[PATCH 1/3] drm/shmem-helper: Import dmabuf without mapping its sg_table
oushixiong
oushixiong1025 at 163.com
Mon May 5 15:11:09 UTC 2025
Hi Christian,
I don't see strong relevance between my patch and the patches you're
referring to.
Because the drm_gem_prime_import() function imports sg_table by default,
my patch provides an alternative
import callback implementation for SHMEM-based drivers that differs from
drm_gem_prime_import().
drm_gem_shmem_prime_import_sg_table() doesn't need to call
dma_buf_map_attachment_unlocked() to import sg_table.
Alternatively, I might not have fully understood the patches you mentioned.
Thanks and Regards,
Shixiong.
在 2025/5/5 22:32, Christian König 写道:
> Hi Shixiong,
>
> for drm changes please base your patches on drm-misc-next or drm-next.
>
> That is probably fixed by this one here:
>
> commit b72f66f22c0e39ae6684c43fead774c13db24e73
> Author: Christian König <christian.koenig at amd.com>
> Date: Tue Feb 11 17:20:53 2025 +0100
>
> dma-buf: drop caching of sg_tables
>
> That was purely for the transition from static to dynamic dma-buf
> handling and can be removed again now.
>
> Signed-off-by: Christian König <christian.koenig at amd.com>
> Reviewed-by: Simona Vetter <simona.vetter at ffwll.ch>
> Reviewed-by: Dmitry Osipenko <dmitry.osipenko at collabora.com>
> Link: https://patchwork.freedesktop.org/patch/msgid/20250211163109.12200-5-christian.koenig@amd.com
>
> After this patch SG tables where only created when necessary.
>
> Regards,
> Christian.
>
> On 5/5/25 16:22, oushixiong wrote:
>> Hi Christian,
>>
>> My patch is based on linux-next, so this patch is not based on the latest code. Then, I'd like to ask which patch resolved the issue with sg-tables?
>>
>>
>> Thanks and Regards,
>>
>> Shixiong.
>>
>>
>> 在 2025/5/5 19:25, Christian König 写道:
>>> Hi Thomas & Shixiong,
>>>
>>> first of all the patch is still based on outdated code. For example the cache_sgt_mapping member is already removed in drm-misc-next.
>>>
>>> So if I'm not completely mistaken the issue is already resolved upstream.
>>>
>>> Regards,
>>> Christian.
>>>
>>> On 5/5/25 13:12, Thomas Zimmermann wrote:
>>>> (cc'ing Christian)
>>>>
>>>> Hi,
>>>>
>>>> I don't feel qualified to fully review this patch.
>>>>
>>>> It would be good to have the issue with sg-tables solved, but I dislike the dedicated initializer macros. So my question is if this has any drawbacks. Or could we make this available and the default for all shmem-based drivers?
>>>>
>>>> Best regards
>>>> Thomas
>>>>
>>>> Am 01.05.25 um 08:43 schrieb oushixiong1025 at 163.com:
>>>>> From: Shixiong Ou <oushixiong at kylinos.cn>
>>>>>
>>>>> [WHY]
>>>>> 1. Drivers using DRM_GEM_SHADOW_PLANE_HELPER_FUNCS and
>>>>> DRM_GEM_SHMEM_DRIVER_OPS (e.g., udl, ast) do not require
>>>>> sg_table import.
>>>>> They only need dma_buf_vmap() to access the shared buffer's
>>>>> kernel virtual address.
>>>>>
>>>>> 2. On certain Aspeed-based boards, a dma_mask of 0xffff_ffff may
>>>>> trigger SWIOTLB during dmabuf import. However, IO_TLB_SEGSIZE
>>>>> restricts the maximum DMA streaming mapping memory, resulting in
>>>>> errors like:
>>>>>
>>>>> ast 0000:07:00.0: swiotlb buffer is full (sz: 3145728 bytes), total 32768 (slots), used 0 (slots)
>>>>>
>>>>> [HOW]
>>>>> Provide a gem_prime_import implementation without sg_table mapping
>>>>> to avoid issues (e.g., "swiotlb buffer is full"). Drivers that do not
>>>>> require sg_table can adopt this.
