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 /* 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 } 81 EXPORT_SYMBOL_GPL(fsl8250_handle_irq); 82