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111 lines
3.7 KiB
Diff
111 lines
3.7 KiB
Diff
From 379ca7f3ea4501b11779bc6dd6a350873b6ff948 Mon Sep 17 00:00:00 2001
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From: Phil Elwell <phil@raspberrypi.org>
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Date: Fri, 18 May 2018 10:26:59 +0100
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Subject: [PATCH 295/773] sc16is7xx: Fix for "Unexpected interrupt: 8"
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The SC16IS752 has an Enhanced Feature Register which is aliased at the
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same address as the Interrupt Identification Register; accessing it
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requires that a magic value is written to the Line Configuration
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Register. If an interrupt is raised while the EFR is mapped in then
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the ISR won't be able to access the IIR, leading to the "Unexpected
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interrupt" error messages.
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Avoid the problem by claiming a mutex around accesses to the EFR
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register, also claiming the mutex in the interrupt handler work
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item (this is equivalent to disabling interrupts to interlock against
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a non-threaded interrupt handler).
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See: https://github.com/raspberrypi/linux/issues/2529
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Signed-off-by: Phil Elwell <phil@raspberrypi.org>
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---
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drivers/tty/serial/sc16is7xx.c | 28 ++++++++++++++++++++++++++++
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1 file changed, 28 insertions(+)
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--- a/drivers/tty/serial/sc16is7xx.c
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+++ b/drivers/tty/serial/sc16is7xx.c
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@@ -328,6 +328,7 @@ struct sc16is7xx_port {
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struct kthread_worker kworker;
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struct task_struct *kworker_task;
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struct kthread_work irq_work;
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+ struct mutex efr_lock;
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struct sc16is7xx_one p[0];
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};
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@@ -499,6 +500,21 @@ static int sc16is7xx_set_baud(struct uar
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div /= 4;
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}
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+ /* In an amazing feat of design, the Enhanced Features Register shares
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+ * the address of the Interrupt Identification Register, and is
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+ * switched in by writing a magic value (0xbf) to the Line Control
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+ * Register. Any interrupt firing during this time will see the EFR
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+ * where it expects the IIR to be, leading to "Unexpected interrupt"
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+ * messages.
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+ *
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+ * Prevent this possibility by claiming a mutex while accessing the
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+ * EFR, and claiming the same mutex from within the interrupt handler.
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+ * This is similar to disabling the interrupt, but that doesn't work
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+ * because the bulk of the interrupt processing is run as a workqueue
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+ * job in thread context.
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+ */
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+ mutex_lock(&s->efr_lock);
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+
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lcr = sc16is7xx_port_read(port, SC16IS7XX_LCR_REG);
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/* Open the LCR divisors for configuration */
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@@ -514,6 +530,8 @@ static int sc16is7xx_set_baud(struct uar
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/* Put LCR back to the normal mode */
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sc16is7xx_port_write(port, SC16IS7XX_LCR_REG, lcr);
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+ mutex_unlock(&s->efr_lock);
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+
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sc16is7xx_port_update(port, SC16IS7XX_MCR_REG,
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SC16IS7XX_MCR_CLKSEL_BIT,
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prescaler);
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@@ -698,6 +716,8 @@ static void sc16is7xx_ist(struct kthread
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{
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struct sc16is7xx_port *s = to_sc16is7xx_port(ws, irq_work);
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+ mutex_lock(&s->efr_lock);
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+
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while (1) {
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bool keep_polling = false;
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int i;
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@@ -707,6 +727,8 @@ static void sc16is7xx_ist(struct kthread
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if (!keep_polling)
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break;
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}
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+
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+ mutex_unlock(&s->efr_lock);
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}
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static irqreturn_t sc16is7xx_irq(int irq, void *dev_id)
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@@ -901,6 +923,9 @@ static void sc16is7xx_set_termios(struct
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if (!(termios->c_cflag & CREAD))
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port->ignore_status_mask |= SC16IS7XX_LSR_BRK_ERROR_MASK;
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+ /* As above, claim the mutex while accessing the EFR. */
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+ mutex_lock(&s->efr_lock);
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+
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sc16is7xx_port_write(port, SC16IS7XX_LCR_REG,
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SC16IS7XX_LCR_CONF_MODE_B);
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@@ -922,6 +947,8 @@ static void sc16is7xx_set_termios(struct
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/* Update LCR register */
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sc16is7xx_port_write(port, SC16IS7XX_LCR_REG, lcr);
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+ mutex_unlock(&s->efr_lock);
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+
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/* Get baud rate generator configuration */
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baud = uart_get_baud_rate(port, termios, old,
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port->uartclk / 16 / 4 / 0xffff,
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@@ -1187,6 +1214,7 @@ static int sc16is7xx_probe(struct device
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s->regmap = regmap;
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s->devtype = devtype;
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dev_set_drvdata(dev, s);
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+ mutex_init(&s->efr_lock);
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kthread_init_worker(&s->kworker);
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kthread_init_work(&s->irq_work, sc16is7xx_ist);
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