[PATCH v3 1/3] drm: Add support for GEM buffers backed by non-coherent memory
Paul Cercueil
paul at crapouillou.net
Sat May 15 09:14:17 UTC 2021
Hi Thomas,
Le sam., mai 15 2021 at 11:03:34 +0200, Thomas Zimmermann
<tzimmermann at suse.de> a écrit :
> Hi
>
> Am 14.05.21 um 22:11 schrieb Paul Cercueil:
>> Having GEM buffers backed by non-coherent memory is interesting in
>> the
>> particular case where it is faster to render to a non-coherent buffer
>> then sync the data cache, than to render to a write-combine buffer,
>> and
>> (by extension) much faster than using a shadow buffer. This is true
>> for
>> instance on some Ingenic SoCs, where even simple blits (e.g. memcpy)
>> are about three times faster using this method.
>>
>> Add a 'map_noncoherent' flag to the drm_gem_cma_object structure,
>> which
>> can be set by the drivers when they create the dumb buffer.
>>
>> Since this really only applies to software rendering, disable this
>> flag
>> as soon as the CMA objects are exported via PRIME.
>>
>> v3: New patch. Now uses a simple 'map_noncoherent' flag to control
>> how
>> the objects are mapped, and use the new dma_mmap_pages function.
>>
>> Signed-off-by: Paul Cercueil <paul at crapouillou.net>
>> ---
>> drivers/gpu/drm/drm_gem_cma_helper.c | 41
>> +++++++++++++++++++++++++---
>> include/drm/drm_gem_cma_helper.h | 7 ++++-
>> 2 files changed, 43 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c
>> b/drivers/gpu/drm/drm_gem_cma_helper.c
>> index 7942cf05cd93..81a31bcf7d68 100644
>> --- a/drivers/gpu/drm/drm_gem_cma_helper.c
>> +++ b/drivers/gpu/drm/drm_gem_cma_helper.c
>> @@ -115,8 +115,15 @@ struct drm_gem_cma_object
>> *drm_gem_cma_create(struct drm_device *drm,
>> if (IS_ERR(cma_obj))
>> return cma_obj;
>> - cma_obj->vaddr = dma_alloc_wc(drm->dev, size, &cma_obj->paddr,
>> - GFP_KERNEL | __GFP_NOWARN);
>> + if (cma_obj->map_noncoherent) {
>> + cma_obj->vaddr = dma_alloc_noncoherent(drm->dev, size,
>> + &cma_obj->paddr,
>> + DMA_TO_DEVICE,
>> + GFP_KERNEL | __GFP_NOWARN);
>> + } else {
>> + cma_obj->vaddr = dma_alloc_wc(drm->dev, size, &cma_obj->paddr,
>> + GFP_KERNEL | __GFP_NOWARN);
>> + }
>> if (!cma_obj->vaddr) {
>> drm_dbg(drm, "failed to allocate buffer with size %zu\n",
>> size);
>> @@ -499,8 +506,13 @@ int drm_gem_cma_mmap(struct drm_gem_object
>> *obj, struct vm_area_struct *vma)
>> cma_obj = to_drm_gem_cma_obj(obj);
>> - ret = dma_mmap_wc(cma_obj->base.dev->dev, vma, cma_obj->vaddr,
>> - cma_obj->paddr, vma->vm_end - vma->vm_start);
>> + vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
>> + if (!cma_obj->map_noncoherent)
>> + vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
>> +
>> + ret = dma_mmap_pages(cma_obj->base.dev->dev,
>> + vma, vma->vm_end - vma->vm_start,
>> + virt_to_page(cma_obj->vaddr));
>> if (ret)
>> drm_gem_vm_close(vma);
>> @@ -556,3 +568,24 @@
>> drm_gem_cma_prime_import_sg_table_vmap(struct drm_device *dev,
>> return obj;
>> }
>> EXPORT_SYMBOL(drm_gem_cma_prime_import_sg_table_vmap);
>> +
>> +/**
>> + * drm_gem_cma_prime_mmap - PRIME mmap function for CMA GEM drivers
>> + * @obj: GEM object
>> + * @vma: Virtual address range
>> + *
>> + * Carbon copy of drm_gem_prime_mmap, but the 'map_noncoherent'
>> flag is
>> + * disabled to ensure that the exported buffers have the expected
>> cache
>> + * coherency.
