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SubjectRe: [PATCH 2/4] dma-buf: add support for kernel cpu access
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On Sun, Mar 18, 2012 at 6:34 PM, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> Big differences to other contenders in the field (like ion) is
> that this also supports highmem, so we have to split up the cpu
> access from the kernel side into a prepare and a kmap step.
>
> Prepare is allowed to fail and should do everything required so that
> the kmap calls can succeed (like swapin/backing storage allocation,
> flushing, ...).
>
> More in-depth explanations will follow in the follow-up documentation
> patch.
>
> Changes in v2:
>
> - Clear up begin_cpu_access confusion noticed by Sumit Semwal.
> - Don't automatically fallback from the _atomic variants to the
>  non-atomic variants. The _atomic callbacks are not allowed to
>  sleep, so we want exporters to make this decision explicit. The
>  function signatures are explicit, so simpler exporters can still
>  use the same function for both.
> - Make the unmap functions optional. Simpler exporters with permanent
>  mappings don't need to do anything at unmap time.
>
> Changes in v3:
>
> - Adjust the WARN_ON checks for the new ->ops functions as suggested
>  by Rob Clark and Sumit Semwal.
> - Rebased on top of latest dma-buf-next git.
>
> Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Signed-off-by: Rob Clark <rob@ti.com>

note: we should start updating the individual driver support for drm
drivers for this (since Dave has prime working now), although this
should not block the drm-core support for prime/dmabuf

