// SPDX-License-Identifier: GPL-2.0
-/* Copyright (c) 2010, 2014 The Linux Foundation. All rights reserved. */
+/* 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>
#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, unsigned char, DCC_INBUF_SIZE);
+static DEFINE_KFIFO(outbuf, unsigned char, DCC_OUTBUF_SIZE);
+
static void dcc_uart_console_putchar(struct uart_port *port, unsigned char ch)
{
while (__dcc_getstatus() & DCC_STATUS_TX)
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))
+ 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 char ch;
+ unsigned long irqflags;
+
+ /*
+ * 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 int hvc_dcc0_put_chars(u32 vt, const char *buf, int count)
+{
+ int len;
+ unsigned long irqflags;
+
+ 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 int hvc_dcc0_get_chars(u32 vt, char *buf, int count)
+{
+ int len;
+ unsigned long irqflags;
+
+ 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_dcc_get_chars,
- .put_chars = hvc_dcc_put_chars,
+ .get_chars = hvc_dcc0_get_chars,
+ .put_chars = hvc_dcc0_put_chars,
};
static int __init hvc_dcc_console_init(void)
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);
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