>> + */
>> +int drm_gem_cma_prime_mmap(struct drm_gem_object *obj,
>> + struct vm_area_struct *vma)
>> +{
>> + struct drm_gem_cma_object *cma_obj = to_drm_gem_cma_obj(obj);
>> +
>> + /* Use standard cache settings for PRIME-exported GEM buffers */
>> + cma_obj->map_noncoherent = false;
>> +
>> + return drm_gem_prime_mmap(obj, vma);
>> +}
>> +EXPORT_SYMBOL(drm_gem_cma_prime_mmap);
>> diff --git a/include/drm/drm_gem_cma_helper.h
>> b/include/drm/drm_gem_cma_helper.h
>> index 0a9711caa3e8..b597e00fd5f6 100644
>> --- a/include/drm/drm_gem_cma_helper.h
>> +++ b/include/drm/drm_gem_cma_helper.h
>> @@ -16,6 +16,7 @@ struct drm_mode_create_dumb;
>> * more than one entry but they are guaranteed to have
>> contiguous
>> * DMA addresses.
>> * @vaddr: kernel virtual address of the backing memory
>> + * @map_noncoherent: if true, the GEM object is backed by
>> non-coherent memory
>> */
>> struct drm_gem_cma_object {
>> struct drm_gem_object base;
>> @@ -24,6 +25,8 @@ struct drm_gem_cma_object {
>> /* For objects with DMA memory allocated by GEM CMA */
>> void *vaddr;
>> +
>> + bool map_noncoherent;
>> };
>> #define to_drm_gem_cma_obj(gem_obj) \
>> @@ -119,7 +122,7 @@ int drm_gem_cma_mmap(struct drm_gem_object *obj,
>> struct vm_area_struct *vma);
>> .prime_handle_to_fd = drm_gem_prime_handle_to_fd, \
>> .prime_fd_to_handle = drm_gem_prime_fd_to_handle, \
>> .gem_prime_import_sg_table = drm_gem_cma_prime_import_sg_table, \
>> - .gem_prime_mmap = drm_gem_prime_mmap
>> + .gem_prime_mmap = drm_gem_cma_prime_mmap
>
> gem_prime_mmap is deprecated and on the way out. Only mmap in
> drm_gem_object_funcs should be used. I have patches for other drivers
> that convert everything to drm_gem_prime_mmap. Afterwards the pointer
> can be removed.
>
> Rather than writing a custom prime mmap function, update
> drm_gem_cma_prime_import_sg_table() so that it disables non-coherent
> mappings for imported buffers. For an example, see how SHMEM's
> internal create function uses the 'private' parameter. [1]
Alright, I can do that.
Cheers,
-Paul
> Best regards
> Thomas
>
> [1]
> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_gem_shmem_helper.c#L39
>
>> /**
>> * DRM_GEM_CMA_DRIVER_OPS - CMA GEM driver operations
>> @@ -181,5 +184,7 @@ struct drm_gem_object *
>> drm_gem_cma_prime_import_sg_table_vmap(struct drm_device *drm,
>> struct dma_buf_attachment *attach,
>> struct sg_table *sgt);
>> +int drm_gem_cma_prime_mmap(struct drm_gem_object *obj,
>> + struct vm_area_struct *vma);
>> #endif /* __DRM_GEM_CMA_HELPER_H__ */
>>
>
> --
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
> Geschäftsführer: Felix Imendörffer
>
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