
diff --git a/drivers/gpu/drm/i915/i915_scatterlist.h
b/drivers/gpu/drm/i915/i915_scatterlist.h
index 9ddb3e743a3e..1377a97a20cf 100644
--- a/drivers/gpu/drm/i915/i915_scatterlist.h
+++ b/drivers/gpu/drm/i915/i915_scatterlist.h
@@ -9,7 +9,7 @@
#include <linux/pfn.h>
#include <linux/scatterlist.h>
-#include <linux/swiotlb.h>
+#include <linux/dma-mapping.h>
#include "i915_gem.h"
@@ -127,19 +127,10 @@ static inline unsigned int
i915_sg_dma_sizes(struct scatterlist *sg)
return page_sizes;
}
-static inline unsigned int i915_sg_segment_size(void)
+static inline unsigned int i915_sg_segment_size(struct device *dev)
{
- unsigned int size = swiotlb_max_segment();
-
- if (size == 0)
- size = UINT_MAX;
-
- size = rounddown(size, PAGE_SIZE);
- /* swiotlb_max_segment_size can return 1 byte when it means one
page. */
- if (size < PAGE_SIZE)
- size = PAGE_SIZE;
-
- return size;
+ size_t max = min_t(size_t, UINT_MAX, dma_max_mapping_size(dev));
Hope your patience is not growing thin but blank line here as per
checkpatch. I could fudge when applying though.
no worries, I'll issue a new version shortly.
I only recently guided a mentee to "always do your checkpatch, even if
only doing a quick 1 character change, you never know if it you make a
small mistake"
I guess do as I say, not as I do applies here :)
Otherwise it finally passed CI, yay! Now do we dig deeper to a)
understand how/where it failed and b) check what are the possible return
values from dma_max_mapping_size(), or call it done?
I will have to call it done myself as I am unable to repo it locally.
I could spend a lot of time debugging it via trybot, but I expect it
will be easier, quicker and cheaper to get someone with local hw with a
repro case to debug it if you want to root cause it.
Regards,
Tvrtko
+ return round_down(max, PAGE_SIZE);
}
bool i915_sg_trim(struct sg_table *orig_st);