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Date: Tue, 26 Jul 2022 15:24:27 +0100
From: Robert Beckett <bob.beckett@...labora.com>
To: Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
Jani Nikula <jani.nikula@...ux.intel.com>,
Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
Rodrigo Vivi <rodrigo.vivi@...el.com>,
David Airlie <airlied@...ux.ie>,
Daniel Vetter <daniel@...ll.ch>
Cc: kernel@...labora.com, Christoph Hellwig <hch@....de>,
Thomas Hellstrom <thomas.hellstrom@...el.com>,
Matthew Auld <matthew.auld@...el.com>,
Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] drm/i915: stop using swiotlb
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@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 <hch@....de>
>> Cc: Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
>> Cc: Thomas Hellstrom <thomas.hellstrom@...el.com>
>> Cc: Matthew Auld <matthew.auld@...el.com>
>>
>> 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@....de>
>> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@...el.com>
>> Signed-off-by: Robert Beckett <bob.beckett@...labora.com>
>> ---
>> 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);
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