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Implement tty r/w operations using streaming DMA. Goldfish tty for Ranchu platforms has been modified to use streaming DMA mappings for read/write operations. This change eliminates the need for snooping through the TLB in QEMU using cpu_get_phys_page_debug() which does not guarantee that it will return the valid va -> pa mapping. The streaming DMA mapping is implemented using dma_map_single() per transfer, while dma_unmap_single() is used for unmapping right after the DMA transfer. Using DMA API is the proper way for handling r/w transfers and makes this driver more portable, thus effectively eliminating the need for virt_to_page() and page_to_phys() conversions. This change does not affect the old style Goldfish tty behaviour which is still used by the Goldfish emulator. Version register has been added and probed to see which platform is running this driver. Reading from the new register GOLDFISH_TTY_REG_VERSION using the Goldfish emulator will return 0 and driver will work with virtual addresses. Whereas if run on Ranchu it returns 1, and thus DMA is used. (Goldfish and Ranchu are code names for the first and the second generation of virtual boards used by Android emulator.) Signed-off-by: Miodrag Dinic <miodrag.dinic@imgtec.com> Signed-off-by: Goran Ferenc <goran.ferenc@imgtec.com> Signed-off-by: Aleksandar Markovic <aleksandar.markovic@imgtec.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.