cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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rtc-dm355evm.c (3629B)

      1// SPDX-License-Identifier: GPL-2.0+
      2/*
      3 * rtc-dm355evm.c - access battery-backed counter in MSP430 firmware
      4 *
      5 * Copyright (c) 2008 by David Brownell
      6 */
      7#include <linux/kernel.h>
      8#include <linux/init.h>
      9#include <linux/rtc.h>
     10#include <linux/platform_device.h>
     11
     12#include <linux/mfd/dm355evm_msp.h>
     13#include <linux/module.h>
     14
     15
     16/*
     17 * The MSP430 firmware on the DM355 EVM uses a watch crystal to feed
     18 * a 1 Hz counter.  When a backup battery is supplied, that makes a
     19 * reasonable RTC for applications where alarms and non-NTP drift
     20 * compensation aren't important.
     21 *
     22 * The only real glitch is the inability to read or write all four
     23 * counter bytes atomically:  the count may increment in the middle
     24 * of an operation, causing trouble when the LSB rolls over.
     25 *
     26 * This driver was tested with firmware revision A4.
     27 */
     28union evm_time {
     29	u8	bytes[4];
     30	u32	value;
     31};
     32
     33static int dm355evm_rtc_read_time(struct device *dev, struct rtc_time *tm)
     34{
     35	union evm_time	time;
     36	int		status;
     37	int		tries = 0;
     38
     39	do {
     40		/*
     41		 * Read LSB(0) to MSB(3) bytes.  Defend against the counter
     42		 * rolling over by re-reading until the value is stable,
     43		 * and assuming the four reads take at most a few seconds.
     44		 */
     45		status = dm355evm_msp_read(DM355EVM_MSP_RTC_0);
     46		if (status < 0)
     47			return status;
     48		if (tries && time.bytes[0] == status)
     49			break;
     50		time.bytes[0] = status;
     51
     52		status = dm355evm_msp_read(DM355EVM_MSP_RTC_1);
     53		if (status < 0)
     54			return status;
     55		if (tries && time.bytes[1] == status)
     56			break;
     57		time.bytes[1] = status;
     58
     59		status = dm355evm_msp_read(DM355EVM_MSP_RTC_2);
     60		if (status < 0)
     61			return status;
     62		if (tries && time.bytes[2] == status)
     63			break;
     64		time.bytes[2] = status;
     65
     66		status = dm355evm_msp_read(DM355EVM_MSP_RTC_3);
     67		if (status < 0)
     68			return status;
     69		if (tries && time.bytes[3] == status)
     70			break;
     71		time.bytes[3] = status;
     72
     73	} while (++tries < 5);
     74
     75	dev_dbg(dev, "read timestamp %08x\n", time.value);
     76
     77	rtc_time64_to_tm(le32_to_cpu(time.value), tm);
     78	return 0;
     79}
     80
     81static int dm355evm_rtc_set_time(struct device *dev, struct rtc_time *tm)
     82{
     83	union evm_time	time;
     84	unsigned long	value;
     85	int		status;
     86
     87	value = rtc_tm_to_time64(tm);
     88	time.value = cpu_to_le32(value);
     89
     90	dev_dbg(dev, "write timestamp %08x\n", time.value);
     91
     92	/*
     93	 * REVISIT handle non-atomic writes ... maybe just retry until
     94	 * byte[1] sticks (no rollover)?
     95	 */
     96	status = dm355evm_msp_write(time.bytes[0], DM355EVM_MSP_RTC_0);
     97	if (status < 0)
     98		return status;
     99
    100	status = dm355evm_msp_write(time.bytes[1], DM355EVM_MSP_RTC_1);
    101	if (status < 0)
    102		return status;
    103
    104	status = dm355evm_msp_write(time.bytes[2], DM355EVM_MSP_RTC_2);
    105	if (status < 0)
    106		return status;
    107
    108	status = dm355evm_msp_write(time.bytes[3], DM355EVM_MSP_RTC_3);
    109	if (status < 0)
    110		return status;
    111
    112	return 0;
    113}
    114
    115static const struct rtc_class_ops dm355evm_rtc_ops = {
    116	.read_time	= dm355evm_rtc_read_time,
    117	.set_time	= dm355evm_rtc_set_time,
    118};
    119
    120/*----------------------------------------------------------------------*/
    121
    122static int dm355evm_rtc_probe(struct platform_device *pdev)
    123{
    124	struct rtc_device *rtc;
    125
    126	rtc = devm_rtc_allocate_device(&pdev->dev);
    127	if (IS_ERR(rtc))
    128		return PTR_ERR(rtc);
    129
    130	platform_set_drvdata(pdev, rtc);
    131
    132	rtc->ops = &dm355evm_rtc_ops;
    133	rtc->range_max = U32_MAX;
    134
    135	return devm_rtc_register_device(rtc);
    136}
    137
    138/*
    139 * I2C is used to talk to the MSP430, but this platform device is
    140 * exposed by an MFD driver that manages I2C communications.
    141 */
    142static struct platform_driver rtc_dm355evm_driver = {
    143	.probe		= dm355evm_rtc_probe,
    144	.driver		= {
    145		.name	= "rtc-dm355evm",
    146	},
    147};
    148
    149module_platform_driver(rtc_dm355evm_driver);
    150
    151MODULE_LICENSE("GPL");