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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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6d7f677a2a
When a serial port gets faulty or gets flooded with inputs, its interrupt handler starts to work double time to get the characters to the workqueue for the tty layer to handle them. When this busy time on the serial/tty subsystem happens during boot, where it is also busy on the userspace trying to initialise, some processes can continuously get preempted and will be on hold until the interrupts subside. The fix is to backoff on processing received characters for a specified amount of time when an input overrun is seen (received a new character before the previous one is processed). This only stops receive and will continue to transmit characters to serial port. After the backoff period is done, it receive will be re-enabled. This is optional and will only be enabled by setting 'overrun-throttle-ms' in the dts. Signed-off-by: Darwin Dingel <darwin.dingel@alliedtelesis.co.nz> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
86 lines
2.3 KiB
C
86 lines
2.3 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#if defined(CONFIG_SERIAL_8250_CONSOLE) && defined(CONFIG_MAGIC_SYSRQ)
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#define SUPPORT_SYSRQ
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#endif
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#include <linux/serial_reg.h>
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#include <linux/serial_8250.h>
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#include "8250.h"
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/*
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* Freescale 16550 UART "driver", Copyright (C) 2011 Paul Gortmaker.
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*
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* This isn't a full driver; it just provides an alternate IRQ
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* handler to deal with an errata. Everything else is just
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* using the bog standard 8250 support.
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*
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* We follow code flow of serial8250_default_handle_irq() but add
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* a check for a break and insert a dummy read on the Rx for the
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* immediately following IRQ event.
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*
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* We re-use the already existing "bug handling" lsr_saved_flags
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* field to carry the "what we just did" information from the one
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* IRQ event to the next one.
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*/
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int fsl8250_handle_irq(struct uart_port *port)
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{
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unsigned char lsr, orig_lsr;
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unsigned long flags;
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unsigned int iir;
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struct uart_8250_port *up = up_to_u8250p(port);
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spin_lock_irqsave(&up->port.lock, flags);
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iir = port->serial_in(port, UART_IIR);
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if (iir & UART_IIR_NO_INT) {
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spin_unlock_irqrestore(&up->port.lock, flags);
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return 0;
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}
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/* This is the WAR; if last event was BRK, then read and return */
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if (unlikely(up->lsr_saved_flags & UART_LSR_BI)) {
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up->lsr_saved_flags &= ~UART_LSR_BI;
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port->serial_in(port, UART_RX);
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spin_unlock_irqrestore(&up->port.lock, flags);
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return 1;
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}
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lsr = orig_lsr = up->port.serial_in(&up->port, UART_LSR);
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/* Process incoming characters first */
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if ((lsr & (UART_LSR_DR | UART_LSR_BI)) &&
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(up->ier & (UART_IER_RLSI | UART_IER_RDI))) {
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lsr = serial8250_rx_chars(up, lsr);
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}
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/* Stop processing interrupts on input overrun */
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if ((orig_lsr & UART_LSR_OE) && (up->overrun_backoff_time_ms > 0)) {
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unsigned long delay;
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up->ier = port->serial_in(port, UART_IER);
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if (up->ier & (UART_IER_RLSI | UART_IER_RDI)) {
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port->ops->stop_rx(port);
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} else {
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/* Keep restarting the timer until
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* the input overrun subsides.
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*/
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cancel_delayed_work(&up->overrun_backoff);
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}
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delay = msecs_to_jiffies(up->overrun_backoff_time_ms);
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schedule_delayed_work(&up->overrun_backoff, delay);
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}
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serial8250_modem_status(up);
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if (lsr & UART_LSR_THRE)
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serial8250_tx_chars(up);
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up->lsr_saved_flags = orig_lsr;
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uart_unlock_and_check_sysrq(&up->port, flags);
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return 1;
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}
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EXPORT_SYMBOL_GPL(fsl8250_handle_irq);
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