1  // SPDX-License-Identifier: GPL-2.0
2  /*
3   *	6522 Versatile Interface Adapter (VIA)
4   *
5   *	There are two of these on the Mac II. Some IRQs are vectored
6   *	via them as are assorted bits and bobs - eg RTC, ADB.
7   *
8   * CSA: Motorola seems to have removed documentation on the 6522 from
9   * their web site; try
10   *     http://nerini.drf.com/vectrex/other/text/chips/6522/
11   *     http://www.zymurgy.net/classic/vic20/vicdet1.htm
12   * and
13   *     http://193.23.168.87/mikro_laborversuche/via_iobaustein/via6522_1.html
14   * for info.  A full-text web search on 6522 AND VIA will probably also
15   * net some usefulness. <cananian@alumni.princeton.edu> 20apr1999
16   *
17   * Additional data is here (the SY6522 was used in the Mac II etc):
18   *     http://www.6502.org/documents/datasheets/synertek/synertek_sy6522.pdf
19   *     http://www.6502.org/documents/datasheets/synertek/synertek_sy6522_programming_reference.pdf
20   *
21   * PRAM/RTC access algorithms are from the NetBSD RTC toolkit version 1.08b
22   * by Erik Vogan and adapted to Linux by Joshua M. Thompson (funaho@jurai.org)
23   *
24   */
25  
26  #include <linux/clocksource.h>
27  #include <linux/types.h>
28  #include <linux/kernel.h>
29  #include <linux/mm.h>
30  #include <linux/delay.h>
31  #include <linux/init.h>
32  #include <linux/module.h>
33  #include <linux/irq.h>
34  
35  #include <asm/macintosh.h>
36  #include <asm/macints.h>
37  #include <asm/mac_via.h>
38  #include <asm/mac_psc.h>
39  #include <asm/mac_oss.h>
40  
41  #include "mac.h"
42  
43  volatile __u8 *via1, *via2;
44  int rbv_present;
45  int via_alt_mapping;
46  EXPORT_SYMBOL(via_alt_mapping);
47  static __u8 rbv_clear;
48  
49  /*
50   * Globals for accessing the VIA chip registers without having to
51   * check if we're hitting a real VIA or an RBV. Normally you could
52   * just hit the combined register (ie, vIER|rIER) but that seems to
53   * break on AV Macs...probably because they actually decode more than
54   * eight address bits. Why can't Apple engineers at least be
55   * _consistently_ lazy?                          - 1999-05-21 (jmt)
56   */
57  
58  static int gIER,gIFR,gBufA,gBufB;
59  
60  /*
61   * On Macs with a genuine VIA chip there is no way to mask an individual slot
62   * interrupt. This limitation also seems to apply to VIA clone logic cores in
63   * Quadra-like ASICs. (RBV and OSS machines don't have this limitation.)
64   *
65   * We used to fake it by configuring the relevant VIA pin as an output
66   * (to mask the interrupt) or input (to unmask). That scheme did not work on
67   * (at least) the Quadra 700. A NuBus card's /NMRQ signal is an open-collector
68   * circuit (see Designing Cards and Drivers for Macintosh II and Macintosh SE,
69   * p. 10-11 etc) but VIA outputs are not (see datasheet).
70   *
71   * Driving these outputs high must cause the VIA to source current and the
72   * card to sink current when it asserts /NMRQ. Current will flow but the pin
73   * voltage is uncertain and so the /NMRQ condition may still cause a transition
74   * at the VIA2 CA1 input (which explains the lost interrupts). A side effect
75   * is that a disabled slot IRQ can never be tested as pending or not.
76   *
77   * Driving these outputs low doesn't work either. All the slot /NMRQ lines are
78   * (active low) OR'd together to generate the CA1 (aka "SLOTS") interrupt (see
79   * The Guide To Macintosh Family Hardware, 2nd edition p. 167). If we drive a
80   * disabled /NMRQ line low, the falling edge immediately triggers a CA1
81   * interrupt and all slot interrupts after that will generate no transition
82   * and therefore no interrupt, even after being re-enabled.
83   *
84   * So we make the VIA port A I/O lines inputs and use nubus_disabled to keep
85   * track of their states. When any slot IRQ becomes disabled we mask the CA1
86   * umbrella interrupt. Only when all slot IRQs become enabled do we unmask
87   * the CA1 interrupt. It must remain enabled even when cards have no interrupt
88   * handler registered. Drivers must therefore disable a slot interrupt at the
89   * device before they call free_irq (like shared and autovector interrupts).
