arch/arm/mach-rpc/time.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *  linux/arch/arm/common/time-acorn.c
   4  *
   5  *  Copyright (c) 1996-2000 Russell King.
   6  *
   7  *  Changelog:
   8  *   24-Sep-1996        RMK     Created
   9  *   10-Oct-1996        RMK     Brought up to date with arch-sa110eval
  10  *   04-Dec-1997        RMK     Updated for new arch/arm/time.c
  11  *   13=Jun-2004        DS      Moved to arch/arm/common b/c shared w/CLPS7500
  12  */
  13 #include <linux/clocksource.h>
  14 #include <linux/init.h>
  15 #include <linux/interrupt.h>
  16 #include <linux/irq.h>
  17 #include <linux/io.h>
  18
  19 #include <mach/hardware.h>
  20 #include <asm/hardware/ioc.h>
  21
  22 #include <asm/mach/time.h>
  23
  24 #define RPC_CLOCK_FREQ 2000000
  25 #define RPC_LATCH DIV_ROUND_CLOSEST(RPC_CLOCK_FREQ, HZ)
  26
  27 static u32 ioc_time;
  28
  29 static u64 ioc_timer_read(struct clocksource *cs)
  30 {
  31         unsigned int count1, count2, status;
  32         unsigned long flags;
  33         u32 ticks;
  34
  35         local_irq_save(flags);
  36         ioc_writeb (0, IOC_T0LATCH);
  37         barrier ();
  38         count1 = ioc_readb(IOC_T0CNTL) | (ioc_readb(IOC_T0CNTH) << 8);
  39         barrier ();
  40         status = ioc_readb(IOC_IRQREQA);
  41         barrier ();
  42         ioc_writeb (0, IOC_T0LATCH);
  43         barrier ();
  44         count2 = ioc_readb(IOC_T0CNTL) | (ioc_readb(IOC_T0CNTH) << 8);
  45         ticks = ioc_time + RPC_LATCH - count2;
  46         local_irq_restore(flags);
  47
  48         if (count2 < count1) {
  49                 /*
  50                  * The timer has not reloaded between reading count1 and
  51                  * count2, check whether an interrupt was actually pending.
  52                  */
  53                 if (status & (1 << 5))
  54                         ticks += RPC_LATCH;
  55         } else if (count2 > count1) {
  56                 /*
  57                  * The timer has reloaded, so count2 indicates the new
  58                  * count since the wrap.  The interrupt would not have
  59                  * been processed, so add the missed ticks.
  60                  */
  61                 ticks += RPC_LATCH;
  62         }
  63
  64         return ticks;
  65 }
  66
  67 static struct clocksource ioctime_clocksource = {
  68         .read = ioc_timer_read,
  69         .mask = CLOCKSOURCE_MASK(32),
  70         .rating = 100,
  71 };
  72
  73 void __init ioctime_init(void)
  74 {
  75         ioc_writeb(RPC_LATCH & 255, IOC_T0LTCHL);
  76         ioc_writeb(RPC_LATCH >> 8, IOC_T0LTCHH);
  77         ioc_writeb(0, IOC_T0GO);
  78 }
  79
  80 static irqreturn_t
  81 ioc_timer_interrupt(int irq, void *dev_id)
  82 {
  83         ioc_time += RPC_LATCH;
  84         timer_tick();
  85         return IRQ_HANDLED;
  86 }
  87
  88 /*
  89  * Set up timer interrupt.
  90  */
  91 void __init ioc_timer_init(void)
  92 {
  93         WARN_ON(clocksource_register_hz(&ioctime_clocksource, RPC_CLOCK_FREQ));
  94         ioctime_init();
  95         if (request_irq(IRQ_TIMER0, ioc_timer_interrupt, 0, "timer", NULL))
  96                 pr_err("Failed to request irq %d (timer)\n", IRQ_TIMER0);
  97 }