Hello Jan,
On 09/06/2023 23:04:12+0200, Jan Kiszka wrote:
> From: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
>
> The VL bit in the seconds register remains set only until seconds are
> written under main power. As this often happens during boot-up after
> picking up a network time, make sure to preserve the low battery state
> across this, caching it and returning it via the RTC_VL_BACKUP_LOW bit.
>
> To permit userspace clearing this state during runtime, also implement
> RTC_VL_CLR that works against the cached state.
>
> This is emulating RTCs which have a battery voltage check that works
> under main power as well.
>
Emulating doesn't work well and I deliberately chose to not implement
it. For example, in your scenario, if you boot twice without using
VL_READ, you anyway have lost the information. This makes emulating
unreliabl. The fix you need is in userspace where you have to ensure you
read the status before setting the time.
> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
> ---
> drivers/rtc/rtc-pcf8563.c | 17 ++++++++++++++---
> 1 file changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/rtc/rtc-pcf8563.c b/drivers/rtc/rtc-pcf8563.c
> index 7e720472213c..f8c6cdb9a39d 100644
> --- a/drivers/rtc/rtc-pcf8563.c
> +++ b/drivers/rtc/rtc-pcf8563.c
> @@ -81,6 +81,7 @@ struct pcf8563 {
> #ifdef CONFIG_COMMON_CLK
> struct clk_hw clkout_hw;
> #endif
> + bool low_bat;
> };
>
> static int pcf8563_read_block_data(struct i2c_client *client, unsigned char reg,
> @@ -207,6 +208,7 @@ static int pcf8563_rtc_read_time(struct device *dev, struct rtc_time *tm)
> return err;
>
> if (buf[PCF8563_REG_SC] & PCF8563_SC_LV) {
> + pcf8563->low_bat = true;
> dev_err(&client->dev,
> "low voltage detected, date/time is not reliable.\n");
> return -EINVAL;
> @@ -277,6 +279,8 @@ static int pcf8563_rtc_set_time(struct device *dev, struct rtc_time *tm)
> static int pcf8563_rtc_ioctl(struct device *dev, unsigned int cmd, unsigned long arg)
> {
> struct i2c_client *client = to_i2c_client(dev);
> + struct pcf8563 *pcf8563 = i2c_get_clientdata(client);
> + unsigned int state = 0;
> int ret;
>
> switch (cmd) {
> @@ -284,9 +288,16 @@ static int pcf8563_rtc_ioctl(struct device *dev, unsigned int cmd, unsigned long
> ret = i2c_smbus_read_byte_data(client, PCF8563_REG_SC);
> if (ret < 0)
> return ret;
> -
> - return put_user(ret & PCF8563_SC_LV ? RTC_VL_DATA_INVALID : 0,
> - (unsigned int __user *)arg);
> + if (ret & PCF8563_SC_LV) {
> + state |= RTC_VL_DATA_INVALID;
> + pcf8563->low_bat = true;
> + }
> + if (pcf8563->low_bat)
> + state |= RTC_VL_BACKUP_LOW;
> + return put_user(state, (unsigned int __user *)arg);
> + case RTC_VL_CLR:
> + pcf8563->low_bat = false;
> + return 0;
> default:
> return -ENOIOCTLCMD;
> }
> --
> 2.35.3
--
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