>>>>>
>>>>> Signed-off-by: Shixiong Ou <oushixiong at kylinos.cn>
>>>>> ---
>>>>> drivers/gpu/drm/drm_gem_shmem_helper.c | 95 ++++++++++++++++++++++++++
>>>>> include/drm/drm_gem_shmem_helper.h | 24 +++++++
>>>>> 2 files changed, 119 insertions(+)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
>>>>> index d99dee67353a..9e41e350ff6f 100644
>>>>> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
>>>>> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
>>>>> @@ -39,6 +39,7 @@ MODULE_IMPORT_NS("DMA_BUF");
>>>>> static const struct drm_gem_object_funcs drm_gem_shmem_funcs = {
>>>>> .free = drm_gem_shmem_object_free,
>>>>> .print_info = drm_gem_shmem_object_print_info,
>>>>> + .export = drm_gem_shmem_object_prime_export,
>>>>> .pin = drm_gem_shmem_object_pin,
>>>>> .unpin = drm_gem_shmem_object_unpin,
>>>>> .get_sg_table = drm_gem_shmem_object_get_sg_table,
>>>>> @@ -799,6 +800,100 @@ drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
>>>>> }
>>>>> EXPORT_SYMBOL_GPL(drm_gem_shmem_prime_import_sg_table);
>>>>> +const struct dma_buf_ops drm_gem_shmem_prime_dmabuf_ops = {
>>>>> + .cache_sgt_mapping = true,
>>>>> + .attach = drm_gem_map_attach,
>>>>> + .detach = drm_gem_map_detach,
>>>>> + .map_dma_buf = drm_gem_map_dma_buf,
>>>>> + .unmap_dma_buf = drm_gem_unmap_dma_buf,
>>>>> + .release = drm_gem_dmabuf_release,
>>>>> + .mmap = drm_gem_dmabuf_mmap,
>>>>> + .vmap = drm_gem_dmabuf_vmap,
>>>>> + .vunmap = drm_gem_dmabuf_vunmap,
>>>>> +};
>>>>> +
>>>>> +/**
>>>>> + * drm_gem_shmem_prime_export - implementation of the export callback
>>>>> + * @shmem: shmem GEM object
>>>>> + */
>>>>> +struct dma_buf *drm_gem_shmem_prime_export(struct drm_gem_shmem_object *shmem,
>>>>> + int flags)
>>>>> +{
>>>>> + struct drm_gem_object *obj = &shmem->base;
>>>>> + struct drm_device *dev = obj->dev;
>>>>> + struct dma_buf_export_info exp_info = {
>>>>> + .exp_name = KBUILD_MODNAME, /* white lie for debug */
>>>>> + .owner = dev->driver->fops->owner,
>>>>> + .ops = &drm_gem_shmem_prime_dmabuf_ops,
>>>>> + .size = obj->size,
>>>>> + .flags = flags,
>>>>> + .priv = obj,
>>>>> + .resv = obj->resv,
>>>>> + };
>>>>> +
>>>>> + return drm_gem_dmabuf_export(dev, &exp_info);
>>>>> +}
>>>>> +
>>>>> +/**
>>>>> + * drm_gem_shmem_prime_import - Import dmabuf without mapping its sg_table
>>>>> + * @dev: Device to import into
>>>>> + * @dma_buf: dma-buf object to import
>>>>> + *
>>>>> + * Drivers that use the shmem helpers but also wants to import dmabuf without
>>>>> + * mapping its sg_table can use this as their &drm_driver.gem_prime_import
>>>>> + * implementation.
>>>>> + */
>>>>> +struct drm_gem_object *drm_gem_shmem_prime_import(struct drm_device *dev,
>>>>> + struct dma_buf *dma_buf)
>>>>> +{
>>>>> + struct dma_buf_attachment *attach;
>>>>> + struct drm_gem_shmem_object *shmem;
>>>>> + size_t size;
>>>>> + int ret;
>>>>> +
>>>>> + if (dma_buf->ops == &drm_gem_shmem_prime_dmabuf_ops) {
>>>>> + struct drm_gem_object *obj;
>>>>> +
>>>>> + obj = dma_buf->priv;
>>>>> + if (obj->dev == dev) {
>>>>> + /*
>>>>> + * Importing dmabuf exported from our own gem increases
>>>>> + * refcount on gem itself instead of f_count of dmabuf.
