drivers/rtc/rtc-macsmc.c

// SPDX-License-Identifier: GPL-2.0-only OR MIT
/*
 * Apple SMC RTC driver
 * Copyright The Asahi Linux Contributors
 */

#include <linux/bitops.h>
#include <linux/mfd/macsmc.h>
#include <linux/module.h>
#include <linux/nvmem-consumer.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/rtc.h>
#include <linux/slab.h>

/* 48-bit RTC */
#define RTC_BYTES 6
#define RTC_BITS (8 * RTC_BYTES)

/* 32768 Hz clock */
#define RTC_SEC_SHIFT 15

struct macsmc_rtc {
	struct device *dev;
	struct apple_smc *smc;
	struct rtc_device *rtc_dev;
	struct nvmem_cell *rtc_offset;
};

static int macsmc_rtc_get_time(struct device *dev, struct rtc_time *tm)
{
	struct macsmc_rtc *rtc = dev_get_drvdata(dev);
	u64 ctr = 0, off = 0;
	time64_t now;
	void *p_off;
	size_t len;
	int ret;

	ret = apple_smc_read(rtc->smc, SMC_KEY(CLKM), &ctr, RTC_BYTES);
	if (ret < 0)
		return ret;
	if (ret != RTC_BYTES)
		return -EIO;

	p_off = nvmem_cell_read(rtc->rtc_offset, &len);
	if (IS_ERR(p_off))
		return PTR_ERR(p_off);
	if (len < RTC_BYTES) {
		kfree(p_off);
		return -EIO;
	}

	memcpy(&off, p_off, RTC_BYTES);
	kfree(p_off);

	/* Sign extend from 48 to 64 bits, then arithmetic shift right 15 bits to get seconds */
	now = sign_extend64(ctr + off, RTC_BITS - 1) >> RTC_SEC_SHIFT;
	rtc_time64_to_tm(now, tm);

	return ret;
}

static int macsmc_rtc_set_time(struct device *dev, struct rtc_time *tm)
{
	struct macsmc_rtc *rtc = dev_get_drvdata(dev);
	u64 ctr = 0, off = 0;
	int ret;

	ret = apple_smc_read(rtc->smc, SMC_KEY(CLKM), &ctr, RTC_BYTES);
	if (ret < 0)
		return ret;
	if (ret != RTC_BYTES)
		return -EIO;

	/* This sets the offset such that the set second begins now */
	off = (rtc_tm_to_time64(tm) << RTC_SEC_SHIFT) - ctr;
	return nvmem_cell_write(rtc->rtc_offset, &off, RTC_BYTES);
}

static const struct rtc_class_ops macsmc_rtc_ops = {
	.read_time = macsmc_rtc_get_time,
	.set_time = macsmc_rtc_set_time,
};

static int macsmc_rtc_probe(struct platform_device *pdev)
{
	struct apple_smc *smc = dev_get_drvdata(pdev->dev.parent);
	struct macsmc_rtc *rtc;

	/*
	 * MFD will probe this device even without a node in the device tree,
	 * thus bail out early if the SMC on the current machines does not
	 * support RTC and has no node in the device tree.
	 */
	if (!pdev->dev.of_node)
		return -ENODEV;

	rtc = devm_kzalloc(&pdev->dev, sizeof(*rtc), GFP_KERNEL);
	if (!rtc)
		return -ENOMEM;

	rtc->dev = &pdev->dev;
	rtc->smc = smc;

	rtc->rtc_offset = devm_nvmem_cell_get(&pdev->dev, "rtc_offset");
	if (IS_ERR(rtc->rtc_offset))
		return dev_err_probe(&pdev->dev, PTR_ERR(rtc->rtc_offset),
				     "Failed to get rtc_offset NVMEM cell\n");

	rtc->rtc_dev = devm_rtc_allocate_device(&pdev->dev);
	if (IS_ERR(rtc->rtc_dev))
		return PTR_ERR(rtc->rtc_dev);

	rtc->rtc_dev->ops = &macsmc_rtc_ops;
	rtc->rtc_dev->range_min = S64_MIN >> (RTC_SEC_SHIFT + (64 - RTC_BITS));
	rtc->rtc_dev->range_max = S64_MAX >> (RTC_SEC_SHIFT + (64 - RTC_BITS));

	platform_set_drvdata(pdev, rtc);

	return devm_rtc_register_device(rtc->rtc_dev);
}

static const struct of_device_id macsmc_rtc_of_table[] = {
	{ .compatible = "apple,smc-rtc", },
	{}
};
MODULE_DEVICE_TABLE(of, macsmc_rtc_of_table);

static struct platform_driver macsmc_rtc_driver = {
	.driver = {
		.name = "macsmc-rtc",
		.of_match_table = macsmc_rtc_of_table,
	},
	.probe = macsmc_rtc_probe,
};
module_platform_driver(macsmc_rtc_driver);

MODULE_LICENSE("Dual MIT/GPL");
MODULE_DESCRIPTION("Apple SMC RTC driver");
MODULE_AUTHOR("Hector Martin <marcan@marcan.st>");