atmel_serial: add DMA support
This patch is based on the DMA-patch by Chip Coldwell for the AT91/AT32 serial USARTS, with some tweaks to make it apply neatly on top of the other patches in this series. The RX and TX code has been moved to a tasklet and reworked a bit. Instead of depending on the ENDRX and TIMEOUT bits in CSR, we simply grab as much data as we can from the DMA buffers. I think this closes a race where the ENDRX bit is set after we read CSR but before we read RPR, although I haven't confirmed this. Similarly, the two TX handlers (ENDTX and TXBUFE) have been combined into one. Since the current code only uses a single TX buffer, there's no point in handling those interrupts separately. This also fixes a DMA sync bug in the original patch. [linux@bohmer.net: rebased onto irq-splitup patch] [hskinnemoen@atmel.com: moved to tasklet, fixed dma bug, misc cleanups] [hskinnemoen@atmel.com: atmel_serial dma: Misc fixes and cleanups] Signed-off-by: Remy Bohmer <linux@bohmer.net> Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com> Cc: Andrew Victor <linux@maxim.org.za> Tested-by: Marc Pignat <marc.pignat@hevs.ch> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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