target/linux/brcm2708/patches-4.19/950-0034-amba_pl011-Round-input-clock-up.patch

   1 From 610cb34f3d7c5fdffb0db82538731714a2df1d13 Mon Sep 17 00:00:00 2001
   2 From: Phil Elwell <phil@raspberrypi.org>
   3 Date: Wed, 1 Mar 2017 16:07:39 +0000
   4 Subject: [PATCH] amba_pl011: Round input clock up
   5
   6 The UART clock is initialised to be as close to the requested
   7 frequency as possible without exceeding it. Now that there is a
   8 clock manager that returns the actual frequencies, an expected
   9 48MHz clock is reported as 47999625. If the requested baudrate
  10 == requested clock/16, there is no headroom and the slight
  11 reduction in actual clock rate results in failure.
  12
  13 Detect cases where it looks like a "round" clock was chosen and
  14 adjust the reported clock to match that "round" value. As the
  15 code comment says:
  16
  17 /*
  18  * If increasing a clock by less than 0.1% changes it
  19  * from ..999.. to ..000.., round up.
  20  */
  21
  22 Signed-off-by: Phil Elwell <phil@raspberrypi.org>
  23 ---
  24  drivers/tty/serial/amba-pl011.c | 23 +++++++++++++++++++++--
  25  1 file changed, 21 insertions(+), 2 deletions(-)
  26
  27 --- a/drivers/tty/serial/amba-pl011.c
  28 +++ b/drivers/tty/serial/amba-pl011.c
  29 @@ -1650,6 +1650,23 @@ static void pl011_put_poll_char(struct u
  30
  31  #endif /* CONFIG_CONSOLE_POLL */
  32
  33 +unsigned long pl011_clk_round(unsigned long clk)
  34 +{
  35 +       unsigned long scaler;
  36 +
  37 +       /*
  38 +        * If increasing a clock by less than 0.1% changes it
  39 +        * from ..999.. to ..000.., round up.
  40 +        */
  41 +       scaler = 1;
  42 +       while (scaler * 100000 < clk)
  43 +               scaler *= 10;
  44 +       if ((clk + scaler - 1)/scaler % 1000 == 0)
  45 +               clk = (clk/scaler + 1) * scaler;
  46 +
  47 +       return clk;
  48 +}
  49 +
  50  static int pl011_hwinit(struct uart_port *port)
  51  {
  52         struct uart_amba_port *uap =
  53 @@ -1666,7 +1683,7 @@ static int pl011_hwinit(struct uart_port
  54         if (retval)
  55                 return retval;
  56
  57 -       uap->port.uartclk = clk_get_rate(uap->clk);
  58 +       uap->port.uartclk = pl011_clk_round(clk_get_rate(uap->clk));
  59
  60         /* Clear pending error and receive interrupts */
  61         pl011_write(UART011_OEIS | UART011_BEIS | UART011_PEIS |
  62 @@ -2322,7 +2339,7 @@ static int __init pl011_console_setup(st
  63                         plat->init();
  64         }
  65
  66 -       uap->port.uartclk = clk_get_rate(uap->clk);
  67 +       uap->port.uartclk = pl011_clk_round(clk_get_rate(uap->clk));
  68
  69         if (uap->vendor->fixed_options) {
  70                 baud = uap->fixed_baud;
  71 @@ -2507,6 +2524,7 @@ static struct uart_driver amba_reg = {
  72         .cons                   = AMBA_CONSOLE,
  73  };
  74
  75 +#if 0
  76  static int pl011_probe_dt_alias(int index, struct device *dev)
  77  {
  78         struct device_node *np;
  79 @@ -2538,6 +2556,7 @@ static int pl011_probe_dt_alias(int inde
  80
  81         return ret;
  82  }
  83 +#endif
  84
  85  /* unregisters the driver also if no more ports are left */
  86  static void pl011_unregister_port(struct uart_amba_port *uap)