LXR linux/drivers/tty/serial/8250/8250

   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
  23int 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        /* Process incoming characters first */
  49        if ((lsr & (UART_LSR_DR | UART_LSR_BI)) &&
  50            (up->ier & (UART_IER_RLSI | UART_IER_RDI))) {
  51                lsr = serial8250_rx_chars(up, lsr);
  52        }
  53
  54        /* Stop processing interrupts on input overrun */
  55        if ((orig_lsr & UART_LSR_OE) && (up->overrun_backoff_time_ms > 0)) {
  56                unsigned long delay;
  57
  58                up->ier = port->serial_in(port, UART_IER);
  59                if (up->ier & (UART_IER_RLSI | UART_IER_RDI)) {
  60                        port->ops->stop_rx(port);
  61                } else {
  62                        /* Keep restarting the timer until
  63                         * the input overrun subsides.
  64                         */
  65                        cancel_delayed_work(&up->overrun_backoff);
  66                }
  67
  68                delay = msecs_to_jiffies(up->overrun_backoff_time_ms);
  69                schedule_delayed_work(&up->overrun_backoff, delay);
  70        }
  71
  72        serial8250_modem_status(up);
  73
  74        if (lsr & UART_LSR_THRE)
  75                serial8250_tx_chars(up);
  76
  77        up->lsr_saved_flags = orig_lsr;
  78        uart_unlock_and_check_sysrq(&up->port, flags);
  79        return 1;
  80}
  81EXPORT_SYMBOL_GPL(fsl8250_handle_irq);
  82