>>>>> + */
>>>>> + drm_gem_object_get(obj);
>>>>> + return obj;
>>>>> + }
>>>>> + }
>>>>> +
>>>>> + attach = dma_buf_attach(dma_buf, dev->dev);
>>>>> + if (IS_ERR(attach))
>>>>> + return ERR_CAST(attach);
>>>>> +
>>>>> + get_dma_buf(dma_buf);
>>>>> +
>>>>> + size = PAGE_ALIGN(attach->dmabuf->size);
>>>>> +
>>>>> + shmem = __drm_gem_shmem_create(dev, size, true, NULL);
>>>>> + if (IS_ERR(shmem)) {
>>>>> + ret = PTR_ERR(shmem);
>>>>> + goto fail_detach;
>>>>> + }
>>>>> +
>>>>> + drm_dbg_prime(dev, "size = %zu\n", size);
>>>>> +
>>>>> + shmem->base.import_attach = attach;
>>>>> + shmem->base.resv = dma_buf->resv;
>>>>> +
>>>>> + return &shmem->base;
>>>>> +
>>>>> +fail_detach:
>>>>> + dma_buf_detach(dma_buf, attach);
>>>>> + dma_buf_put(dma_buf);
>>>>> +
>>>>> + return ERR_PTR(ret);
>>>>> +}
>>>>> +EXPORT_SYMBOL_GPL(drm_gem_shmem_prime_import);
>>>>> +
>>>>> MODULE_DESCRIPTION("DRM SHMEM memory-management helpers");
>>>>> MODULE_IMPORT_NS("DMA_BUF");
>>>>> MODULE_LICENSE("GPL v2");
>>>>> diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
>>>>> index cef5a6b5a4d6..78ef91593a8e 100644
>>>>> --- a/include/drm/drm_gem_shmem_helper.h
>>>>> +++ b/include/drm/drm_gem_shmem_helper.h
>>>>> @@ -110,6 +110,8 @@ int drm_gem_shmem_vmap(struct drm_gem_shmem_object *shmem,
>>>>> void drm_gem_shmem_vunmap(struct drm_gem_shmem_object *shmem,
>>>>> struct iosys_map *map);
>>>>> int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct *vma);
>>>>> +struct dma_buf *drm_gem_shmem_prime_export(struct drm_gem_shmem_object *shmem,
>>>>> + int flags);
>>>>> int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem);
>>>>> void drm_gem_shmem_unpin_locked(struct drm_gem_shmem_object *shmem);
>>>>> @@ -168,6 +170,18 @@ static inline void drm_gem_shmem_object_print_info(struct drm_printer *p, unsign
>>>>> drm_gem_shmem_print_info(shmem, p, indent);
>>>>> }
>>>>> +/**
>>>>> + * drm_gem_shmem_object_prime_export - GEM object function for export()
>>>>> + * @obj: GEM object
>>>>> + *
>>>>> + */
>>>>> +static inline struct dma_buf *drm_gem_shmem_object_prime_export(struct drm_gem_object *obj,
>>>>> + int flags)
>>>>> +{
>>>>> + struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
>>>>> +
>>>>> + return drm_gem_shmem_prime_export(shmem, flags);
>>>>> +}
>>>>> /**
>>>>> * drm_gem_shmem_object_pin - GEM object function for drm_gem_shmem_pin()
>>>>> * @obj: GEM object
>>>>> @@ -276,6 +290,8 @@ drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
>>>>> struct sg_table *sgt);
>>>>> int drm_gem_shmem_dumb_create(struct drm_file *file, struct drm_device *dev,
>>>>> struct drm_mode_create_dumb *args);
>>>>> +struct drm_gem_object *drm_gem_shmem_prime_import(struct drm_device *dev,
>>>>> + struct dma_buf *buf);
>>>>> /**
>>>>> * DRM_GEM_SHMEM_DRIVER_OPS - Default shmem GEM operations
>>>>> @@ -287,4 +303,12 @@ int drm_gem_shmem_dumb_create(struct drm_file *file, struct drm_device *dev,
>>>>> .gem_prime_import_sg_table = drm_gem_shmem_prime_import_sg_table, \
>>>>> .dumb_create = drm_gem_shmem_dumb_create
>>>>> +/**
>>>>> + * This macro provides a shmem GEM operations that implementate a simple
>>>>> + * gem_prime_import.
>>>>> + */
>>>>> +#define DRM_GEM_SHMEM_SIMPLE_DRIVER_OPS \
>>>>> + .gem_prime_import = drm_gem_shmem_prime_import, \
>>>>> + .dumb_create = drm_gem_shmem_dumb_create
>>>>> +
>>>>> #endif /* __DRM_GEM_SHMEM_HELPER_H__ */
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