1 // SPDX-License-Identifier: GPL-2.0
2 #include <linux/serial_reg.h>
3 #include <linux/serial_8250.h>
4
5 #include "8250.h"
6
7 /*
8 * Freescale 16550 UART "driver", Copyright (C) 2011 Paul Gortmaker.
9 *
10 * This isn't a full driver; it just provides an alternate IRQ
11 * handler to deal with an errata. Everything else is just
12 * using the bog standard 8250 support.
13 *
14 * We follow code flow of serial8250_default_handle_irq() but add
15 * a check for a break and insert a dummy read on the Rx for the
16 * immediately following IRQ event.
17 *
18 * We re-use the already existing "bug handling" lsr_saved_flags
19 * field to carry the "what we just did" information from the one
20 * IRQ event to the next one.
21 */
22
fsl8250_handle_irq(struct uart_port * port)23 int fsl8250_handle_irq(struct uart_port *port)
24 {
25 unsigned char lsr, orig_lsr;
26 unsigned long flags;
27 unsigned int iir;
28 struct uart_8250_port *up = up_to_u8250p(port);
29
30 spin_lock_irqsave(&up->port.lock, flags);
31
32 iir = port->serial_in(port, UART_IIR);
33 if (iir & UART_IIR_NO_INT) {
34 spin_unlock_irqrestore(&up->port.lock, flags);
35 return 0;
36 }
37
38 /* This is the WAR; if last event was BRK, then read and return */
39 if (unlikely(up->lsr_saved_flags & UART_LSR_BI)) {
40 up->lsr_saved_flags &= ~UART_LSR_BI;
41 port->serial_in(port, UART_RX);
42 spin_unlock_irqrestore(&up->port.lock, flags);
43 return 1;
44 }
45
46 lsr = orig_lsr = up->port.serial_in(&up->port, UART_LSR);
47
48 if (lsr & (UART_LSR_DR | UART_LSR_BI))
49 lsr = serial8250_rx_chars(up, lsr);
50
51 serial8250_modem_status(up);
52
53 if (lsr & UART_LSR_THRE)
54 serial8250_tx_chars(up);
55
56 up->lsr_saved_flags = orig_lsr;
57 spin_unlock_irqrestore(&up->port.lock, flags);
58 return 1;
59 }
60 EXPORT_SYMBOL_GPL(fsl8250_handle_irq);
61
