staging: comedi: dt282x: refactor dt282x_ns_to_timer()

Define the pacer clock limits and remove the magic numbers. Refactor
the code to use a common path to return the actual 'ns' timing and
the timer divisor value.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/comedi/drivers/dt282x.c b/drivers/staging/comedi/drivers/dt282x.c
index 06a87a1..e6958ea 100644 (file)
--- a/drivers/staging/comedi/drivers/dt282x.c
+++ b/drivers/staging/comedi/drivers/dt282x.c
@@ -113,6 +113,17 @@
 #define DT2821_SUPCSR_XCLK             BIT(1)
 #define DT2821_SUPCSR_BDINIT           BIT(0)
 #define DT2821_TMRCTR_REG              0x0e
+#define DT2821_TMRCTR_PRESCALE(x)      (((x) & 0xf) << 8)
+#define DT2821_TMRCTR_DIVIDER(x)       ((255 - ((x) & 0xff)) << 0)
+
+/* Pacer Clock */
+#define DT2821_OSC_BASE                250     /* 4 MHz (in nanoseconds) */
+#define DT2821_PRESCALE(x)     BIT(x)
+#define DT2821_PRESCALE_MAX    15
+#define DT2821_DIVIDER_MAX     255
+#define DT2821_OSC_MAX         (DT2821_OSC_BASE *                      \
+                                DT2821_PRESCALE(DT2821_PRESCALE_MAX) * \
+                                DT2821_DIVIDER_MAX)
 
 static const struct comedi_lrange range_dt282x_ai_lo_bipolar = {
        4, {
@@ -365,10 +376,10 @@ static unsigned int dt282x_ns_to_timer(unsigned int *ns, unsigned int flags)
 {
        unsigned int prescale, base, divider;
 
-       for (prescale = 0; prescale < 16; prescale++) {
-               if (prescale == 1)
+       for (prescale = 0; prescale <= DT2821_PRESCALE_MAX; prescale++) {
+               if (prescale == 1)      /* 0 and 1 are both divide by 1 */
                        continue;
-               base = 250 * (1 << prescale);
+               base = DT2821_OSC_BASE * DT2821_PRESCALE(prescale);
                switch (flags & CMDF_ROUND_MASK) {
                case CMDF_ROUND_NEAREST:
                default:
@@ -381,15 +392,17 @@ static unsigned int dt282x_ns_to_timer(unsigned int *ns, unsigned int flags)
                        divider = DIV_ROUND_UP(*ns, base);
                        break;
                }
-               if (divider < 256) {
-                       *ns = divider * base;
-                       return (prescale << 8) | (255 - divider);
-               }
+               if (divider <= DT2821_DIVIDER_MAX)
+                       break;
+       }
+       if (divider > DT2821_DIVIDER_MAX) {
+               prescale = DT2821_PRESCALE_MAX;
+               divider = DT2821_DIVIDER_MAX;
+               base = DT2821_OSC_BASE * DT2821_PRESCALE(prescale);
        }
-       base = 250 * (1 << 15);
-       divider = 255;
        *ns = divider * base;
-       return (15 << 8) | (255 - divider);
+       return DT2821_TMRCTR_PRESCALE(prescale) |
+              DT2821_TMRCTR_DIVIDER(divider);
 }
 
 static void dt282x_munge(struct comedi_device *dev,
@@ -689,8 +702,7 @@ static int dt282x_ai_cmdtest(struct comedi_device *dev,
 
        err |= comedi_check_trigger_arg_min(&cmd->convert_arg, 4000);
 
-#define SLOWEST_TIMER  (250*(1<<15)*255)
-       err |= comedi_check_trigger_arg_max(&cmd->convert_arg, SLOWEST_TIMER);
+       err |= comedi_check_trigger_arg_max(&cmd->convert_arg, DT2821_OSC_MAX);
        err |= comedi_check_trigger_arg_min(&cmd->convert_arg, board->ai_speed);
        err |= comedi_check_trigger_arg_is(&cmd->scan_end_arg,
                                           cmd->chanlist_len);