tty/serial: atmel: RS485 & ISO7816: wait for TXRDY before sending data

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At this moment, TXEMPTY is checked before sending data on RS485 and ISO7816
modes. However, TXEMPTY is risen when FIFO (if used) or the Transmit Shift
Register are empty, even though TXRDY might be up and controller is able to
receive data. Since the controller sends data only when TXEMPTY is ready,
on RS485, when DMA is not used, the RTS pin is driven low after each byte.
With this patch, the characters will be transmitted when TXRDY is up and
so, RTS pin will remain high between bytes.
The performance improvement on RS485 is about 8% with a baudrate of 300.

Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
Acked-by: Richard Genoud <richard.genoud@gmail.com>
Link: https://lore.kernel.org/r/20200107111656.26308-1-codrin.ciubotariu@microchip.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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Codrin.Ciubotariu@microchip.com 2020-01-07 11:17:47 +00:00 • committed by Greg Kroah-Hartman

parent 8e20fc3917

commit 477b838310

1 changed files with 19 additions and 7 deletions

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drivers/tty/serial/atmel_serial.c

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