// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2010, 2014, 2022 The Linux Foundation. All rights reserved. */
#include <linux/console.h>
#include <linux/cpu.h>
#include <linux/cpumask.h>
#include <linux/init.h>
#include <linux/kfifo.h>
#include <linux/serial.h>
#include <linux/serial_core.h>
#include <linux/smp.h>
#include <linux/spinlock.h>
#include <asm/dcc.h>
#include <asm/processor.h>
#include "hvc_console.h"
/* DCC Status Bits */
#define DCC_STATUS_RX (1 << 30)
#define DCC_STATUS_TX (1 << 29)
#define DCC_INBUF_SIZE 128
#define DCC_OUTBUF_SIZE 1024
/* Lock to serialize access to DCC fifo */
static DEFINE_SPINLOCK(dcc_lock);
static DEFINE_KFIFO(inbuf, u8, DCC_INBUF_SIZE);
static DEFINE_KFIFO(outbuf, u8, DCC_OUTBUF_SIZE);
static void dcc_uart_console_putchar(struct uart_port *port, u8 ch)
{
while (__dcc_getstatus() & DCC_STATUS_TX)
cpu_relax();
__dcc_putchar(ch);
}
static void dcc_early_write(struct console *con, const char *s, unsigned n)
{
struct earlycon_device *dev = con->data;
uart_console_write(&dev->port, s, n, dcc_uart_console_putchar);
}
static int __init dcc_early_console_setup(struct earlycon_device *device,
const char *opt)
{
unsigned int count = 0x4000000;
while (--count && (__dcc_getstatus() & DCC_STATUS_TX))
cpu_relax();
if (__dcc_getstatus() & DCC_STATUS_TX)
return -ENODEV;
device->con->write = dcc_early_write;
return 0;
}
EARLYCON_DECLARE(dcc, dcc_early_console_setup);
static ssize_t hvc_dcc_put_chars(uint32_t vt, const u8 *buf, size_t count)
{
size_t i;
for (i = 0; i < count; i++) {
while (__dcc_getstatus() & DCC_STATUS_TX)
cpu_relax();
__dcc_putchar(buf[i]);
}
return count;
}
static ssize_t hvc_dcc_get_chars(uint32_t vt, u8 *buf, size_t count)
{
size_t i;
for (i = 0; i < count; ++i)
if (__dcc_getstatus() & DCC_STATUS_RX)
buf[i] = __dcc_getchar();
else
break;
return i;
}
/*
* Check if the DCC is enabled. If CONFIG_HVC_DCC_SERIALIZE_SMP is enabled,
* then we assume then this function will be called first on core0. That way,
* dcc_core0_available will be true only if it's available on core0.
*/
static bool hvc_dcc_check(void)
{
unsigned long time = jiffies + (HZ / 10);
static bool dcc_core0_available;
/*
* If we're not on core 0, but we previously confirmed that DCC is
* active, then just return true.
*/
int cpu = get_cpu();
if (IS_ENABLED(CONFIG_HVC_DCC_SERIALIZE_SMP) && cpu && dcc_core0_available) {
put_cpu();
return true;
}
put_cpu();
/* Write a test character to check if it is handled */
__dcc_putchar('\n');
while (time_is_after_jiffies(time)) {
if (!(__dcc_getstatus() & DCC_STATUS_TX)) {
dcc_core0_available = true;
return true;
}
}
return false;
}
/*
* Workqueue function that writes the output FIFO to the DCC on core 0.
*/
static void dcc_put_work(struct work_struct *work)
{
unsigned char ch;
unsigned long irqflags;
spin_lock_irqsave(&dcc_lock, irqflags);
/* While there's data in the output FIFO, write it to the DCC */
while (kfifo_get(&outbuf, &ch))
hvc_dcc_put_chars(0, &ch, 1);
/* While we're at it, check for any input characters */
while (!kfifo_is_full(&inbuf)) {
if (!hvc_dcc_get_chars(0, &ch, 1))
break;
kfifo_put(&inbuf, ch);
}
spin_unlock_irqrestore(&dcc_lock, irqflags);
}
static DECLARE_WORK(dcc_pwork, dcc_put_work);
/*
* Workqueue function that reads characters from DCC and puts them into the
* input FIFO.
*/
static void dcc_get_work(struct work_struct *work)
{
unsigned long irqflags;
u8 ch;
/*
* Read characters from DCC and put them into the input FIFO, as
* long as there is room and we have characters to read.
