From e3edd67141a1ea5294e54b17fee5becf1090f5d4 Mon Sep 17 00:00:00 2001 From: Nishanth Menon Date: Mon, 20 Apr 2015 19:51:34 -0500 Subject: [PATCH] rtc: ds1307: Enable the mcp794xx alarm after programming time Alarm interrupt enable register is at offset 0x7, while the time registers for the alarm follow that. When we program Alarm interrupt enable prior to programming the time, it is possible that previous time value could be close or match at the time of alarm enable resulting in interrupt trigger which is unexpected (and does not match the time we expect it to trigger). To prevent this scenario from occuring, program the ALM0_EN bit only after the alarm time is appropriately programmed. Ofcourse, I2C programming is non-atomic, so there are loopholes where the interrupt wont trigger if the time requested is in the past at the time of programming the ALM0_EN bit. However, we will not have unexpected interrupts while the time is programmed after the interrupt are enabled. Signed-off-by: Nishanth Menon Reviewed-by: Grygorii Strashko Signed-off-by: Alexandre Belloni --- drivers/rtc/rtc-ds1307.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c index 4ffabb322a9a..6e76de1856fc 100644 --- a/drivers/rtc/rtc-ds1307.c +++ b/drivers/rtc/rtc-ds1307.c @@ -742,17 +742,17 @@ static int mcp794xx_set_alarm(struct device *dev, struct rtc_wkalrm *t) regs[6] &= ~MCP794XX_BIT_ALMX_IF; /* Set alarm match: second, minute, hour, day, date, month. */ regs[6] |= MCP794XX_MSK_ALMX_MATCH; - - if (t->enabled) - regs[0] |= MCP794XX_BIT_ALM0_EN; - else - regs[0] &= ~MCP794XX_BIT_ALM0_EN; + /* Disable interrupt. We will not enable until completely programmed */ + regs[0] &= ~MCP794XX_BIT_ALM0_EN; ret = ds1307->write_block_data(client, MCP794XX_REG_CONTROL, 10, regs); if (ret < 0) return ret; - return 0; + if (!t->enabled) + return 0; + regs[0] |= MCP794XX_BIT_ALM0_EN; + return i2c_smbus_write_byte_data(client, MCP794XX_REG_CONTROL, regs[0]); } static int mcp794xx_alarm_irq_enable(struct device *dev, unsigned int enabled) -- 2.39.2