drivers/tty/serial/8250/8250_fsl.c

   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
  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);