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linux/drivers/rtc/rtc-mcp795.c
Gustavo A. R. Silva fed9b18611 rtc: remove VLA usage 
In preparation to enabling -Wvla, remove VLA and replace it
with a fixed-length array instead.

>From a security viewpoint, the use of Variable Length Arrays can be
a vector for stack overflow attacks. Also, in general, as the code
evolves it is easy to lose track of how big a VLA can get. Thus, we
can end up having segfaults that are hard to debug.

Also, fixed as part of the directive to remove all VLAs from
the kernel: https://lkml.org/lkml/2018/3/7/621

Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
2018-03-17 14:20:56 +01:00

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/*
* SPI Driver for Microchip MCP795 RTC
*
* Copyright (C) Josef Gajdusek <atx@atx.name>
*
* based on other Linux RTC drivers
*
* Device datasheet:
* http://ww1.microchip.com/downloads/en/DeviceDoc/22280A.pdf
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
*/
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/device.h>
#include <linux/printk.h>
#include <linux/spi/spi.h>
#include <linux/rtc.h>
#include <linux/of.h>
#include <linux/bcd.h>
#include <linux/delay.h>
/* MCP795 Instructions, see datasheet table 3-1 */
#define MCP795_EEREAD 0x03
#define MCP795_EEWRITE 0x02
#define MCP795_EEWRDI 0x04
#define MCP795_EEWREN 0x06
#define MCP795_SRREAD 0x05
#define MCP795_SRWRITE 0x01
#define MCP795_READ 0x13
#define MCP795_WRITE 0x12
#define MCP795_UNLOCK 0x14
#define MCP795_IDWRITE 0x32
#define MCP795_IDREAD 0x33
#define MCP795_CLRWDT 0x44
#define MCP795_CLRRAM 0x54
/* MCP795 RTCC registers, see datasheet table 4-1 */
#define MCP795_REG_SECONDS 0x01
#define MCP795_REG_DAY 0x04
#define MCP795_REG_MONTH 0x06
#define MCP795_REG_CONTROL 0x08
#define MCP795_REG_ALM0_SECONDS 0x0C
#define MCP795_REG_ALM0_DAY 0x0F
#define MCP795_ST_BIT BIT(7)
#define MCP795_24_BIT BIT(6)
#define MCP795_LP_BIT BIT(5)
#define MCP795_EXTOSC_BIT BIT(3)
#define MCP795_OSCON_BIT BIT(5)
#define MCP795_ALM0_BIT BIT(4)
#define MCP795_ALM1_BIT BIT(5)
#define MCP795_ALM0IF_BIT BIT(3)
#define MCP795_ALM0C0_BIT BIT(4)
#define MCP795_ALM0C1_BIT BIT(5)
#define MCP795_ALM0C2_BIT BIT(6)
#define SEC_PER_DAY (24 * 60 * 60)
static int mcp795_rtcc_read(struct device *dev, u8 addr, u8 *buf, u8 count)
{
struct spi_device *spi = to_spi_device(dev);
int ret;
u8 tx[2];
tx[0] = MCP795_READ;
tx[1] = addr;
ret = spi_write_then_read(spi, tx, sizeof(tx), buf, count);
if (ret)
dev_err(dev, "Failed reading %d bytes from address %x.\n",
count, addr);
return ret;
}
static int mcp795_rtcc_write(struct device *dev, u8 addr, u8 *data, u8 count)
{
struct spi_device *spi = to_spi_device(dev);
int ret;
u8 tx[257];
tx[0] = MCP795_WRITE;
tx[1] = addr;
memcpy(&tx[2], data, count);
ret = spi_write(spi, tx, 2 + count);
if (ret)
dev_err(dev, "Failed to write %d bytes to address %x.\n",
count, addr);
return ret;
}
static int mcp795_rtcc_set_bits(struct device *dev, u8 addr, u8 mask, u8 state)
{
int ret;
u8 tmp;