90   *
91   * There is also a related problem when MacOS is used to boot Linux. A network
92   * card brought up by a MacOS driver may raise an interrupt while Linux boots.
93   * This can be fatal since it can't be handled until the right driver loads
94   * (if such a driver exists at all). Apparently related to this hardware
95   * limitation, "Designing Cards and Drivers", p. 9-8, says that a slot
96   * interrupt with no driver would crash MacOS (the book was written before
97   * the appearance of Macs with RBV or OSS).
98   */
99  
100  static u8 nubus_disabled;
101  
102  void via_debug_dump(void);
103  static void via_nubus_init(void);
104  
105  /*
106   * Initialize the VIAs
107   *
108   * First we figure out where they actually _are_ as well as what type of
109   * VIA we have for VIA2 (it could be a real VIA or an RBV or even an OSS.)
110   * Then we pretty much clear them out and disable all IRQ sources.
111   */
112  
via_init(void)113  void __init via_init(void)
114  {
115  	via1 = (void *)VIA1_BASE;
116  	pr_debug("VIA1 detected at %p\n", via1);
117  
118  	if (oss_present) {
119  		via2 = NULL;
120  		rbv_present = 0;
121  	} else {
122  		switch (macintosh_config->via_type) {
123  
124  		/* IIci, IIsi, IIvx, IIvi (P6xx), LC series */
125  
126  		case MAC_VIA_IICI:
127  			via2 = (void *)RBV_BASE;
128  			pr_debug("VIA2 (RBV) detected at %p\n", via2);
129  			rbv_present = 1;
130  			if (macintosh_config->ident == MAC_MODEL_LCIII) {
131  				rbv_clear = 0x00;
132  			} else {
133  				/* on most RBVs (& unlike the VIAs), you   */
134  				/* need to set bit 7 when you write to IFR */
135  				/* in order for your clear to occur.       */
136  				rbv_clear = 0x80;
137  			}
138  			gIER = rIER;
139  			gIFR = rIFR;
140  			gBufA = rSIFR;
141  			gBufB = rBufB;
142  			break;
143  
144  		/* Quadra and early MacIIs agree on the VIA locations */
145  
146  		case MAC_VIA_QUADRA:
147  		case MAC_VIA_II:
148  			via2 = (void *) VIA2_BASE;
149  			pr_debug("VIA2 detected at %p\n", via2);
150  			rbv_present = 0;
151  			rbv_clear = 0x00;
152  			gIER = vIER;
153  			gIFR = vIFR;
154  			gBufA = vBufA;
155  			gBufB = vBufB;
156  			break;
157  
158  		default:
159  			panic("UNKNOWN VIA TYPE");
160  		}
161  	}
162  
163  #ifdef DEBUG_VIA
164  	via_debug_dump();
165  #endif
166  
167  	/*
168  	 * Shut down all IRQ sources, reset the timers, and
169  	 * kill the timer latch on VIA1.
170  	 */
171  
172  	via1[vIER] = 0x7F;
173  	via1[vIFR] = 0x7F;
174  	via1[vT1CL] = 0;
175  	via1[vT1CH] = 0;
176  	via1[vT2CL] = 0;
177  	via1[vT2CH] = 0;
178  	via1[vACR] &= ~0xC0; /* setup T1 timer with no PB7 output */
179  	via1[vACR] &= ~0x03; /* disable port A & B latches */
180  
181  	/*
182  	 * SE/30: disable video IRQ
183  	 */
184  
185  	if (macintosh_config->ident == MAC_MODEL_SE30) {
186  		via1[vDirB] |= 0x40;
187  		via1[vBufB] |= 0x40;
188  	}
189  
190  	switch (macintosh_config->adb_type) {
191  	case MAC_ADB_IOP:
192  	case MAC_ADB_II:
193  	case MAC_ADB_PB1:
194  		/*
195  		 * Set the RTC bits to a known state: all lines to outputs and
196  		 * RTC disabled (yes that's 0 to enable and 1 to disable).
