On 05/05/2023 10:31:38+0000, Johannes Kirchmair wrote:
> Hello Alex,
>
> > -----Original Message-----
> > From: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>
> > Sent: Donnerstag, 4. Mai 2023 11:13
> > To: Johannes Kirchmair <johannes.kirchmair@xxxxxxxxxxx>
> > Cc: linux-rtc@xxxxxxxxxxxxxxx
> > Subject: Re: [PATCH] disable clkout for rv3028 by default
> >
> > CAUTION: External E-Mail !
> >
> > On 04/05/2023 10:32:17+0200, Johannes Kirchmair wrote:
> > > The rv3028 chip is kind of strange.
> > > The chip has two inputs one for the buffer battery
> > > (V_backup) and one for the main power supply (V_dd).
> > > By default a clk out of the chip is enabled, drawing a big amount of
> > > current, draining the buffer battery of our board in 3 days.
> > > There is a mode that would shut down the clk out if powered from
> > > V_backup, but that would have to be configured as well. In our
> > > application the battery is connected via V_dd. So disabling the clk by
> > > default is the way to go for us.
> > >
> >
> > You can't do that, this introduces a glitch in the clock output and will
> > break existing users. The clock should be disabled automatically by the
> > CCF when there are no users. Is your kernel built without
> > CONFIG_COMMON_CLK
> Now I am a little confused.
> I tested on an x86 board where the clock was not disabled by the kernel.
> Than I tested on an arm imx8 board where it was disabled by default.
>
> In both cases I used an 5.15 kernel.
>
> Difference between x86 and arm is, that in x86 we probe from user space after boot process and on the arm board the rtc is probed while booting.
>
> Do you know at what point the clock is disabled? Is it part of registering the clock?
>
This is clk_disable_unused which is a late_initcall_sync()
> Best regards Johannes
>
> >
> > > Signed-off-by: Johannes Kirchmair <johannes.kirchmair@xxxxxxxxxxx>
> > > ---
> > > drivers/rtc/rtc-rv3028.c | 12 +++++++++++-
> > > 1 file changed, 11 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/rtc/rtc-rv3028.c b/drivers/rtc/rtc-rv3028.c
> > > index 12c807306893..9e2aaa7a533e 100644
> > > --- a/drivers/rtc/rtc-rv3028.c
> > > +++ b/drivers/rtc/rtc-rv3028.c
> > > @@ -787,7 +787,7 @@ static const struct regmap_config regmap_config = {
> > > static int rv3028_probe(struct i2c_client *client)
> > > {
> > > struct rv3028_data *rv3028;
> > > - int ret, status;
> > > + int ret, status, buf;
> > > u32 ohms;
> > > struct nvmem_config nvmem_cfg = {
> > > .name = "rv3028_nvram",
> > > @@ -826,6 +826,16 @@ static int rv3028_probe(struct i2c_client *client)
> > > if (status & RV3028_STATUS_AF)
> > > dev_warn(&client->dev, "An alarm may have been missed.\n");
> > >
> > > + ret = regmap_read(rv3028->regmap, RV3028_CLKOUT, &buf);
> > > + if (ret < 0)
> > > + return ret;
> > > +
> > > + if (buf != RV3028_CLKOUT_FD_MASK) {
> > > + ret = rv3028_update_cfg(rv3028, RV3028_CLKOUT, 0xff,
> > RV3028_CLKOUT_FD_MASK); // disable clk out
> > > + if (ret < 0)
> > > + return ret;
> > > + }
> > > +
> > > rv3028->rtc = devm_rtc_allocate_device(&client->dev);
> > > if (IS_ERR(rv3028->rtc))
> > > return PTR_ERR(rv3028->rtc);
> > > --
> > > 2.25.1
> > >
> >
> > --
> > Alexandre Belloni, co-owner and COO, Bootlin
> > Embedded Linux and Kernel engineering
> > https://bootlin.com
--
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