ret = mcp795_rtcc_read(dev, addr, &tmp, 1);
if (ret)
return ret;
if ((tmp & mask) != state) {
tmp = (tmp & ~mask) | state;
ret = mcp795_rtcc_write(dev, addr, &tmp, 1);
}
return ret;
}
static int mcp795_stop_oscillator(struct device *dev, bool *extosc)
{
int retries = 5;
int ret;
u8 data;
ret = mcp795_rtcc_set_bits(dev, MCP795_REG_SECONDS, MCP795_ST_BIT, 0);
if (ret)
return ret;
ret = mcp795_rtcc_read(dev, MCP795_REG_CONTROL, &data, 1);
if (ret)
return ret;
*extosc = !!(data & MCP795_EXTOSC_BIT);
ret = mcp795_rtcc_set_bits(
dev, MCP795_REG_CONTROL, MCP795_EXTOSC_BIT, 0);
if (ret)
return ret;
/* wait for the OSCON bit to clear */
do {
usleep_range(700, 800);
ret = mcp795_rtcc_read(dev, MCP795_REG_DAY, &data, 1);
if (ret)
break;
if (!(data & MCP795_OSCON_BIT))
break;
} while (--retries);
return !retries ? -EIO : ret;
}
static int mcp795_start_oscillator(struct device *dev, bool *extosc)
{
if (extosc) {
u8 data = *extosc ? MCP795_EXTOSC_BIT : 0;
int ret;
ret = mcp795_rtcc_set_bits(
dev, MCP795_REG_CONTROL, MCP795_EXTOSC_BIT, data);
if (ret)
return ret;
}
return mcp795_rtcc_set_bits(
dev, MCP795_REG_SECONDS, MCP795_ST_BIT, MCP795_ST_BIT);
}
/* Enable or disable Alarm 0 in RTC */
static int mcp795_update_alarm(struct device *dev, bool enable)
{
int ret;
dev_dbg(dev, "%s alarm\n", enable ? "Enable" : "Disable");
if (enable) {
/* clear ALM0IF (Alarm 0 Interrupt Flag) bit */
ret = mcp795_rtcc_set_bits(dev, MCP795_REG_ALM0_DAY,
MCP795_ALM0IF_BIT, 0);
if (ret)
return ret;
/* enable alarm 0 */
ret = mcp795_rtcc_set_bits(dev, MCP795_REG_CONTROL,
MCP795_ALM0_BIT, MCP795_ALM0_BIT);
} else {
/* disable alarm 0 and alarm 1 */
ret = mcp795_rtcc_set_bits(dev, MCP795_REG_CONTROL,
MCP795_ALM0_BIT | MCP795_ALM1_BIT, 0);
}
return ret;
}
static int mcp795_set_time(struct device *dev, struct rtc_time *tim)
{
int ret;
u8 data[7];
bool extosc;
/* Stop RTC and store current value of EXTOSC bit */
ret = mcp795_stop_oscillator(dev, &extosc);
if (ret)
return ret;
/* Read first, so we can leave config bits untouched */
ret = mcp795_rtcc_read(dev, MCP795_REG_SECONDS, data, sizeof(data));
if (ret)
return ret;
data[0] = (data[0] & 0x80) | bin2bcd(tim->tm_sec);
data[1] = (data[1] & 0x80) | bin2bcd(tim->tm_min);
data[2] = bin2bcd(tim->tm_hour);
data[3] = (data[3] & 0xF8) | bin2bcd(tim->tm_wday + 1);
data[4] = bin2bcd(tim->tm_mday);
data[5] = (data[5] & MCP795_LP_BIT) | bin2bcd(tim->tm_mon + 1);
if (tim->tm_year > 100)
tim->tm_year -= 100;
data[6] = bin2bcd(tim->tm_year);
/* Always write the date and month using a separate Write command.
* This is a workaround for a know silicon issue that some combinations
* of date and month values may result in the date being reset to 1.
*/
ret = mcp795_rtcc_write(dev, MCP795_REG_SECONDS, data, 5);
if (ret)
return ret;
ret = mcp795_rtcc_write(dev, MCP795_REG_MONTH, &data[5], 2);
if (ret)
return ret;
/* Start back RTC and restore previous value of EXTOSC bit.
* There is no need to clear EXTOSC bit when the previous value was 0
* because it was already cleared when stopping the RTC oscillator.