197  		 */
198  		via1[vDirB] |= VIA1B_vRTCEnb | VIA1B_vRTCClk | VIA1B_vRTCData;
199  		via1[vBufB] |= VIA1B_vRTCEnb | VIA1B_vRTCClk;
200  		break;
201  	}
202  
203  	/* Everything below this point is VIA2/RBV only... */
204  
205  	if (oss_present)
206  		return;
207  
208  	if ((macintosh_config->via_type == MAC_VIA_QUADRA) &&
209  	    (macintosh_config->adb_type != MAC_ADB_PB1) &&
210  	    (macintosh_config->adb_type != MAC_ADB_PB2) &&
211  	    (macintosh_config->ident    != MAC_MODEL_C660) &&
212  	    (macintosh_config->ident    != MAC_MODEL_Q840)) {
213  		via_alt_mapping = 1;
214  		via1[vDirB] |= 0x40;
215  		via1[vBufB] &= ~0x40;
216  	} else {
217  		via_alt_mapping = 0;
218  	}
219  
220  	/*
221  	 * Now initialize VIA2. For RBV we just kill all interrupts;
222  	 * for a regular VIA we also reset the timers and stuff.
223  	 */
224  
225  	via2[gIER] = 0x7F;
226  	via2[gIFR] = 0x7F | rbv_clear;
227  	if (!rbv_present) {
228  		via2[vT1CL] = 0;
229  		via2[vT1CH] = 0;
230  		via2[vT2CL] = 0;
231  		via2[vT2CH] = 0;
232  		via2[vACR] &= ~0xC0; /* setup T1 timer with no PB7 output */
233  		via2[vACR] &= ~0x03; /* disable port A & B latches */
234  	}
235  
236  	via_nubus_init();
237  
238  	/* Everything below this point is VIA2 only... */
239  
240  	if (rbv_present)
241  		return;
242  
243  	/*
244  	 * Set vPCR for control line interrupts.
245  	 *
246  	 * CA1 (SLOTS IRQ), CB1 (ASC IRQ): negative edge trigger.
247  	 *
248  	 * Macs with ESP SCSI have a negative edge triggered SCSI interrupt.
249  	 * Testing reveals that PowerBooks do too. However, the SE/30
250  	 * schematic diagram shows an active high NCR5380 IRQ line.
251  	 */
252  
253  	pr_debug("VIA2 vPCR is 0x%02X\n", via2[vPCR]);
254  	if (macintosh_config->via_type == MAC_VIA_II) {
255  		/* CA2 (SCSI DRQ), CB2 (SCSI IRQ): indep. input, pos. edge */
256  		via2[vPCR] = 0x66;
257  	} else {
258  		/* CA2 (SCSI DRQ), CB2 (SCSI IRQ): indep. input, neg. edge */
259  		via2[vPCR] = 0x22;
260  	}
261  }
262  
263  /*
264   * Debugging dump, used in various places to see what's going on.
265   */
266  
via_debug_dump(void)267  void via_debug_dump(void)
268  {
269  	printk(KERN_DEBUG "VIA1: DDRA = 0x%02X DDRB = 0x%02X ACR = 0x%02X\n",
270  		(uint) via1[vDirA], (uint) via1[vDirB], (uint) via1[vACR]);
271  	printk(KERN_DEBUG "         PCR = 0x%02X  IFR = 0x%02X IER = 0x%02X\n",
272  		(uint) via1[vPCR], (uint) via1[vIFR], (uint) via1[vIER]);
273  	if (!via2)
274  		return;
275  	if (rbv_present) {
276  		printk(KERN_DEBUG "VIA2:  IFR = 0x%02X  IER = 0x%02X\n",
277  			(uint) via2[rIFR], (uint) via2[rIER]);
278  		printk(KERN_DEBUG "      SIFR = 0x%02X SIER = 0x%02X\n",
279  			(uint) via2[rSIFR], (uint) via2[rSIER]);
280  	} else {
281  		printk(KERN_DEBUG "VIA2: DDRA = 0x%02X DDRB = 0x%02X ACR = 0x%02X\n",
282  			(uint) via2[vDirA], (uint) via2[vDirB],
283  			(uint) via2[vACR]);
284  		printk(KERN_DEBUG "         PCR = 0x%02X  IFR = 0x%02X IER = 0x%02X\n",
285  			(uint) via2[vPCR],
286  			(uint) via2[vIFR], (uint) via2[vIER]);
287  	}
288  }
289  
290  /*
291   * Flush the L2 cache on Macs that have it by flipping
292   * the system into 24-bit mode for an instant.
