Re: [PATCH v5] drm/i915: stop using swiotlb

2022-08-09 Thread Tvrtko Ursulin 



On 08/08/2022 16:48, Hellstrom, Thomas wrote:

Hi, [back from vacation]

On Tue, 2022-07-26 at 16:39 +0100, Robert Beckett wrote:

Calling swiotlb functions directly is nowadays considered harmful.
See
https://lore.kernel.org/intel-gfx/20220711082614.ga29...@lst.de/

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 
Cc: Tvrtko Ursulin 
Cc: Thomas Hellstrom 
Cc: Matthew Auld 

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
v5: - fix checkpatch whitespace issue

Reviewed-by: Christoph Hellwig 
Reviewed-by: Tvrtko Ursulin 
Signed-off-by: Robert Beckett 


Hmm,

This whole thing looks a bit strange to me since with SWIOTLB actually
used for i915, the driver should malfunction anyway as it doesn't do
any dma_sync_sg_for_cpu() or dma_sync_sg_for_device(), and the driver
assumes all coherent dma. Is that SWIOTLB=force kernel option still
available?


Don't know about these - but pretty sure in the past we had i915 break 
if we did not respect swiotlb_max_segment.


Digging through git history at least running as Xen dom0 looks to have 
been impacted, but commits such as abb0deacb5a6 ("drm/i915: Fallback to 
single PAGE_SIZE segments for DMA remapping") are older and suggest 
problem was generic. 1625e7e549c5 ("drm/i915: make compact dma scatter 
lists creation work with SWIOTLB backend.") as well. So it looks it did 
work behind swiotlb despite those missing calls you highlighted.



Also, correct me if I'm wrong, but the original driver segment size
appears to mean "the largest contiguous area that can be handled either
by the device or the dma mapping layer" rather than the total space
available for dma mappings? Not completely sure what
dma_max_mapping_size() is returning, though?


AFAIU looks to be compatible on paper at least.:

dma_max_mapping_size -> "Returns the maximum size of a mapping for the 
device."


So an individual mapping.

But then in case of swiotlb is implemented in swiotlb_max_mapping_size, 
and not the same code as swiotlb_max_segment. I agree, ideally if 
someone could clarify they are returning the same thing or there is a 
miss somewhere.


Regards,

Tvrtko

Re: [PATCH v5] drm/i915: stop using swiotlb

2022-08-08 Thread Hellstrom, Thomas 
Hi, [back from vacation]

On Tue, 2022-07-26 at 16:39 +0100, Robert Beckett wrote:
> Calling swiotlb functions directly is nowadays considered harmful.
> See
> https://lore.kernel.org/intel-gfx/20220711082614.ga29...@lst.de/
> 
> 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 
> Cc: Tvrtko Ursulin 
> Cc: Thomas Hellstrom 
> Cc: Matthew Auld 
> 
> 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
> v5: - fix checkpatch whitespace issue
> 
> Reviewed-by: Christoph Hellwig 
> Reviewed-by: Tvrtko Ursulin 
> Signed-off-by: Robert Beckett 

Hmm,

This whole thing looks a bit strange to me since with SWIOTLB actually
used for i915, the driver should malfunction anyway as it doesn't do
any dma_sync_sg_for_cpu() or dma_sync_sg_for_device(), and the driver
assumes all coherent dma. Is that SWIOTLB=force kernel option still
available?

Also, correct me if I'm wrong, but the original driver segment size
appears to mean "the largest contiguous area that can be handled either
by the device or the dma mapping layer" rather than the total space
available for dma mappings? Not completely sure what
dma_max_mapping_size() is returning, though?

/Thomas

[PATCH v5] drm/i915: stop using swiotlb

2022-07-26 Thread Robert Beckett 
Calling swiotlb functions directly is nowadays considered harmful. See
https://lore.kernel.org/intel-gfx/20220711082614.ga29...@lst.de/

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 
Cc: Tvrtko Ursulin 
Cc: Thomas Hellstrom 
Cc: Matthew Auld 

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
v5: - fix checkpatch whitespace issue

Reviewed-by: Christoph Hellwig 
Reviewed-by: Tvrtko Ursulin 
Signed-off-by: Robert Beckett 
---
 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  | 16 
 5 files changed, 12 insertions(+), 31 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 
 #include 
-#include 
 
 #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