*/
ret = mcp795_start_oscillator(dev, extosc ? &extosc : NULL);
if (ret)
return ret;
dev_dbg(dev, "Set mcp795: %04d-%02d-%02d(%d) %02d:%02d:%02d\n",
tim->tm_year + 1900, tim->tm_mon, tim->tm_mday,
tim->tm_wday, tim->tm_hour, tim->tm_min, tim->tm_sec);
return 0;
}
static int mcp795_read_time(struct device *dev, struct rtc_time *tim)
{
int ret;
u8 data[7];
ret = mcp795_rtcc_read(dev, MCP795_REG_SECONDS, data, sizeof(data));
if (ret)
return ret;
tim->tm_sec = bcd2bin(data[0] & 0x7F);
tim->tm_min = bcd2bin(data[1] & 0x7F);
tim->tm_hour = bcd2bin(data[2] & 0x3F);
tim->tm_wday = bcd2bin(data[3] & 0x07) - 1;
tim->tm_mday = bcd2bin(data[4] & 0x3F);
tim->tm_mon = bcd2bin(data[5] & 0x1F) - 1;
tim->tm_year = bcd2bin(data[6]) + 100; /* Assume we are in 20xx */
dev_dbg(dev, "Read from mcp795: %04d-%02d-%02d(%d) %02d:%02d:%02d\n",
tim->tm_year + 1900, tim->tm_mon, tim->tm_mday,
tim->tm_wday, tim->tm_hour, tim->tm_min, tim->tm_sec);
return 0;
}
static int mcp795_set_alarm(struct device *dev, struct rtc_wkalrm *alm)
{
struct rtc_time now_tm;
time64_t now;
time64_t later;
u8 tmp[6];
int ret;
/* Read current time from RTC hardware */
ret = mcp795_read_time(dev, &now_tm);
if (ret)
return ret;
/* Get the number of seconds since 1970 */
now = rtc_tm_to_time64(&now_tm);
later = rtc_tm_to_time64(&alm->time);
if (later <= now)
return -EINVAL;
/* make sure alarm fires within the next one year */
if ((later - now) >=
(SEC_PER_DAY * (365 + is_leap_year(alm->time.tm_year))))
return -EDOM;
/* disable alarm */
ret = mcp795_update_alarm(dev, false);
if (ret)
return ret;
/* Read registers, so we can leave configuration bits untouched */
ret = mcp795_rtcc_read(dev, MCP795_REG_ALM0_SECONDS, tmp, sizeof(tmp));
if (ret)
return ret;
alm->time.tm_year = -1;
alm->time.tm_isdst = -1;
alm->time.tm_yday = -1;
tmp[0] = (tmp[0] & 0x80) | bin2bcd(alm->time.tm_sec);
tmp[1] = (tmp[1] & 0x80) | bin2bcd(alm->time.tm_min);
tmp[2] = (tmp[2] & 0xE0) | bin2bcd(alm->time.tm_hour);
tmp[3] = (tmp[3] & 0x80) | bin2bcd(alm->time.tm_wday + 1);
/* set alarm match: seconds, minutes, hour, day, date and month */
tmp[3] |= (MCP795_ALM0C2_BIT | MCP795_ALM0C1_BIT | MCP795_ALM0C0_BIT);
tmp[4] = (tmp[4] & 0xC0) | bin2bcd(alm->time.tm_mday);
tmp[5] = (tmp[5] & 0xE0) | bin2bcd(alm->time.tm_mon + 1);
ret = mcp795_rtcc_write(dev, MCP795_REG_ALM0_SECONDS, tmp, sizeof(tmp));
if (ret)
return ret;
/* enable alarm if requested */
if (alm->enabled) {
ret = mcp795_update_alarm(dev, true);
if (ret)
return ret;
dev_dbg(dev, "Alarm IRQ armed\n");
}
dev_dbg(dev, "Set alarm: %02d-%02d(%d) %02d:%02d:%02d\n",
alm->time.tm_mon, alm->time.tm_mday, alm->time.tm_wday,
alm->time.tm_hour, alm->time.tm_min, alm->time.tm_sec);
return 0;
}
static int mcp795_read_alarm(struct device *dev, struct rtc_wkalrm *alm)
{
u8 data[6];
int ret;
ret = mcp795_rtcc_read(
dev, MCP795_REG_ALM0_SECONDS, data, sizeof(data));
if (ret)
return ret;
alm->time.tm_sec = bcd2bin(data[0] & 0x7F);
alm->time.tm_min = bcd2bin(data[1] & 0x7F);
alm->time.tm_hour = bcd2bin(data[2] & 0x1F);
alm->time.tm_wday = bcd2bin(data[3] & 0x07) - 1;
alm->time.tm_mday = bcd2bin(data[4] & 0x3F);
alm->time.tm_mon = bcd2bin(data[5] & 0x1F) - 1;
alm->time.tm_year = -1;
alm->time.tm_isdst = -1;
alm->time.tm_yday = -1;
dev_dbg(dev, "Read alarm: %02d-%02d(%d) %02d:%02d:%02d\n",
alm->time.tm_mon, alm->time.tm_mday, alm->time.tm_wday,
alm->time.tm_hour, alm->time.tm_min, alm->time.tm_sec);
return 0;
}
static int mcp795_alarm_irq_enable(struct device *dev, unsigned int enabled)
{
return mcp795_update_alarm(dev, !!enabled);
}
static irqreturn_t mcp795_irq(int irq, void *data)
{
struct spi_device *spi = data;
struct rtc_device *rtc = spi_get_drvdata(spi);
struct mutex *lock = &rtc->ops_lock;
int ret;
mutex_lock(lock);
/* Disable alarm.
