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

   1// SPDX-License-Identifier: GPL-2.0
   2#if defined(CONFIG_SERIAL_8250_CONSOLE) && defined(CONFIG_MAGIC_SYSRQ)
   3#define SUPPORT_SYSRQ
   4#endif
   5
   6#include <linux/serial_reg.h>
   7#include <linux/serial_8250.h>
   8
   9#include "8250.h"
  10
  11/*
  12 * Freescale 16550 UART "driver", Copyright (C) 2011 Paul Gortmaker.
  13 *
  14 * This isn't a full driver; it just provides an alternate IRQ
  15 * handler to deal with an errata.  Everything else is just
  16 * using the bog standard 8250 support.
  17 *
  18 * We follow code flow of serial8250_default_handle_irq() but add
  19 * a check for a break and insert a dummy read on the Rx for the
  20 * immediately following IRQ event.
  21 *
  22 * We re-use the already existing "bug handling" lsr_saved_flags
  23 * field to carry the "what we just did" information from the one
  24 * IRQ event to the next one.
  25 */
  26
  27int fsl8250_handle_irq(struct uart_port *port)
  28{
  29        unsigned char lsr, orig_lsr;
  30        unsigned long flags;
  31        unsigned int iir;
  32        struct uart_8250_port *up = up_to_u8250p(port);
  33
  34        spin_lock_irqsave(&up->port.lock, flags);
  35
  36        iir = port->serial_in(port, UART_IIR);
  37        if (iir & UART_IIR_NO_INT) {
  38                spin_unlock_irqrestore(&up->port.lock, flags);
  39                return 0;
  40        }
  41
  42        /* This is the WAR; if last event was BRK, then read and return */
  43        if (unlikely(up->lsr_saved_flags & UART_LSR_BI)) {
  44                up->lsr_saved_flags &= ~UART_LSR_BI;
  45                port->serial_in(port, UART_RX);
  46                spin_unlock_irqrestore(&up->port.lock, flags);
  47                return 1;
  48        }
  49
  50        lsr = orig_lsr = up->port.serial_in(&up->port, UART_LSR);
  51
  52        /* Process incoming characters first */
  53        if ((lsr & (UART_LSR_DR | UART_LSR_BI)) &&
  54            (up->ier & (UART_IER_RLSI | UART_IER_RDI))) {
  55                lsr = serial8250_rx_chars(up, lsr);
  56        }
  57
  58        /* Stop processing interrupts on input overrun */
  59        if ((orig_lsr & UART_LSR_OE) && (up->overrun_backoff_time_ms > 0)) {
  60                unsigned long delay;
  61
  62                up->ier = port->serial_in(port, UART_IER);
  63                if (up->ier & (UART_IER_RLSI | UART_IER_RDI)) {
  64                        port->ops->stop_rx(port);
  65                } else {
  66                        /* Keep restarting the timer until
  67                         * the input overrun subsides.
  68                         */
  69                        cancel_delayed_work(&up->overrun_backoff);
  70                }
  71
  72                delay = msecs_to_jiffies(up->overrun_backoff_time_ms);
  73                schedule_delayed_work(&up->overrun_backoff, delay);
  74        }
  75
  76        serial8250_modem_status(up);
  77
  78        if (lsr & UART_LSR_THRE)
  79                serial8250_tx_chars(up);
  80
  81        up->lsr_saved_flags = orig_lsr;
  82        uart_unlock_and_check_sysrq(&up->port, flags);
  83        return 1;
  84}
  85EXPORT_SYMBOL_GPL(fsl8250_handle_irq);
  86