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Some external debuggers do not handle reads/writes from/to DCC on secondary cores. Each core has its own DCC device registers, so when a core reads or writes from/to DCC, it only accesses its own DCC device. Since kernel code can run on any core, every time the kernel wants to write to the console, it might write to a different DCC. In SMP mode, external debugger creates multiple windows, and each window shows the DCC output only from that core's DCC. The result is that console output is either lost or scattered across windows. Selecting this debug option will enable code that serializes all console input and output to core 0. The DCC driver will create input and output FIFOs that all cores will use. Reads and writes from/to DCC are handled by a workqueue that runs only core 0. This is a debug feature to be used only in early stage development where debug serial console support would not be present. It disables PM feature like CPU hotplug and is not suitable for production environment. Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org> Acked-by: Adam Wallis <awallis@codeaurora.org> Signed-off-by: Timur Tabi <timur@codeaurora.org> Signed-off-by: Elliot Berman <eberman@codeaurora.org> Signed-off-by: Sai Prakash Ranjan <quic_saipraka@quicinc.com> Link: https://lore.kernel.org/r/20220428090858.14489-1-quic_saipraka@quicinc.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
302 lines
7.6 KiB
C
302 lines
7.6 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/* Copyright (c) 2010, 2014, 2022 The Linux Foundation. All rights reserved. */
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#include <linux/console.h>
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#include <linux/cpu.h>
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#include <linux/cpumask.h>
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#include <linux/init.h>
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#include <linux/kfifo.h>
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#include <linux/serial.h>
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#include <linux/serial_core.h>
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#include <linux/smp.h>
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#include <linux/spinlock.h>
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#include <asm/dcc.h>
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#include <asm/processor.h>
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#include "hvc_console.h"
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/* DCC Status Bits */
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#define DCC_STATUS_RX (1 << 30)
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#define DCC_STATUS_TX (1 << 29)
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#define DCC_INBUF_SIZE 128
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#define DCC_OUTBUF_SIZE 1024
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/* Lock to serialize access to DCC fifo */
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static DEFINE_SPINLOCK(dcc_lock);
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static DEFINE_KFIFO(inbuf, unsigned char, DCC_INBUF_SIZE);
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static DEFINE_KFIFO(outbuf, unsigned char, DCC_OUTBUF_SIZE);
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static void dcc_uart_console_putchar(struct uart_port *port, unsigned char ch)
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{
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while (__dcc_getstatus() & DCC_STATUS_TX)
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cpu_relax();
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__dcc_putchar(ch);
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}
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static void dcc_early_write(struct console *con, const char *s, unsigned n)
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{
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struct earlycon_device *dev = con->data;
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uart_console_write(&dev->port, s, n, dcc_uart_console_putchar);
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}
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static int __init dcc_early_console_setup(struct earlycon_device *device,
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const char *opt)
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{
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device->con->write = dcc_early_write;
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return 0;
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}
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EARLYCON_DECLARE(dcc, dcc_early_console_setup);
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static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count)
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{
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int i;
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for (i = 0; i < count; i++) {
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while (__dcc_getstatus() & DCC_STATUS_TX)
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cpu_relax();
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__dcc_putchar(buf[i]);
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}
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return count;
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}
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static int hvc_dcc_get_chars(uint32_t vt, char *buf, int count)
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{
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int i;
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for (i = 0; i < count; ++i)
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if (__dcc_getstatus() & DCC_STATUS_RX)
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buf[i] = __dcc_getchar();
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else
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break;
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return i;
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}
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/*
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* Check if the DCC is enabled. If CONFIG_HVC_DCC_SERIALIZE_SMP is enabled,
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* then we assume then this function will be called first on core0. That way,
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* dcc_core0_available will be true only if it's available on core0.
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*/
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static bool hvc_dcc_check(void)
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{
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unsigned long time = jiffies + (HZ / 10);
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static bool dcc_core0_available;
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/*
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* If we're not on core 0, but we previously confirmed that DCC is
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* active, then just return true.
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*/
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int cpu = get_cpu();
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if (IS_ENABLED(CONFIG_HVC_DCC_SERIALIZE_SMP) && cpu && dcc_core0_available) {
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put_cpu();
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return true;
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}
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put_cpu();
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/* Write a test character to check if it is handled */
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__dcc_putchar('\n');
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while (time_is_after_jiffies(time)) {
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if (!(__dcc_getstatus() & DCC_STATUS_TX)) {
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dcc_core0_available = true;
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return true;
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}
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}
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return false;
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}
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/*
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* Workqueue function that writes the output FIFO to the DCC on core 0.
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*/
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static void dcc_put_work(struct work_struct *work)
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{
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unsigned char ch;
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unsigned long irqflags;
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spin_lock_irqsave(&dcc_lock, irqflags);
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/* While there's data in the output FIFO, write it to the DCC */
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while (kfifo_get(&outbuf, &ch))
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hvc_dcc_put_chars(0, &ch, 1);
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/* While we're at it, check for any input characters */
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while (!kfifo_is_full(&inbuf)) {
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if (!hvc_dcc_get_chars(0, &ch, 1))
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break;
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kfifo_put(&inbuf, ch);
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}
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spin_unlock_irqrestore(&dcc_lock, irqflags);
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}
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static DECLARE_WORK(dcc_pwork, dcc_put_work);
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/*
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* Workqueue function that reads characters from DCC and puts them into the
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* input FIFO.