* There is no need to clear ALM0IF (Alarm 0 Interrupt Flag) bit,
* because it is done every time when alarm is enabled.
*/
ret = mcp795_update_alarm(&spi->dev, false);
if (ret)
dev_err(&spi->dev,
"Failed to disable alarm in IRQ (ret=%d)\n", ret);
rtc_update_irq(rtc, 1, RTC_AF | RTC_IRQF);
mutex_unlock(lock);
return IRQ_HANDLED;
}
static const struct rtc_class_ops mcp795_rtc_ops = {
.read_time = mcp795_read_time,
.set_time = mcp795_set_time,
.read_alarm = mcp795_read_alarm,
.set_alarm = mcp795_set_alarm,
.alarm_irq_enable = mcp795_alarm_irq_enable
};
static int mcp795_probe(struct spi_device *spi)
{
struct rtc_device *rtc;
int ret;
spi->mode = SPI_MODE_0;
spi->bits_per_word = 8;
ret = spi_setup(spi);
if (ret) {
dev_err(&spi->dev, "Unable to setup SPI\n");
return ret;
}
/* Start the oscillator but don't set the value of EXTOSC bit */
mcp795_start_oscillator(&spi->dev, NULL);
/* Clear the 12 hour mode flag*/
mcp795_rtcc_set_bits(&spi->dev, 0x03, MCP795_24_BIT, 0);
rtc = devm_rtc_device_register(&spi->dev, "rtc-mcp795",
&mcp795_rtc_ops, THIS_MODULE);
if (IS_ERR(rtc))
return PTR_ERR(rtc);
spi_set_drvdata(spi, rtc);
if (spi->irq > 0) {
dev_dbg(&spi->dev, "Alarm support enabled\n");
/* Clear any pending alarm (ALM0IF bit) before requesting
* the interrupt.
*/
mcp795_rtcc_set_bits(&spi->dev, MCP795_REG_ALM0_DAY,
MCP795_ALM0IF_BIT, 0);
ret = devm_request_threaded_irq(&spi->dev, spi->irq, NULL,
mcp795_irq, IRQF_TRIGGER_FALLING | IRQF_ONESHOT,
dev_name(&rtc->dev), spi);
if (ret)
dev_err(&spi->dev, "Failed to request IRQ: %d: %d\n",
spi->irq, ret);
else
device_init_wakeup(&spi->dev, true);
}
return 0;
}
#ifdef CONFIG_OF
static const struct of_device_id mcp795_of_match[] = {
{ .compatible = "maxim,mcp795" },
{ }
};
MODULE_DEVICE_TABLE(of, mcp795_of_match);
#endif
static struct spi_driver mcp795_driver = {
.driver = {
.name = "rtc-mcp795",
.of_match_table = of_match_ptr(mcp795_of_match),
},
.probe = mcp795_probe,
};
module_spi_driver(mcp795_driver);
MODULE_DESCRIPTION("MCP795 RTC SPI Driver");
MODULE_AUTHOR("Josef Gajdusek <atx@atx.name>");
MODULE_LICENSE("GPL");
MODULE_ALIAS("spi:mcp795");
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