target/linux/brcm2708/patches-4.14/950-0311-sc16is7xx-Fix-for-Unexpected-interrupt-8.patch

   1 From d4601b298709e44a998df772ac1c85707603fde4 Mon Sep 17 00:00:00 2001
   2 From: Phil Elwell <phil@raspberrypi.org>
   3 Date: Fri, 18 May 2018 10:26:59 +0100
   4 Subject: [PATCH 311/454] sc16is7xx: Fix for "Unexpected interrupt: 8"
   5
   6 The SC16IS752 has an Enhanced Feature Register which is aliased at the
   7 same address as the Interrupt Identification Register; accessing it
   8 requires that a magic value is written to the Line Configuration
   9 Register. If an interrupt is raised while the EFR is mapped in then
  10 the ISR won't be able to access the IIR, leading to the "Unexpected
  11 interrupt" error messages.
  12
  13 Avoid the problem by claiming a mutex around accesses to the EFR
  14 register, also claiming the mutex in the interrupt handler work
  15 item (this is equivalent to disabling interrupts to interlock against
  16 a non-threaded interrupt handler).
  17
  18 See: https://github.com/raspberrypi/linux/issues/2529
  19
  20 Signed-off-by: Phil Elwell <phil@raspberrypi.org>
  21 ---
  22  drivers/tty/serial/sc16is7xx.c | 28 ++++++++++++++++++++++++++++
  23  1 file changed, 28 insertions(+)
  24
  25 --- a/drivers/tty/serial/sc16is7xx.c
  26 +++ b/drivers/tty/serial/sc16is7xx.c
  27 @@ -333,6 +333,7 @@ struct sc16is7xx_port {
  28         struct kthread_worker           kworker;
  29         struct task_struct              *kworker_task;
  30         struct kthread_work             irq_work;
  31 +       struct mutex                    efr_lock;
  32         struct sc16is7xx_one            p[0];
  33  };
  34
  35 @@ -504,6 +505,21 @@ static int sc16is7xx_set_baud(struct uar
  36                 div /= 4;
  37         }
  38
  39 +       /* In an amazing feat of design, the Enhanced Features Register shares
  40 +        * the address of the Interrupt Identification Register, and is
  41 +        * switched in by writing a magic value (0xbf) to the Line Control
  42 +        * Register. Any interrupt firing during this time will see the EFR
  43 +        * where it expects the IIR to be, leading to "Unexpected interrupt"
  44 +        * messages.
  45 +        *
  46 +        * Prevent this possibility by claiming a mutex while accessing the
  47 +        * EFR, and claiming the same mutex from within the interrupt handler.
  48 +        * This is similar to disabling the interrupt, but that doesn't work
  49 +        * because the bulk of the interrupt processing is run as a workqueue
  50 +        * job in thread context.
  51 +        */
  52 +       mutex_lock(&s->efr_lock);
  53 +
  54         lcr = sc16is7xx_port_read(port, SC16IS7XX_LCR_REG);
  55
  56         /* Open the LCR divisors for configuration */
  57 @@ -519,6 +535,8 @@ static int sc16is7xx_set_baud(struct uar
  58         /* Put LCR back to the normal mode */
  59         sc16is7xx_port_write(port, SC16IS7XX_LCR_REG, lcr);
  60
  61 +       mutex_unlock(&s->efr_lock);
  62 +
  63         sc16is7xx_port_update(port, SC16IS7XX_MCR_REG,
  64                               SC16IS7XX_MCR_CLKSEL_BIT,
  65                               prescaler);
  66 @@ -701,6 +719,8 @@ static void sc16is7xx_ist(struct kthread
  67  {
  68         struct sc16is7xx_port *s = to_sc16is7xx_port(ws, irq_work);
  69
  70 +       mutex_lock(&s->efr_lock);
  71 +
  72         while (1) {
  73                 bool keep_polling = false;
  74                 int i;
  75 @@ -710,6 +730,8 @@ static void sc16is7xx_ist(struct kthread
  76                 if (!keep_polling)
  77                         break;
  78         }
  79 +
  80 +       mutex_unlock(&s->efr_lock);
  81  }
  82
  83  static irqreturn_t sc16is7xx_irq(int irq, void *dev_id)
  84 @@ -904,6 +926,9 @@ static void sc16is7xx_set_termios(struct
  85         if (!(termios->c_cflag & CREAD))
  86                 port->ignore_status_mask |= SC16IS7XX_LSR_BRK_ERROR_MASK;
  87
  88 +       /* As above, claim the mutex while accessing the EFR. */
  89 +       mutex_lock(&s->efr_lock);
  90 +
  91         sc16is7xx_port_write(port, SC16IS7XX_LCR_REG,
  92                              SC16IS7XX_LCR_CONF_MODE_B);
  93
  94 @@ -925,6 +950,8 @@ static void sc16is7xx_set_termios(struct
  95         /* Update LCR register */
  96         sc16is7xx_port_write(port, SC16IS7XX_LCR_REG, lcr);
  97
  98 +       mutex_unlock(&s->efr_lock);
  99 +
 100         /* Get baud rate generator configuration */
 101         baud = uart_get_baud_rate(port, termios, old,
 102                                   port->uartclk / 16 / 4 / 0xffff,
 103 @@ -1187,6 +1214,7 @@ static int sc16is7xx_probe(struct device
 104         s->regmap = regmap;
 105         s->devtype = devtype;
 106         dev_set_drvdata(dev, s);
 107 +       mutex_init(&s->efr_lock);
 108
 109         kthread_init_worker(&s->kworker);
 110         kthread_init_work(&s->irq_work, sc16is7xx_ist);