1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* 3 * Support code for virtual Ranchu board for MIPS. 4 * 5 * Author: Miodrag Dinic <miodrag.dinic@mips.com> 6 */ 7 8 #include <linux/of_address.h> 9 #include <linux/types.h> 10 11 #include <asm/machine.h> 12 #include <asm/mipsregs.h> 13 #include <asm/time.h> 14 15 #define GOLDFISH_TIMER_LOW 0x00 16 #define GOLDFISH_TIMER_HIGH 0x04 17 18 static __init u64 read_rtc_time(void __iomem *base) 19 { 20 u32 time_low; 21 u32 time_high; 22 23 /* 24 * Reading the low address latches the high value 25 * as well so there is no fear that we may read 26 * inaccurate high value. 27 */ 28 time_low = readl(base + GOLDFISH_TIMER_LOW); 29 time_high = readl(base + GOLDFISH_TIMER_HIGH); 30 31 return ((u64)time_high << 32) | time_low; 32 } 33 34 static __init unsigned int ranchu_measure_hpt_freq(void) 35 { 36 u64 rtc_start, rtc_current, rtc_delta; 37 unsigned int start, count; 38 struct device_node *np; 39 void __iomem *rtc_base; 40 41 np = of_find_compatible_node(NULL, NULL, "google,goldfish-rtc"); 42 if (!np) 43 panic("%s(): Failed to find 'google,goldfish-rtc' dt node!", 44 __func__); 45 46 rtc_base = of_iomap(np, 0); 47 if (!rtc_base) 48 panic("%s(): Failed to ioremap Goldfish RTC base!", __func__); 49 50 /* 51 * Poll the nanosecond resolution RTC for one 52 * second to calibrate the CPU frequency. 53 */ 54 rtc_start = read_rtc_time(rtc_base); 55 start = read_c0_count(); 56 57 do { 58 rtc_current = read_rtc_time(rtc_base); 59 rtc_delta = rtc_current - rtc_start; 60 } while (rtc_delta < NSEC_PER_SEC); 61 62 count = read_c0_count() - start; 63 64 /* 65 * Make sure the frequency will be a round number. 66 * Without this correction, the returned value may vary 67 * between subsequent emulation executions. 68 * 69 * TODO: Set this value using device tree. 70 */ 71 count += 5000; 72 count -= count % 10000; 73 74 iounmap(rtc_base); 75 76 return count; 77 } 78 79 static const struct of_device_id ranchu_of_match[] __initconst = { 80 { 81 .compatible = "mti,ranchu", 82 }, 83 {} 84 }; 85 86 MIPS_MACHINE(ranchu) = { 87 .matches = ranchu_of_match, 88 .measure_hpt_freq = ranchu_measure_hpt_freq, 89 }; 90