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linux-next/include/linux/serial_8250.h
Andy Shevchenko bedb404e91 serial: 8250_port: Don't use power management for kernel console 
Doing any kind of power management for kernel console is really bad idea.

First of all, it runs in poll and atomic mode. This fact attaches a limitation
on the functions that might be called. For example, pm_runtime_get_sync() might
sleep and thus can't be used. This call needs, for example, to bring the device
to powered on state on the system, where the power on sequence may require
on-atomic operations, such as Intel Cherrytrail with ACPI enumerated UARTs.
That said, on ACPI enabled platforms it might even call firmware for a job.

On the other hand pm_runtime_get() doesn't guarantee that device will become
powered on fast enough.

Besides that, imagine the case when console is about to print a kernel Oops and
it's powered off. In such an emergency case calling the complex functions is
not the best what we can do, taking into consideration that user wants to see
at least something of the last kernel word before it passes away.

Here we modify the 8250 console code to prevent runtime power management.

Note, there is a behaviour change for OMAP boards. It will require to detach
kernel console to become idle.

Link: https://lists.openwall.net/linux-kernel/2018/09/29/65
Suggested-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200217114016.49856-6-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-17 15:58:00 +01:00

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/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
* linux/include/linux/serial_8250.h
*
* Copyright (C) 2004 Russell King
*/
#ifndef _LINUX_SERIAL_8250_H
#define _LINUX_SERIAL_8250_H
#include <linux/serial_core.h>
#include <linux/serial_reg.h>
#include <linux/platform_device.h>
/*
* This is the platform device platform_data structure
*/
struct plat_serial8250_port {
unsigned long iobase; /* io base address */
void __iomem *membase; /* ioremap cookie or NULL */
resource_size_t mapbase; /* resource base */
unsigned int irq; /* interrupt number */
unsigned long irqflags; /* request_irq flags */
unsigned int uartclk; /* UART clock rate */
void *private_data;
unsigned char regshift; /* register shift */
unsigned char iotype; /* UPIO_* */
unsigned char hub6;
unsigned char has_sysrq; /* supports magic SysRq */
upf_t flags; /* UPF_* flags */
unsigned int type; /* If UPF_FIXED_TYPE */
unsigned int (*serial_in)(struct uart_port *, int);
void (*serial_out)(struct uart_port *, int, int);
void (*set_termios)(struct uart_port *,
struct ktermios *new,
struct ktermios *old);
void (*set_ldisc)(struct uart_port *,
struct ktermios *);
unsigned int (*get_mctrl)(struct uart_port *);
int (*handle_irq)(struct uart_port *);
void (*pm)(struct uart_port *, unsigned int state,
unsigned old);
void (*handle_break)(struct uart_port *);
};
/*
* Allocate 8250 platform device IDs. Nothing is implied by
* the numbering here, except for the legacy entry being -1.
*/
enum {
PLAT8250_DEV_LEGACY = -1,
PLAT8250_DEV_PLATFORM,
PLAT8250_DEV_PLATFORM1,
PLAT8250_DEV_PLATFORM2,
PLAT8250_DEV_FOURPORT,
PLAT8250_DEV_ACCENT,
PLAT8250_DEV_BOCA,
PLAT8250_DEV_EXAR_ST16C554,
PLAT8250_DEV_HUB6,
PLAT8250_DEV_AU1X00,
PLAT8250_DEV_SM501,
};
struct uart_8250_dma;
struct uart_8250_port;
/**
* 8250 core driver operations
*
* @setup_irq() Setup irq handling. The universal 8250 driver links this
* port to the irq chain. Other drivers may @request_irq().
* @release_irq() Undo irq handling. The universal 8250 driver unlinks
* the port from the irq chain.
*/
struct uart_8250_ops {
int (*setup_irq)(struct uart_8250_port *);
void (*release_irq)(struct uart_8250_port *);
};
struct uart_8250_em485 {
struct hrtimer start_tx_timer; /* "rs485 start tx" timer */
struct hrtimer stop_tx_timer; /* "rs485 stop tx" timer */
