[PATCH 3/5] drm: Add infrastructure for vmap operations of I/O memory
daniel at ffwll.ch
daniel at ffwll.ch
Wed Jul 29 13:57:44 UTC 2020
On Wed, Jul 29, 2020 at 03:41:46PM +0200, Thomas Zimmermann wrote:
> Most platforms allow for accessing framebuffer I/O memory with regular
> load and store operations. Some platforms, such as sparc64, require
> the use of special instructions instead.
>
> This patch adds vmap_iomem to struct drm_gem_object_funcs. The new
> interface drm_client_buffer_vmap_iomem() gives DRM clients access to the
> I/O memory buffer. The semantics of struct drm_gem_objcet_funcs.vmap
> change slightly. It used to return system or I/O memory. Now it is
> expected to return memory addresses that can be accessed with regular
> load and store operations. So nothing changes for existing implementations
> of GEM objects. If the GEM object also implements vmap_iomem, a call
> to vmap shall only return system memory, even if I/O memory could be
> accessed with loads and stores.
>
> The existing interface drm_client_buffer_vmap() shall only return memory
> as given by drm_gem_vmap ((i.e., that is accessible via regular load and
> store). The new interface drm_client_buffer_vmap_iomem() shall only
> return I/O memory.
>
> DRM clients must map buffers by calling drm_client_buffer_vmap_iomem()
> and drm_client_buffer_vmap() to get the buffer in I/O or system memory.
> Each function returns NULL if the buffer is in the other memory area.
> Depending on the type of the returned memory, clients must access the
> framebuffer with the appropriate operations.
>
> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
Hm I don't think this works, since for more dynamic framebuffers (like
real big gpu ttm drivers) this is a dynamic thing, which can change every
time we do an mmap. So I think the ttm approach of having an is_iomem flag
is a lot better.
The trouble with that is that you don't have correct checking of sparse
mappings, but oh well :-/ The one idea I've had to address that is using
something like this
typedef dma_buf_addr_t {
bool is_iomem;
union {
void __iomem *vaddr_iomem;
void vaddr;
};
};
And then having a wrapper for memcpy_from_dma_buf_addr and
memcpy_to_dma_buf_addr, which switches between memcpy and memcpy_from/toio
depending upon the is_iomem flag.
But it's a lot more invasive unfortunately :-/
-Daniel
> ---
> drivers/gpu/drm/drm_client.c | 52 ++++++++++++++++++++++++++++++++--
> drivers/gpu/drm/drm_gem.c | 19 +++++++++++++
> drivers/gpu/drm/drm_internal.h | 1 +
> include/drm/drm_client.h | 8 +++++-
> include/drm/drm_gem.h | 17 +++++++++--
> 5 files changed, 91 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_client.c b/drivers/gpu/drm/drm_client.c
> index 495f47d23d87..b5bbe089a41e 100644
> --- a/drivers/gpu/drm/drm_client.c
> +++ b/drivers/gpu/drm/drm_client.c
> @@ -327,6 +327,46 @@ void *drm_client_buffer_vmap(struct drm_client_buffer *buffer)
> }
> EXPORT_SYMBOL(drm_client_buffer_vmap);
>
> +/**
> + * drm_client_buffer_vmap_iomem - Map DRM client buffer into address space
> + * @buffer: DRM client buffer
> + *
> + * This function maps a client buffer into kernel address space. If the
> + * buffer is already mapped, it returns the mapping's address.
> + *
> + * Client buffer mappings are not ref'counted. Each call to
> + * drm_client_buffer_vmap() should be followed by a call to
> + * drm_client_buffer_vunmap(); or the client buffer should be mapped
> + * throughout its lifetime.
> + *
> + * Returns:
> + * The mapped memory's address
> + */
> +void __iomem *drm_client_buffer_vmap_iomem(struct drm_client_buffer *buffer)
> +{
> + void __iomem *vaddr_iomem;
> +
> + if (buffer->vaddr_iomem)
> + return buffer->vaddr_iomem;
> +
> + /*
> + * FIXME: The dependency on GEM here isn't required, we could
> + * convert the driver handle to a dma-buf instead and use the
> + * backend-agnostic dma-buf vmap support instead. This would
> + * require that the handle2fd prime ioctl is reworked to pull the
> + * fd_install step out of the driver backend hooks, to make that
> + * final step optional for internal users.
