On Wed, Dec 11, 2019 at 01:19:53PM +0100, Gerd Hoffmann wrote:
> The callback allows drivers and helpers to tweak pgprot for mappings.
> This is especially helpful when using shmem helpers. It allows drivers
> to switch mappings from writecombine (default) to something else (cached
> for example) on a per-object base without having to supply their own
> mmap() and vmap() functions.
>
> The patch also adds two implementations for the callback, for cached and
> writecombine mappings, and the drm_gem_pgprot() function to update
> pgprot for a given object, using the new &drm_gem_object_funcs.pgprot
> callback if available.
>
> Signed-off-by: Gerd Hoffmann <kraxel@xxxxxxxxxx>
> ---
> include/drm/drm_gem.h | 15 +++++++++++++
> drivers/gpu/drm/drm_gem.c | 46 ++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 60 insertions(+), 1 deletion(-)
>
> diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
> index 0b375069cd48..5beef7226e69 100644
> --- a/include/drm/drm_gem.h
> +++ b/include/drm/drm_gem.h
> @@ -163,6 +163,17 @@ struct drm_gem_object_funcs {
> */
> int (*mmap)(struct drm_gem_object *obj, struct vm_area_struct *vma);
>
> + /**
> + * @pgprot:
> + *
> + * Tweak pgprot as needed, typically used to set cache bits.
> + *
> + * This callback is optional.
> + *
> + * If unset drm_gem_pgprot_wc() will be used.
> + */
> + pgprot_t (*pgprot)(struct drm_gem_object *obj, pgprot_t prot);
I kinda prefer v1, mostly because this is a huge can of worms, and solving
this properly is going to be real hard (and will necessarily involve
dma-buf and dma-api and probably more). Charging ahead here just risks
that we dig ourselves into a corner. You're v1 is maybe not the most
clean, but just a few code bits here&there should be more flexible and
easier to hack on and experiment around with.
-Daniel
> +
> /**
> * @vm_ops:
> *
> @@ -350,6 +361,10 @@ int drm_gem_mmap_obj(struct drm_gem_object *obj, unsigned long obj_size,
> struct vm_area_struct *vma);
> int drm_gem_mmap(struct file *filp, struct vm_area_struct *vma);
>
> +pgprot_t drm_gem_pgprot_cached(struct drm_gem_object *obj, pgprot_t prot);
> +pgprot_t drm_gem_pgprot_wc(struct drm_gem_object *obj, pgprot_t prot);
> +pgprot_t drm_gem_pgprot(struct drm_gem_object *obj, pgprot_t prot);
> +
> /**
> * drm_gem_object_get - acquire a GEM buffer object reference
> * @obj: GEM buffer object
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index 56f42e0f2584..1c468fe8e342 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -1119,7 +1119,8 @@ int drm_gem_mmap_obj(struct drm_gem_object *obj, unsigned long obj_size,
> return -EINVAL;
>
> vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
> - vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
> + vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
> + vma->vm_page_prot = drm_gem_pgprot(obj, vma->vm_page_prot);
> vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
> }
>
> @@ -1210,6 +1211,49 @@ int drm_gem_mmap(struct file *filp, struct vm_area_struct *vma)
> }
> EXPORT_SYMBOL(drm_gem_mmap);
>
> +/**
> + * drm_gem_mmap - update pgprot for objects needing a cachable mapping.
> + * @obj: the GEM object.
> + * @prot: page attributes.
> + *
> + * This function can be used as &drm_gem_object_funcs.pgprot callback.
> + */
> +pgprot_t drm_gem_pgprot_cached(struct drm_gem_object *obj, pgprot_t prot)
> +{
> + return prot;
> +}
> +EXPORT_SYMBOL(drm_gem_pgprot_cached);
> +
> +/**
> + * drm_gem_mmap - update pgprot for objects needing a wc mapping.
> + * @obj: the GEM object.
> + * @prot: page attributes.
> + *
> + * This function can be used as &drm_gem_object_funcs.pgprot callback.
> + */
> +pgprot_t drm_gem_pgprot_wc(struct drm_gem_object *obj, pgprot_t prot)
> +{
> + return pgprot_writecombine(prot);
> +}
> +EXPORT_SYMBOL(drm_gem_pgprot_wc);
> +
> +/**
> + * drm_gem_mmap - update pgprot for a given gem object.
> + * @obj: the GEM object.
> + * @prot: page attributes.
> + *
> + * This function updates pgprot according to the needs of the given
> + * object. If present &drm_gem_object_funcs.pgprot callback will be
> + * used, otherwise drm_gem_pgprot_wc() is called.
> + */
> +pgprot_t drm_gem_pgprot(struct drm_gem_object *obj, pgprot_t prot)
> +{
> + if (obj->funcs->pgprot)
> + return obj->funcs->pgprot(obj, prot);
> + return drm_gem_pgprot_wc(obj, prot);
> +}
> +EXPORT_SYMBOL(drm_gem_pgprot);
> +
> void drm_gem_print_info(struct drm_printer *p, unsigned int indent,
> const struct drm_gem_object *obj)
> {
> --
> 2.18.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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