How create an ION buffer to be accessible by kernel

[michael s]

Hi,

In my user space application, I allocate a buffer using
ion_alloc() and ion_map().

I am able to pass the map_fd (file descriptor return from ion_map() to my driver.
And in my driver, I get a dma_buf using dma_buf_get().

 struct dma_buf *dbuf = dma_buf_get(fd);

My question is how can I map this dma_buf to my kernel address space so that my driver code can access (read/write) this buffer?
I think I need to use dma_buf_kmap.
But what should I pass to the 2nd parameter of dma_buf_kmap, the api specified the 2nd parameter is (the page in
PAGE_SIZE units to map) dma_buf_kmap?

https://www.kernel.org/doc/htmldocs/device-drivers/API-dma-buf-kmap.html
 

I want the whole dma_buf to be accessible.

[alexandre bailon]

Hi,

I haven't good knowledge about dma_buf but I don't think you can use ion file descriptor to get a dma_buf.

To access map an ION buffer allocated from user space, you should use:

struct ion_handle *ion_import_fd(struct ion_client *client, int fd) and

void *ion_map_kernel(struct ion_client *client, struct ion_handle *handle)

The first function will convert the ion fd in in struct ion_handle. The second function will use the ion_handle to map the buffer.

Regards

[m silverstri]

Thanks.

Do you know how to answer my original question:

But what should I pass to the 2nd parameter of dma_buf_kmap, the api
specified the 2nd parameter is (the page in
PAGE_SIZE units to map) dma_buf_kmap?

https://www.kernel.org/doc/htmldocs/device-drivers/API-dma-buf-kmap.html

Thank you.

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