293   */
294  
via_l2_flush(int writeback)295  void via_l2_flush(int writeback)
296  {
297  	unsigned long flags;
298  
299  	local_irq_save(flags);
300  	via2[gBufB] &= ~VIA2B_vMode32;
301  	via2[gBufB] |= VIA2B_vMode32;
302  	local_irq_restore(flags);
303  }
304  
305  /*
306   * Initialize VIA2 for Nubus access
307   */
308  
via_nubus_init(void)309  static void __init via_nubus_init(void)
310  {
311  	/* unlock nubus transactions */
312  
313  	if ((macintosh_config->adb_type != MAC_ADB_PB1) &&
314  	    (macintosh_config->adb_type != MAC_ADB_PB2)) {
315  		/* set the line to be an output on non-RBV machines */
316  		if (!rbv_present)
317  			via2[vDirB] |= 0x02;
318  
319  		/* this seems to be an ADB bit on PMU machines */
320  		/* according to MkLinux.  -- jmt               */
321  		via2[gBufB] |= 0x02;
322  	}
323  
324  	/*
325  	 * Disable the slot interrupts. On some hardware that's not possible.
326  	 * On some hardware it's unclear what all of these I/O lines do.
327  	 */
328  
329  	switch (macintosh_config->via_type) {
330  	case MAC_VIA_II:
331  	case MAC_VIA_QUADRA:
332  		pr_debug("VIA2 vDirA is 0x%02X\n", via2[vDirA]);
333  		break;
334  	case MAC_VIA_IICI:
335  		/* RBV. Disable all the slot interrupts. SIER works like IER. */
336  		via2[rSIER] = 0x7F;
337  		break;
338  	}
339  }
340  
via_nubus_irq_startup(int irq)341  void via_nubus_irq_startup(int irq)
342  {
343  	int irq_idx = IRQ_IDX(irq);
344  
345  	switch (macintosh_config->via_type) {
346  	case MAC_VIA_II:
347  	case MAC_VIA_QUADRA:
348  		/* Make the port A line an input. Probably redundant. */
349  		if (macintosh_config->via_type == MAC_VIA_II) {
350  			/* The top two bits are RAM size outputs. */
351  			via2[vDirA] &= 0xC0 | ~(1 << irq_idx);
352  		} else {
353  			/* Allow NuBus slots 9 through F. */
354  			via2[vDirA] &= 0x80 | ~(1 << irq_idx);
355  		}
356  		fallthrough;
357  	case MAC_VIA_IICI:
358  		via_irq_enable(irq);
359  		break;
360  	}
361  }
362  
via_nubus_irq_shutdown(int irq)363  void via_nubus_irq_shutdown(int irq)
364  {
365  	switch (macintosh_config->via_type) {
366  	case MAC_VIA_II:
367  	case MAC_VIA_QUADRA:
368  		/* Ensure that the umbrella CA1 interrupt remains enabled. */
369  		via_irq_enable(irq);
370  		break;
371  	case MAC_VIA_IICI:
372  		via_irq_disable(irq);
373  		break;
374  	}
375  }
376  
377  /*
378   * The generic VIA interrupt routines (shamelessly stolen from Alan Cox's
379   * via6522.c :-), disable/pending masks added.
380   */
381  
382  #define VIA_TIMER_1_INT BIT(6)
383  
via1_irq(struct irq_desc * desc)384  void via1_irq(struct irq_desc *desc)
385  {
386  	int irq_num;
387  	unsigned char irq_bit, events;
388  
389  	events = via1[vIFR] & via1[vIER] & 0x7F;
390  	if (!events)
391  		return;
392  
393  	irq_num = IRQ_MAC_TIMER_1;
394  	irq_bit = VIA_TIMER_1_INT;
395  	if (events & irq_bit) {
396  		unsigned long flags;
397  
398  		local_irq_save(flags);
399  		via1[vIFR] = irq_bit;
400  		generic_handle_irq(irq_num);
401  		local_irq_restore(flags);
402  
403  		events &= ~irq_bit;
404  		if (!events)
405  			return;
406  	}
407  
408  	irq_num = VIA1_SOURCE_BASE;
409  	irq_bit = 1;
410  	do {
411  		if (events & irq_bit) {
412  			via1[vIFR] = irq_bit;
413  			generic_handle_irq(irq_num);
414  		}
415  		++irq_num;
416  		irq_bit <<= 1;
417  	} while (events >= irq_bit);
418  }
419  
via2_irq(struct irq_desc * desc)420  static void via2_irq(struct irq_desc *desc)
421  {
422  	int irq_num;
423  	unsigned char irq_bit, events;
424  
425  	events = via2[gIFR] & via2[gIER] & 0x7F;
426  	if (!events)
427  		return;
428  
429  	irq_num = VIA2_SOURCE_BASE;
430  	irq_bit = 1;
431  	do {
432  		if (events & irq_bit) {
433  			via2[gIFR] = irq_bit | rbv_clear;
434  			generic_handle_irq(irq_num);
435  		}
436  		++irq_num;
437  		irq_bit <<= 1;
438  	} while (events >= irq_bit);
439  }
440  
441  /*
442   * Dispatch Nubus interrupts. We are called as a secondary dispatch by the
443   * VIA2 dispatcher as a fast interrupt handler.
