git.ipfire.org Git - thirdparty/openembedded/openembedded-core-contrib.git/blob

   1
   2 From: Petr Vandrovec <vandrove@vc.cvut.cz>
   3
   4 Patch below adds support for using different prescaler than 16 for 16c950
   5 chips.  This is needed for using Fujitsu-Siemens Connect2Air compact-flash
   6 card, which comes (apparently) with 806kHz clocks, and so you have to
   7 program prescaler for division by 7, and DLAB to 1, to get 115200Bd.
   8
   9 To get card properly running you also have to add lines below to
  10 /etc/pcmcia/serial.opts so kernel knows that base speed is not 115200 but
  11 50400 (50400 * 16 = 806400; 806400 / 7 = 115200).  As I've found no code
  12 specifying baud_rate in serial_cs, I assume that specifying it in
  13 serial.opts is right way to do this type of things.
  14
  15 Patch also fixes problem that for UPF_MAGIC_MULTIPLIER maximum possible
  16 baud rate passed to uart code was uartclk / 16 while correct value for
  17 these devices (and for 16c950) is uartclk / 4.
  18
  19 Patch also fixes problem that for UPF_MAGIC_MULTIPLIER devices with
  20 baud_rate 19200 or 9600 spd_cust did not work correctly.  Not that such
  21 devices exist, but we should not ignore spd_cust, user probably knows why
  22 he asked for spd_cust.
  23
  24 serial.opts:
  25
  26 case "$MANFID-$FUNCID-$PRODID_1-$PRODID_2-$PRODID_3-$PRODID_4" in
  27 '0279,950b-2-GPRS Modem---')
  28     SERIAL_OPTS="baud_base 50400"
  29     ;;
  30 esac
  31
  32 Cc: David Woodhouse <dwmw2@infradead.org>
  33 Signed-off-by: Andrew Morton <akpm@osdl.org>
  34 ---
  35
  36  drivers/serial/8250.c |   82 +++++++++++++++++++++++++++++++++++++++-----------
  37  1 file changed, 64 insertions(+), 18 deletions(-)
  38
  39 Index: linux-2.6.21/drivers/serial/8250.c
  40 ===================================================================
  41 --- linux-2.6.21.orig/drivers/serial/8250.c     2007-07-01 16:59:52.000000000 +0100
  42 +++ linux-2.6.21/drivers/serial/8250.c  2007-07-01 17:01:21.000000000 +0100
  43 @@ -1964,24 +1964,58 @@ static void serial8250_shutdown(struct u
  44                 serial_unlink_irq_chain(up);
  45  }
  46
  47 -static unsigned int serial8250_get_divisor(struct uart_port *port, unsigned int baud)
  48 +static unsigned int serial8250_get_divisor(struct uart_port *port, unsigned int baud,
  49 +                                          unsigned int *prescaler)
  50  {
  51 -       unsigned int quot;
  52 -
  53 -       /*
  54 -        * Handle magic divisors for baud rates above baud_base on
  55 -        * SMSC SuperIO chips.
  56 +        /*
  57 +        * Use special handling only if user did not supply its own divider.
  58 +        * spd_cust is defined in terms of baud_base, so always use default
  59 +        * prescaler when spd_cust is requested.
  60          */
  61 -       if ((port->flags & UPF_MAGIC_MULTIPLIER) &&
  62 -           baud == (port->uartclk/4))
  63 -               quot = 0x8001;
  64 -       else if ((port->flags & UPF_MAGIC_MULTIPLIER) &&
  65 -                baud == (port->uartclk/8))
  66 -               quot = 0x8002;
  67 -       else
  68 -               quot = uart_get_divisor(port, baud);
  69
  70 -       return quot;
  71 +       *prescaler = 16;
  72 +        if (baud != 38400 || (port->flags & UPF_SPD_MASK) != UPF_SPD_CUST) {
  73 +               unsigned int quot = port->uartclk / baud;
  74 +
  75 +               /*
  76 +                * Handle magic divisors for baud rates above baud_base on
  77 +                * SMSC SuperIO chips.
  78 +                */
  79 +               if (port->flags & UPF_MAGIC_MULTIPLIER) {
  80 +                       if (quot == 4) {
  81 +                               return 0x8001;
  82 +                       } else if (quot == 8) {
  83 +                               return 0x8002;
  84 +                       }
  85 +               }
  86 +               if (port->type == PORT_16C950) {
  87 +                       /*
  88 +                        * This computes TCR value (4 to 16), not CPR value (which can
  89 +                        * be between 1.000 and 31.875) - chip I have uses XTAL of
  90 +                        * 806400Hz, and so a division by 7 is required to get 115200Bd.
  91 +                        * I'm leaving CPR disabled for now, until someone will
  92 +                        * hit even more exotic XTAL (it is needed to get 500kbps
  93 +                        * or 1000kbps from 18.432MHz XTAL, but I have no device
  94 +                        * which would benefit from doing that).
  95 +                        *
  96 +                        * If we can use divide by 16, use it.  Otherwise look for
  97 +                        * better prescaler, from 15 to 4.  If quotient cannot
  98 +                        * be divided by any integer value between 4 and 15, use 4.
  99 +                        */
 100 +                       if (quot & 0x0F) {
 101 +                               unsigned int div;
 102 +
 103 +                               for (div = 15; div > 4; div--) {
 104 +                                       if (quot % div == 0) {
 105 +                                               break;
 106 +                                       }
 107 +                               }
 108 +                               *prescaler = div;
 109 +                               return quot / div;
 110 +                       }
 111 +               }
 112 +       }
 113 +       return uart_get_divisor(port, baud);
 114  }
 115
 116  static void
 117 @@ -1991,7 +2025,7 @@ serial8250_set_termios(struct uart_port
 118         struct uart_8250_port *up = (struct uart_8250_port *)port;
 119         unsigned char cval, fcr = 0;
 120         unsigned long flags;
 121 -       unsigned int baud, quot;
 122 +       unsigned int baud, quot, prescaler;
 123
 124         switch (termios->c_cflag & CSIZE) {
 125         case CS5:
 126 @@ -2023,8 +2057,13 @@ serial8250_set_termios(struct uart_port
 127         /*
 128          * Ask the core to calculate the divisor for us.
 129          */
 130 -       baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk/16);
 131 -       quot = serial8250_get_divisor(port, baud);
 132 +       if (port->type == PORT_16C950 || (port->flags & UPF_MAGIC_MULTIPLIER)) {
 133 +               baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk/4);
 134 +       } else {
 135 +               baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk/16);
 136 +       }
 137 +       quot = serial8250_get_divisor(port, baud, &prescaler);
 138 +
 139
 140         /*
 141          * Oxford Semi 952 rev B workaround
 142 @@ -2139,6 +2178,13 @@ serial8250_set_termios(struct uart_port
 143         serial_dl_write(up, quot);
 144
 145         /*
 146 +        * Program prescaler for 16C950 chips.
 147 +        */
 148 +       if (up->port.type == PORT_16C950) {
 149 +               serial_icr_write(up, UART_TCR, prescaler == 16 ? 0 : prescaler);
 150 +       }
 151 +
 152 +       /*
 153          * LCR DLAB must be set to enable 64-byte FIFO mode. If the FCR
 154          * is written without DLAB set, this mode will be disabled.
 155          */