struct hrtimer *active_timer; /* pointer to active timer */
struct uart_8250_port *port; /* for hrtimer callbacks */
unsigned int tx_stopped:1; /* tx is currently stopped */
};
/*
* This should be used by drivers which want to register
* their own 8250 ports without registering their own
* platform device. Using these will make your driver
* dependent on the 8250 driver.
*/
struct uart_8250_port {
struct uart_port port;
struct timer_list timer; /* "no irq" timer */
struct list_head list; /* ports on this IRQ */
u32 capabilities; /* port capabilities */
unsigned short bugs; /* port bugs */
bool fifo_bug; /* min RX trigger if enabled */
unsigned int tx_loadsz; /* transmit fifo load size */
unsigned char acr;
unsigned char fcr;
unsigned char ier;
unsigned char lcr;
unsigned char mcr;
unsigned char mcr_mask; /* mask of user bits */
unsigned char mcr_force; /* mask of forced bits */
unsigned char cur_iotype; /* Running I/O type */
unsigned int rpm_tx_active;
unsigned char canary; /* non-zero during system sleep
* if no_console_suspend
*/
unsigned char probe;
struct mctrl_gpios *gpios;
#define UART_PROBE_RSA (1 << 0)
/*
* Some bits in registers are cleared on a read, so they must
* be saved whenever the register is read but the bits will not
* be immediately processed.
*/
#define LSR_SAVE_FLAGS UART_LSR_BRK_ERROR_BITS
unsigned char lsr_saved_flags;
#define MSR_SAVE_FLAGS UART_MSR_ANY_DELTA
unsigned char msr_saved_flags;
struct uart_8250_dma *dma;
const struct uart_8250_ops *ops;
/* 8250 specific callbacks */
int (*dl_read)(struct uart_8250_port *);
void (*dl_write)(struct uart_8250_port *, int);
struct uart_8250_em485 *em485;
void (*rs485_start_tx)(struct uart_8250_port *);
void (*rs485_stop_tx)(struct uart_8250_port *);
/* Serial port overrun backoff */
struct delayed_work overrun_backoff;
u32 overrun_backoff_time_ms;
};
static inline struct uart_8250_port *up_to_u8250p(struct uart_port *up)
{
return container_of(up, struct uart_8250_port, port);
}
int serial8250_register_8250_port(struct uart_8250_port *);
void serial8250_unregister_port(int line);
void serial8250_suspend_port(int line);
void serial8250_resume_port(int line);
extern int early_serial_setup(struct uart_port *port);
extern int early_serial8250_setup(struct earlycon_device *device,
const char *options);
extern void serial8250_do_set_termios(struct uart_port *port,
struct ktermios *termios, struct ktermios *old);
extern void serial8250_do_set_ldisc(struct uart_port *port,
struct ktermios *termios);
extern unsigned int serial8250_do_get_mctrl(struct uart_port *port);
extern int serial8250_do_startup(struct uart_port *port);
extern void serial8250_do_shutdown(struct uart_port *port);
extern void serial8250_do_pm(struct uart_port *port, unsigned int state,
unsigned int oldstate);
extern void serial8250_do_set_mctrl(struct uart_port *port, unsigned int mctrl);
extern void serial8250_do_set_divisor(struct uart_port *port, unsigned int baud,
unsigned int quot,
unsigned int quot_frac);
extern int fsl8250_handle_irq(struct uart_port *port);
int serial8250_handle_irq(struct uart_port *port, unsigned int iir);
unsigned char serial8250_rx_chars(struct uart_8250_port *up, unsigned char lsr);
void serial8250_read_char(struct uart_8250_port *up, unsigned char lsr);
void serial8250_tx_chars(struct uart_8250_port *up);
unsigned int serial8250_modem_status(struct uart_8250_port *up);
void serial8250_init_port(struct uart_8250_port *up);
void serial8250_set_defaults(struct uart_8250_port *up);
void serial8250_console_write(struct uart_8250_port *up, const char *s,
unsigned int count);
int serial8250_console_setup(struct uart_port *port, char *options, bool probe);
int serial8250_console_exit(struct uart_port *port);
extern void serial8250_set_isa_configurator(void (*v)
(int port, struct uart_port *up,
u32 *capabilities));
#endif
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