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From fc4fafeed9a7cc89b4779681f046a8cc0f506dd9 Mon Sep 17 00:00:00 2001
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From: Phil Elwell <phil@raspberrypi.org>
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Date: Wed, 11 Oct 2017 13:48:04 +0100
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Subject: [PATCH 123/454] amba-pl011: Report AUTOCTS capability to framework
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The PL011 has full hardware RTS/CTS support which is enabled by
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the driver when flow control is requested. However, it doesn't
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notify the UART framework of the fact, causing the software CTS
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support to be enabled at the same time.
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Software CTS triggers the sending of another batch of characters
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when CTS becomes asserted. The pl011 interrupt handler processes
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the CTIS bit before TXIS, which can cause some characters to be
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sent between the time that the TXIS bit first becomes asserted
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and the time it is handled by a call to px011_tx_chars. This
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would be fine were it not for the optimisation in pl011_tx_char
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that assumes the FIFO is half-empty if called from the interrupt
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handler and skips the checking of the FIFO status register before
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sending each character, leading to data loss if the FIFO is more
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than half-full.
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Prevent the data loss and improve efficiency by indicating the
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AUTOCTS support.
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Signed-off-by: Phil Elwell <phil@raspberrypi.org>
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---
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drivers/tty/serial/amba-pl011.c | 2 ++
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1 file changed, 2 insertions(+)
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--- a/drivers/tty/serial/amba-pl011.c
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+++ b/drivers/tty/serial/amba-pl011.c
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@@ -2061,9 +2061,11 @@ pl011_set_termios(struct uart_port *port
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old_cr |= UART011_CR_CTSEN;
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uap->autorts = true;
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+ port->status |= UPSTAT_AUTOCTS;
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} else {
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old_cr &= ~(UART011_CR_CTSEN | UART011_CR_RTSEN);
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uap->autorts = false;
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+ port->status &= ~UPSTAT_AUTOCTS;
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}
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if (uap->vendor->oversampling) {
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