444   */
445  
via_nubus_irq(struct irq_desc * desc)446  static void via_nubus_irq(struct irq_desc *desc)
447  {
448  	int slot_irq;
449  	unsigned char slot_bit, events;
450  
451  	events = ~via2[gBufA] & 0x7F;
452  	if (rbv_present)
453  		events &= via2[rSIER];
454  	else
455  		events &= ~via2[vDirA];
456  	if (!events)
457  		return;
458  
459  	do {
460  		slot_irq = IRQ_NUBUS_F;
461  		slot_bit = 0x40;
462  		do {
463  			if (events & slot_bit) {
464  				events &= ~slot_bit;
465  				generic_handle_irq(slot_irq);
466  			}
467  			--slot_irq;
468  			slot_bit >>= 1;
469  		} while (events);
470  
471   		/* clear the CA1 interrupt and make certain there's no more. */
472  		via2[gIFR] = 0x02 | rbv_clear;
473  		events = ~via2[gBufA] & 0x7F;
474  		if (rbv_present)
475  			events &= via2[rSIER];
476  		else
477  			events &= ~via2[vDirA];
478  	} while (events);
479  }
480  
481  /*
482   * Register the interrupt dispatchers for VIA or RBV machines only.
483   */
484  
via_register_interrupts(void)485  void __init via_register_interrupts(void)
486  {
487  	if (via_alt_mapping) {
488  		/* software interrupt */
489  		irq_set_chained_handler(IRQ_AUTO_1, via1_irq);
490  		/* via1 interrupt */
491  		irq_set_chained_handler(IRQ_AUTO_6, via1_irq);
492  	} else {
493  		irq_set_chained_handler(IRQ_AUTO_1, via1_irq);
494  	}
495  	irq_set_chained_handler(IRQ_AUTO_2, via2_irq);
496  	irq_set_chained_handler(IRQ_MAC_NUBUS, via_nubus_irq);
497  }
498  
via_irq_enable(int irq)499  void via_irq_enable(int irq) {
500  	int irq_src	= IRQ_SRC(irq);
501  	int irq_idx	= IRQ_IDX(irq);
502  
503  	if (irq_src == 1) {
504  		via1[vIER] = IER_SET_BIT(irq_idx);
505  	} else if (irq_src == 2) {
506  		if (irq != IRQ_MAC_NUBUS || nubus_disabled == 0)
507  			via2[gIER] = IER_SET_BIT(irq_idx);
508  	} else if (irq_src == 7) {
509  		switch (macintosh_config->via_type) {
510  		case MAC_VIA_II:
511  		case MAC_VIA_QUADRA:
512  			nubus_disabled &= ~(1 << irq_idx);
513  			/* Enable the CA1 interrupt when no slot is disabled. */
514  			if (!nubus_disabled)
515  				via2[gIER] = IER_SET_BIT(1);
516  			break;
517  		case MAC_VIA_IICI:
518  			/* On RBV, enable the slot interrupt.
519  			 * SIER works like IER.
