serial: samsung: add DMA support for TX

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Add TX DMA transfers support for samsung serial driver. It's enabled
when "dmas" property is defined in serial device-tree node, otherwise
TX transfers are prerformed using PIO.

TX DMA is used for data segments larger than fifosize to reduce number
of interrupts during data transmission. For buffers shorter than fifosize
PIO mode is selected.

Data blocks for DMA transfers are aligned to cache line size to avoid
problems with coherency (some areas of TX circ buffer can be used by
CPU during DMA transaction, so we have to ensure that our data is always
consistent).

Based on previous work of Sylwester Nawrocki and Lukasz Czerwinski.

Signed-off-by: Robert Baldyga <r.baldyga@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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Robert Baldyga 2014-12-10 12:49:26 +01:00 • committed by Greg Kroah-Hartman

parent 62c37eedb7

commit 29bef79908

2 changed files with 225 additions and 16 deletions

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238

drivers/tty/serial/samsung.c

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3

drivers/tty/serial/samsung.h

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