BR,
-R

> ---
>  drivers/base/dma-buf.c  |  124 ++++++++++++++++++++++++++++++++++++++++++++++-
>  include/linux/dma-buf.h |   59 ++++++++++++++++++++++
>  2 files changed, 182 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/base/dma-buf.c b/drivers/base/dma-buf.c
> index 5641b9c..2226511 100644
> --- a/drivers/base/dma-buf.c
> +++ b/drivers/base/dma-buf.c
> @@ -80,7 +80,9 @@ struct dma_buf *dma_buf_export(void *priv, const struct dma_buf_ops *ops,
>        if (WARN_ON(!priv || !ops
>                          || !ops->map_dma_buf
>                          || !ops->unmap_dma_buf
> -                         || !ops->release)) {
> +                         || !ops->release
> +                         || !ops->kmap_atomic
> +                         || !ops->kmap)) {
>                return ERR_PTR(-EINVAL);
>        }
>
> @@ -284,3 +286,123 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
>                                                direction);
>  }
>  EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
> +
> +
> +/**
> + * dma_buf_begin_cpu_access - Must be called before accessing a dma_buf from the
> + * cpu in the kernel context. Calls begin_cpu_access to allow exporter-specific
> + * preparations. Coherency is only guaranteed in the specified range for the
> + * specified access direction.
> + * @dma_buf:   [in]    buffer to prepare cpu access for.
> + * @start:     [in]    start of range for cpu access.
> + * @len:       [in]    length of range for cpu access.
> + * @direction: [in]    length of range for cpu access.
> + *
> + * Can return negative error values, returns 0 on success.
> + */
> +int dma_buf_begin_cpu_access(struct dma_buf *dmabuf, size_t start, size_t len,
> +                            enum dma_data_direction direction)
> +{
> +       int ret = 0;
> +
> +       if (WARN_ON(!dmabuf))
> +               return EINVAL;
> +
> +       if (dmabuf->ops->begin_cpu_access)
> +               ret = dmabuf->ops->begin_cpu_access(dmabuf, start, len, direction);
> +
> +       return ret;
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_begin_cpu_access);
> +
> +/**
> + * dma_buf_end_cpu_access - Must be called after accessing a dma_buf from the
> + * cpu in the kernel context. Calls end_cpu_access to allow exporter-specific
> + * actions. Coherency is only guaranteed in the specified range for the
> + * specified access direction.
> + * @dma_buf:   [in]    buffer to complete cpu access for.
> + * @start:     [in]    start of range for cpu access.
> + * @len:       [in]    length of range for cpu access.
> + * @direction: [in]    length of range for cpu access.
> + *
> + * This call must always succeed.
> + */
> +void dma_buf_end_cpu_access(struct dma_buf *dmabuf, size_t start, size_t len,
> +                           enum dma_data_direction direction)
> +{
> +       WARN_ON(!dmabuf);
> +
> +       if (dmabuf->ops->end_cpu_access)
> +               dmabuf->ops->end_cpu_access(dmabuf, start, len, direction);
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_end_cpu_access);
> +
> +/**
> + * dma_buf_kmap_atomic - Map a page of the buffer object into kernel address
> + * space. The same restrictions as for kmap_atomic and friends apply.
> + * @dma_buf:   [in]    buffer to map page from.
> + * @page_num:  [in]    page in PAGE_SIZE units to map.
> + *
> + * This call must always succeed, any necessary preparations that might fail
> + * need to be done in begin_cpu_access.
> + */
> +void *dma_buf_kmap_atomic(struct dma_buf *dmabuf, unsigned long page_num)
> +{
> +       WARN_ON(!dmabuf);
> +
> +       return dmabuf->ops->kmap_atomic(dmabuf, page_num);
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_kmap_atomic);
> +
> +/**
> + * dma_buf_kunmap_atomic - Unmap a page obtained by dma_buf_kmap_atomic.
> + * @dma_buf:   [in]    buffer to unmap page from.
> + * @page_num:  [in]    page in PAGE_SIZE units to unmap.
> + * @vaddr:     [in]    kernel space pointer obtained from dma_buf_kmap_atomic.
> + *
> + * This call must always succeed.
> + */
> +void dma_buf_kunmap_atomic(struct dma_buf *dmabuf, unsigned long page_num,
> +                          void *vaddr)
> +{
> +       WARN_ON(!dmabuf);
> +
> +       if (dmabuf->ops->kunmap_atomic)
> +               dmabuf->ops->kunmap_atomic(dmabuf, page_num, vaddr);
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_kunmap_atomic);
> +
> +/**
> + * dma_buf_kmap - Map a page of the buffer object into kernel address space. The
> + * same restrictions as for kmap and friends apply.
> + * @dma_buf:   [in]    buffer to map page from.
> + * @page_num:  [in]    page in PAGE_SIZE units to map.
> + *
> + * This call must always succeed, any necessary preparations that might fail
> + * need to be done in begin_cpu_access.
> + */
> +void *dma_buf_kmap(struct dma_buf *dmabuf, unsigned long page_num)
> +{
> +       WARN_ON(!dmabuf);
> +
> +       return dmabuf->ops->kmap(dmabuf, page_num);
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_kmap);
> +
> +/**
> + * dma_buf_kunmap - Unmap a page obtained by dma_buf_kmap.
> + * @dma_buf:   [in]    buffer to unmap page from.
> + * @page_num:  [in]    page in PAGE_SIZE units to unmap.
> + * @vaddr:     [in]    kernel space pointer obtained from dma_buf_kmap.
> + *
> + * This call must always succeed.
> + */
> +void dma_buf_kunmap(struct dma_buf *dmabuf, unsigned long page_num,
> +                   void *vaddr)
> +{
> +       WARN_ON(!dmabuf);
> +
> +       if (dmabuf->ops->kunmap)
> +               dmabuf->ops->kunmap(dmabuf, page_num, vaddr);
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_kunmap);
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index 24e0f48..ee7ef99 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -50,6 +50,17 @@ struct dma_buf_attachment;
>  * @unmap_dma_buf: decreases usecount of buffer, might deallocate scatter
>  *                pages.
>  * @release: release this buffer; to be called after the last dma_buf_put.
> + * @begin_cpu_access: [optional] called before cpu access to invalidate cpu
> + *                   caches and allocate backing storage (if not yet done)
> + *                   respectively pin the objet into memory.
> + * @end_cpu_access: [optional] called after cpu access to flush cashes.
> + * @kmap_atomic: maps a page from the buffer into kernel address
> + *              space, users may not block until the subsequent unmap call.
> + *              This callback must not sleep.
> + * @kunmap_atomic: [optional] unmaps a atomically mapped page from the buffer.
> + *                This Callback must not sleep.
> + * @kmap: maps a page from the buffer into kernel address space.
> + * @kunmap: [optional] unmaps a page from the buffer.
>  */
>  struct dma_buf_ops {
>        int (*attach)(struct dma_buf *, struct device *,
> @@ -73,6 +84,14 @@ struct dma_buf_ops {
>        /* after final dma_buf_put() */
>        void (*release)(struct dma_buf *);
>
> +       int (*begin_cpu_access)(struct dma_buf *, size_t, size_t,
> +                               enum dma_data_direction);
> +       void (*end_cpu_access)(struct dma_buf *, size_t, size_t,
> +                              enum dma_data_direction);
> +       void *(*kmap_atomic)(struct dma_buf *, unsigned long);
> +       void (*kunmap_atomic)(struct dma_buf *, unsigned long, void *);
> +       void *(*kmap)(struct dma_buf *, unsigned long);
> +       void (*kunmap)(struct dma_buf *, unsigned long, void *);
>  };
>
>  /**
> @@ -140,6 +159,14 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *,
>                                        enum dma_data_direction);
>  void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *,
>                                enum dma_data_direction);
> +int dma_buf_begin_cpu_access(struct dma_buf *dma_buf, size_t start, size_t len,
> +                            enum dma_data_direction dir);
> +void dma_buf_end_cpu_access(struct dma_buf *dma_buf, size_t start, size_t len,
> +                           enum dma_data_direction dir);
> +void *dma_buf_kmap_atomic(struct dma_buf *, unsigned long);
> +void dma_buf_kunmap_atomic(struct dma_buf *, unsigned long, void *);
> +void *dma_buf_kmap(struct dma_buf *, unsigned long);
> +void dma_buf_kunmap(struct dma_buf *, unsigned long, void *);
>  #else
>
>  static inline struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
> @@ -188,6 +215,38 @@ static inline void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
>        return;
>  }
>
> +static inline int dma_buf_begin_cpu_access(struct dma_buf *,
> +                                          size_t, size_t,
> +                                          enum dma_data_direction)
> +{
> +       return -ENODEV;
> +}
> +
> +static inline void dma_buf_end_cpu_access(struct dma_buf *,
> +                                         size_t, size_t,
> +                                         enum dma_data_direction)
> +{
> +}
> +
> +static inline void *dma_buf_kmap_atomic(struct dma_buf *, unsigned long)
> +{
> +       return NULL;
> +}
> +
> +static inline void dma_buf_kunmap_atomic(struct dma_buf *, unsigned long,
> +                                        void *)
> +{
> +}
> +
> +static inline void *dma_buf_kmap(struct dma_buf *, unsigned long)
> +{
> +       return NULL;
> +}
> +
> +static inline void dma_buf_kunmap(struct dma_buf *, unsigned long,
> +                                 void *)
> +{
> +}
>  #endif /* CONFIG_DMA_SHARED_BUFFER */
>
>  #endif /* __DMA_BUF_H__ */
> --
> 1.7.7.5
>
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> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/dri-devel
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