Re: [Linaro-mm-sig] [PATCH 4/4] staging: android: ion: Support for mapping with dma mapping attributes

Hi Liam,

On Fri, Jan 18, 2019 at 10:37:47AM -0800, Liam Mark wrote:

Add support for configuring dma mapping attributes when mapping and unmapping memory through dma_buf_map_attachment and dma_buf_unmap_attachment.

For example this will allow ION clients to skip cache maintenance, by using DMA_ATTR_SKIP_CPU_SYNC, for buffers which are clean and haven't been accessed by the CPU.

How can a client know that the buffer won't be accessed by the CPU in the future though?

I don't think we can push this decision to clients, because they are lacking information about what else is going on with the buffer. It needs to be done by the exporter, IMO.

Thanks, -Brian

Signed-off-by: Liam Mark lmark@codeaurora.org

drivers/staging/android/ion/ion.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c index 1fe633a7fdba..0aae845b20ba 100644 --- a/drivers/staging/android/ion/ion.c +++ b/drivers/staging/android/ion/ion.c @@ -268,8 +268,8 @@ static struct sg_table *ion_map_dma_buf(struct dma_buf_attachment *attachment, table = a->table; mutex_lock(&buffer->lock);

• if (!dma_map_sg(attachment->dev, table->sgl, table->nents,

• 	direction)) {
  

• if (!dma_map_sg_attrs(attachment->dev, table->sgl, table->nents,

• 	      direction, attachment->dma_map_attrs)) {
  

  mutex_unlock(&buffer->lock); return ERR_PTR(-ENOMEM); }

@@ -287,7 +287,8 @@ static void ion_unmap_dma_buf(struct dma_buf_attachment *attachment, struct ion_buffer *buffer = attachment->dmabuf->priv; mutex_lock(&buffer->lock);

• dma_unmap_sg(attachment->dev, table->sgl, table->nents, direction);

• dma_unmap_sg_attrs(attachment->dev, table->sgl, table->nents, direction,

• 	   attachment->dma_map_attrs);
  

  a->dma_mapped = false; mutex_unlock(&buffer->lock);

}

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