520  			 */
521  			via2[rSIER] = IER_SET_BIT(irq_idx);
522  			break;
523  		}
524  	}
525  }
526  
via_irq_disable(int irq)527  void via_irq_disable(int irq) {
528  	int irq_src	= IRQ_SRC(irq);
529  	int irq_idx	= IRQ_IDX(irq);
530  
531  	if (irq_src == 1) {
532  		via1[vIER] = IER_CLR_BIT(irq_idx);
533  	} else if (irq_src == 2) {
534  		via2[gIER] = IER_CLR_BIT(irq_idx);
535  	} else if (irq_src == 7) {
536  		switch (macintosh_config->via_type) {
537  		case MAC_VIA_II:
538  		case MAC_VIA_QUADRA:
539  			nubus_disabled |= 1 << irq_idx;
540  			if (nubus_disabled)
541  				via2[gIER] = IER_CLR_BIT(1);
542  			break;
543  		case MAC_VIA_IICI:
544  			via2[rSIER] = IER_CLR_BIT(irq_idx);
545  			break;
546  		}
547  	}
548  }
549  
via1_set_head(int head)550  void via1_set_head(int head)
551  {
552  	if (head == 0)
553  		via1[vBufA] &= ~VIA1A_vHeadSel;
554  	else
555  		via1[vBufA] |= VIA1A_vHeadSel;
556  }
557  EXPORT_SYMBOL(via1_set_head);
558  
via2_scsi_drq_pending(void)559  int via2_scsi_drq_pending(void)
560  {
561  	return via2[gIFR] & (1 << IRQ_IDX(IRQ_MAC_SCSIDRQ));
562  }
563  EXPORT_SYMBOL(via2_scsi_drq_pending);
564  
565  /* timer and clock source */
566  
567  #define VIA_CLOCK_FREQ     783360                /* VIA "phase 2" clock in Hz */
568  #define VIA_TIMER_CYCLES   (VIA_CLOCK_FREQ / HZ) /* clock cycles per jiffy */
569  
570  #define VIA_TC             (VIA_TIMER_CYCLES - 2) /* including 0 and -1 */
571  #define VIA_TC_LOW         (VIA_TC & 0xFF)
572  #define VIA_TC_HIGH        (VIA_TC >> 8)
573  
574  static u64 mac_read_clk(struct clocksource *cs);
575  
576  static struct clocksource mac_clk = {
577  	.name   = "via1",
578  	.rating = 250,
579  	.read   = mac_read_clk,
580  	.mask   = CLOCKSOURCE_MASK(32),
581  	.flags  = CLOCK_SOURCE_IS_CONTINUOUS,
582  };
583  
584  static u32 clk_total, clk_offset;
585  
via_timer_handler(int irq,void * dev_id)586  static irqreturn_t via_timer_handler(int irq, void *dev_id)
587  {
588  	clk_total += VIA_TIMER_CYCLES;
589  	clk_offset = 0;
590  	legacy_timer_tick(1);
591  
592  	return IRQ_HANDLED;
593  }
594  
via_init_clock(void)595  void __init via_init_clock(void)
596  {
597  	if (request_irq(IRQ_MAC_TIMER_1, via_timer_handler, IRQF_TIMER, "timer",
598  			NULL)) {
599  		pr_err("Couldn't register %s interrupt\n", "timer");
600  		return;
601  	}
602  
603  	via1[vT1CL] = VIA_TC_LOW;
604  	via1[vT1CH] = VIA_TC_HIGH;
605  	via1[vACR] |= 0x40;
606  
607  	clocksource_register_hz(&mac_clk, VIA_CLOCK_FREQ);
608  }
609  
mac_read_clk(struct clocksource * cs)610  static u64 mac_read_clk(struct clocksource *cs)
611  {
612  	unsigned long flags;
613  	u8 count_high;
614  	u16 count;
615  	u32 ticks;
616  
617  	/*
618  	 * Timer counter wrap-around is detected with the timer interrupt flag
619  	 * but reading the counter low byte (vT1CL) would reset the flag.
620  	 * Also, accessing both counter registers is essentially a data race.
621  	 * These problems are avoided by ignoring the low byte. Clock accuracy
622  	 * is 256 times worse (error can reach 0.327 ms) but CPU overhead is
623  	 * reduced by avoiding slow VIA register accesses.
624  	 */
625  
626  	local_irq_save(flags);
627  	count_high = via1[vT1CH];
628  	if (count_high == 0xFF)
629  		count_high = 0;
630  	if (count_high > 0 && (via1[vIFR] & VIA_TIMER_1_INT))
631  		clk_offset = VIA_TIMER_CYCLES;
632  	count = count_high << 8;
633  	ticks = VIA_TIMER_CYCLES - count;
634  	ticks += clk_offset + clk_total;
635  	local_irq_restore(flags);
636  
637  	return ticks;
638  }
639