> + */
> + vaddr_iomem = drm_gem_vmap_iomem(buffer->gem);
> + if (IS_ERR(vaddr_iomem))
> + return vaddr_iomem;
> +
> + buffer->vaddr_iomem = vaddr_iomem;
> +
> + return vaddr_iomem;
> +}
> +EXPORT_SYMBOL(drm_client_buffer_vmap_iomem);
> +
> /**
> * drm_client_buffer_vunmap - Unmap DRM client buffer
> * @buffer: DRM client buffer
> @@ -337,8 +377,16 @@ EXPORT_SYMBOL(drm_client_buffer_vmap);
> */
> void drm_client_buffer_vunmap(struct drm_client_buffer *buffer)
> {
> - drm_gem_vunmap(buffer->gem, buffer->vaddr);
> - buffer->vaddr = NULL;
> + drm_WARN_ON(buffer->client->dev, buffer->vaddr && buffer->vaddr_iomem);
> +
> + if (buffer->vaddr) {
> + drm_gem_vunmap(buffer->gem, buffer->vaddr);
> + buffer->vaddr = NULL;
> + }
> + if (buffer->vaddr_iomem) {
> + drm_gem_vunmap(buffer->gem, (void *)buffer->vaddr_iomem);
> + buffer->vaddr_iomem = NULL;
> + }
> }
> EXPORT_SYMBOL(drm_client_buffer_vunmap);
>
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index a57f5379fc08..a001be8c0965 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -1227,6 +1227,25 @@ void *drm_gem_vmap(struct drm_gem_object *obj)
> vaddr = obj->funcs->vmap(obj);
> else if (obj->dev->driver->gem_prime_vmap)
> vaddr = obj->dev->driver->gem_prime_vmap(obj);
> + else if (obj->funcs && obj->funcs->vmap_iomem)
> + vaddr = NULL; /* requires mapping as I/O memory */
> + else
> + vaddr = ERR_PTR(-EOPNOTSUPP);
> +
> + if (!vaddr)
> + vaddr = ERR_PTR(-ENOMEM);
> +
> + return vaddr;
> +}
> +
> +void __iomem *drm_gem_vmap_iomem(struct drm_gem_object *obj)
> +{
> + void __iomem *vaddr;
> +
> + if (obj->funcs && obj->funcs->vmap_iomem)
> + vaddr = obj->funcs->vmap_iomem(obj);
> + else if (obj->funcs && obj->funcs->vmap)
> + vaddr = NULL; /* requires mapping as system memory */
> else
> vaddr = ERR_PTR(-EOPNOTSUPP);
>
> diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h
> index 8e01caaf95cc..aa1a3d4f9223 100644
> --- a/drivers/gpu/drm/drm_internal.h
> +++ b/drivers/gpu/drm/drm_internal.h
> @@ -187,6 +187,7 @@ void drm_gem_print_info(struct drm_printer *p, unsigned int indent,
> int drm_gem_pin(struct drm_gem_object *obj);
> void drm_gem_unpin(struct drm_gem_object *obj);
> void *drm_gem_vmap(struct drm_gem_object *obj);
> +void __iomem *drm_gem_vmap_iomem(struct drm_gem_object *obj);
> void drm_gem_vunmap(struct drm_gem_object *obj, void *vaddr);
>
> /* drm_debugfs.c drm_debugfs_crc.c */
> diff --git a/include/drm/drm_client.h b/include/drm/drm_client.h
> index 7aaea665bfc2..94aa075ee4b6 100644
> --- a/include/drm/drm_client.h
> +++ b/include/drm/drm_client.h
> @@ -141,10 +141,15 @@ struct drm_client_buffer {
> struct drm_gem_object *gem;
>
> /**
> - * @vaddr: Virtual address for the buffer
> + * @vaddr: Virtual address for the buffer in system memory
> */
> void *vaddr;
>
> + /**
> + * @vaddr: Virtual address for the buffer in I/O memory
> + */
> + void *vaddr_iomem;
> +
> /**
> * @fb: DRM framebuffer
> */
> @@ -156,6 +161,7 @@ drm_client_framebuffer_create(struct drm_client_dev *client, u32 width, u32 heig
> void drm_client_framebuffer_delete(struct drm_client_buffer *buffer);
> int drm_client_framebuffer_flush(struct drm_client_buffer *buffer, struct drm_rect *rect);
> void *drm_client_buffer_vmap(struct drm_client_buffer *buffer);
> +void __iomem *drm_client_buffer_vmap_iomem(struct drm_client_buffer *buffer);
> void drm_client_buffer_vunmap(struct drm_client_buffer *buffer);
>
> int drm_client_modeset_create(struct drm_client_dev *client);
> diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
> index 337a48321705..bc735ff522a8 100644
> --- a/include/drm/drm_gem.h
> +++ b/include/drm/drm_gem.h
> @@ -134,17 +134,28 @@ struct drm_gem_object_funcs {
> * @vmap:
> *
> * Returns a virtual address for the buffer. Used by the
> - * drm_gem_dmabuf_vmap() helper.
> + * drm_gem_dmabuf_vmap() helper. If the buffer is not
> + * located in system memory, the function returns NULL.
> *
> * This callback is optional.
> */
> void *(*vmap)(struct drm_gem_object *obj);
>
> + /**
> + * @vmap_iomem:
> + *
> + * Returns a virtual address for the buffer. If the buffer is not
> + * located in I/O memory, the function returns NULL.
> + *
> + * This callback is optional.
> + */
> + void __iomem *(*vmap_iomem)(struct drm_gem_object *obj);
> +
> /**
> * @vunmap:
> *
> - * Releases the address previously returned by @vmap. Used by the
> - * drm_gem_dmabuf_vunmap() helper.
> + * Releases the address previously returned by @vmap or @vmap_iomem.
> + * Used by the drm_gem_dmabuf_vunmap() helper.
> *
> * This callback is optional.
> */
> --
> 2.27.0
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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