*/
spin_lock_irqsave(&dcc_lock, irqflags);
while (!kfifo_is_full(&inbuf)) {
if (!hvc_dcc_get_chars(0, &ch, 1))
break;
kfifo_put(&inbuf, ch);
}
spin_unlock_irqrestore(&dcc_lock, irqflags);
}
static DECLARE_WORK(dcc_gwork, dcc_get_work);
/*
* Write characters directly to the DCC if we're on core 0 and the FIFO
* is empty, or write them to the FIFO if we're not.
*/
static ssize_t hvc_dcc0_put_chars(u32 vt, const u8 *buf, size_t count)
{
unsigned long irqflags;
ssize_t len;
if (!IS_ENABLED(CONFIG_HVC_DCC_SERIALIZE_SMP))
return hvc_dcc_put_chars(vt, buf, count);
spin_lock_irqsave(&dcc_lock, irqflags);
if (smp_processor_id() || (!kfifo_is_empty(&outbuf))) {
len = kfifo_in(&outbuf, buf, count);
spin_unlock_irqrestore(&dcc_lock, irqflags);
/*
* We just push data to the output FIFO, so schedule the
* workqueue that will actually write that data to DCC.
* CPU hotplug is disabled in dcc_init so CPU0 cannot be
* offlined after the cpu online check.
*/
if (cpu_online(0))
schedule_work_on(0, &dcc_pwork);
return len;
}
/*
* If we're already on core 0, and the FIFO is empty, then just
* write the data to DCC.
*/
len = hvc_dcc_put_chars(vt, buf, count);
spin_unlock_irqrestore(&dcc_lock, irqflags);
return len;
}
/*
* Read characters directly from the DCC if we're on core 0 and the FIFO
* is empty, or read them from the FIFO if we're not.
*/
static ssize_t hvc_dcc0_get_chars(u32 vt, u8 *buf, size_t count)
{
unsigned long irqflags;
ssize_t len;
if (!IS_ENABLED(CONFIG_HVC_DCC_SERIALIZE_SMP))
return hvc_dcc_get_chars(vt, buf, count);
spin_lock_irqsave(&dcc_lock, irqflags);
if (smp_processor_id() || (!kfifo_is_empty(&inbuf))) {
len = kfifo_out(&inbuf, buf, count);
spin_unlock_irqrestore(&dcc_lock, irqflags);
/*
* If the FIFO was empty, there may be characters in the DCC
* that we haven't read yet. Schedule a workqueue to fill
* the input FIFO, so that the next time this function is
* called, we'll have data. CPU hotplug is disabled in dcc_init
* so CPU0 cannot be offlined after the cpu online check.
*/
if (!len && cpu_online(0))
schedule_work_on(0, &dcc_gwork);
return len;
}
/*
* If we're already on core 0, and the FIFO is empty, then just
* read the data from DCC.
*/
len = hvc_dcc_get_chars(vt, buf, count);
spin_unlock_irqrestore(&dcc_lock, irqflags);
return len;
}
static const struct hv_ops hvc_dcc_get_put_ops = {
.get_chars = hvc_dcc0_get_chars,
.put_chars = hvc_dcc0_put_chars,
};
static int __init hvc_dcc_console_init(void)
{
int ret;
if (!hvc_dcc_check())
return -ENODEV;
/* Returns -1 if error */
ret = hvc_instantiate(0, 0, &hvc_dcc_get_put_ops);
return ret < 0 ? -ENODEV : 0;
}
console_initcall(hvc_dcc_console_init);
static int __init hvc_dcc_init(void)
{
struct hvc_struct *p;
if (!hvc_dcc_check())
return -ENODEV;
if (IS_ENABLED(CONFIG_HVC_DCC_SERIALIZE_SMP)) {
pr_warn("\n");
pr_warn("********************************************************************\n");
pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n");
pr_warn("** **\n");
pr_warn("** HVC_DCC_SERIALIZE_SMP SUPPORT HAS BEEN ENABLED IN THIS KERNEL **\n");
pr_warn("** **\n");
pr_warn("** This means that this is a DEBUG kernel and unsafe for **\n");
pr_warn("** production use and has important feature like CPU hotplug **\n");
pr_warn("** disabled. **\n");
pr_warn("** **\n");
pr_warn("** If you see this message and you are not debugging the **\n");
pr_warn("** kernel, report this immediately to your vendor! **\n");
pr_warn("** **\n");
pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n");
pr_warn("********************************************************************\n");
cpu_hotplug_disable();
}
p = hvc_alloc(0, 0, &hvc_dcc_get_put_ops, 128);
return PTR_ERR_OR_ZERO(p);
}
device_initcall(hvc_dcc_init);
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