UART with no DMA is likely to drop RX characters when system is busy. This is
because the UART interrupt is lower priority than the spi_event GPIO interrupt.
We can work around this by enabling the DMA, so no UART interrupts are required
while recieving, since everything will happen in DMA.
This replaces the other patch(CL 236089) which suggested changing UART IRQ
priority.
BUG=chrome-os-partner:33451
TEST=get firmware to poll the EC for keyboard presses, type really fast on the
keyboard, note how no character is lost anymore
TEST=faft dev mode test now passes, faft is able to type "kbpress $(insert args
for Ctrl+D) 1" correctly without missing characters because firmware is loading
the EC with keyboard polls
TEST=While '+'s are scrolling on the EC terminal paste something big like this:
"kbpress 1 1 1
kbpress 1 1 0
123456789012345678901234567890
". Both kbpresses should be interpreted/executed properly(no "kbprss") and there
should be no missing digits in the echo back.
BRANCH=None
Change-Id: I01d4eaa23f10f07083875846ea48c34da2e2f6ce
Signed-off-by: Alexandru M Stan <amstan@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/236365
Reviewed-by: Randall Spangler <rspangler@chromium.org>
