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This patch adds the command buffer (CB) module, which allows the user to create and destroy CBs and to map them to the user's process address-space. A command buffer is a memory blocks that reside in DMA-able address-space and is physically contiguous so it can be accessed by the device without MMU translation. The command buffer memory is allocated using the coherent DMA API. When creating a new CB, the IOCTL returns a handle of it, and the user-space process needs to use that handle to mmap the buffer to get a VA in the user's address-space. Before destroying (freeing) a CB, the user must unmap the CB's VA using the CB handle. Each CB has a reference counter, which tracks its usage in command submissions and also its mmaps (only a single mmap is allowed). The driver maintains a pool of pre-allocated CBs in order to reduce latency during command submissions. In case the pool is empty, the driver will go to the slow-path of allocating a new CB, i.e. calling dma_alloc_coherent. Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.