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*/
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static void dcc_get_work(struct work_struct *work)
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{
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unsigned char ch;
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unsigned long irqflags;
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/*
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* Read characters from DCC and put them into the input FIFO, as
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* long as there is room and we have characters to read.
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*/
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spin_lock_irqsave(&dcc_lock, irqflags);
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while (!kfifo_is_full(&inbuf)) {
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if (!hvc_dcc_get_chars(0, &ch, 1))
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break;
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kfifo_put(&inbuf, ch);
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}
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spin_unlock_irqrestore(&dcc_lock, irqflags);
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}
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static DECLARE_WORK(dcc_gwork, dcc_get_work);
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/*
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* Write characters directly to the DCC if we're on core 0 and the FIFO
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* is empty, or write them to the FIFO if we're not.
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*/
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static int hvc_dcc0_put_chars(u32 vt, const char *buf, int count)
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{
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int len;
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unsigned long irqflags;
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if (!IS_ENABLED(CONFIG_HVC_DCC_SERIALIZE_SMP))
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return hvc_dcc_put_chars(vt, buf, count);
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spin_lock_irqsave(&dcc_lock, irqflags);
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if (smp_processor_id() || (!kfifo_is_empty(&outbuf))) {
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len = kfifo_in(&outbuf, buf, count);
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spin_unlock_irqrestore(&dcc_lock, irqflags);
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/*
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* We just push data to the output FIFO, so schedule the
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* workqueue that will actually write that data to DCC.
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* CPU hotplug is disabled in dcc_init so CPU0 cannot be
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* offlined after the cpu online check.
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*/
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if (cpu_online(0))
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schedule_work_on(0, &dcc_pwork);
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return len;
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}
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/*
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* If we're already on core 0, and the FIFO is empty, then just
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* write the data to DCC.
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*/
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len = hvc_dcc_put_chars(vt, buf, count);
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spin_unlock_irqrestore(&dcc_lock, irqflags);
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return len;
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}
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/*
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* Read characters directly from the DCC if we're on core 0 and the FIFO
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* is empty, or read them from the FIFO if we're not.
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*/
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static int hvc_dcc0_get_chars(u32 vt, char *buf, int count)
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{
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int len;
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unsigned long irqflags;
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if (!IS_ENABLED(CONFIG_HVC_DCC_SERIALIZE_SMP))
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return hvc_dcc_get_chars(vt, buf, count);
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spin_lock_irqsave(&dcc_lock, irqflags);
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if (smp_processor_id() || (!kfifo_is_empty(&inbuf))) {
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len = kfifo_out(&inbuf, buf, count);
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spin_unlock_irqrestore(&dcc_lock, irqflags);
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/*
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* If the FIFO was empty, there may be characters in the DCC
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* that we haven't read yet. Schedule a workqueue to fill
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* the input FIFO, so that the next time this function is
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* called, we'll have data. CPU hotplug is disabled in dcc_init
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* so CPU0 cannot be offlined after the cpu online check.
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*/
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if (!len && cpu_online(0))
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schedule_work_on(0, &dcc_gwork);
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return len;
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}
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/*
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* If we're already on core 0, and the FIFO is empty, then just
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* read the data from DCC.
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*/
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len = hvc_dcc_get_chars(vt, buf, count);
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spin_unlock_irqrestore(&dcc_lock, irqflags);
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return len;
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}
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static const struct hv_ops hvc_dcc_get_put_ops = {
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.get_chars = hvc_dcc0_get_chars,
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.put_chars = hvc_dcc0_put_chars,
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};
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static int __init hvc_dcc_console_init(void)
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{
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int ret;
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if (!hvc_dcc_check())
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return -ENODEV;
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/* Returns -1 if error */
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ret = hvc_instantiate(0, 0, &hvc_dcc_get_put_ops);
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return ret < 0 ? -ENODEV : 0;
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}
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console_initcall(hvc_dcc_console_init);
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static int __init hvc_dcc_init(void)
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{
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struct hvc_struct *p;
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if (!hvc_dcc_check())
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return -ENODEV;
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if (IS_ENABLED(CONFIG_HVC_DCC_SERIALIZE_SMP)) {
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pr_warn("\n");
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pr_warn("********************************************************************\n");
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pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n");
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pr_warn("** **\n");
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pr_warn("** HVC_DCC_SERIALIZE_SMP SUPPORT HAS BEEN ENABLED IN THIS KERNEL **\n");
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pr_warn("** **\n");
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pr_warn("** This means that this is a DEBUG kernel and unsafe for **\n");
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pr_warn("** production use and has important feature like CPU hotplug **\n");
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pr_warn("** disabled. **\n");
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pr_warn("** **\n");
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pr_warn("** If you see this message and you are not debugging the **\n");
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pr_warn("** kernel, report this immediately to your vendor! **\n");
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pr_warn("** **\n");
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pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n");
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pr_warn("********************************************************************\n");
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cpu_hotplug_disable();
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}
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p = hvc_alloc(0, 0, &hvc_dcc_get_put_ops, 128);
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return PTR_ERR_OR_ZERO(p);
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}
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device_initcall(hvc_dcc_init);
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