On Tue, Oct 6, 2020 at 1:20 PM Tomasz Figa <tfiga@xxxxxxxxxxxx> wrote:
>
> Hi Sakari,
>
> On Thu, Sep 3, 2020 at 10:15 AM Sakari Ailus
> <sakari.ailus@xxxxxxxxxxxxxxx> wrote:
> >
> > In certain use cases (where the chip is part of a camera module, and the
> > camera module is wired together with a camera privacy LED), powering on
> > the device during probe is undesirable. Add support for the at24 to
> > execute probe while being powered off. For this to happen, a hint in form
> > of a device property is required from the firmware.
> >
> > Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> > ---
> > drivers/misc/eeprom/at24.c | 43 +++++++++++++++++++++++---------------
> > 1 file changed, 26 insertions(+), 17 deletions(-)
> >
> > diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
> > index 8f5de5f10bbea..2d24e33788d7d 100644
> > --- a/drivers/misc/eeprom/at24.c
> > +++ b/drivers/misc/eeprom/at24.c
> > @@ -595,6 +595,7 @@ static int at24_probe(struct i2c_client *client)
> > bool i2c_fn_i2c, i2c_fn_block;
> > unsigned int i, num_addresses;
> > struct at24_data *at24;
> > + bool low_power;
> > struct regmap *regmap;
> > bool writable;
> > u8 test_byte;
> > @@ -733,25 +734,30 @@ static int at24_probe(struct i2c_client *client)
> >
> > i2c_set_clientdata(client, at24);
> >
> > - err = regulator_enable(at24->vcc_reg);
> > - if (err) {
> > - dev_err(dev, "Failed to enable vcc regulator\n");
> > - return err;
> > - }
> > + low_power = acpi_dev_state_low_power(&client->dev);
> > + if (!low_power) {
> > + err = regulator_enable(at24->vcc_reg);
> > + if (err) {
> > + dev_err(dev, "Failed to enable vcc regulator\n");
> > + return err;
> > + }
> >
> > - /* enable runtime pm */
> > - pm_runtime_set_active(dev);
> > + pm_runtime_set_active(dev);
> > + }
> > pm_runtime_enable(dev);
> >
>
> What's the guarantee that at this point the runtime PM wouldn't
> suspend the device? Notice that the nvmem device is already exposed to
> the userspace, which could trigger pm runtime gets and puts (and thus
> idles as well).
>
> Best regards,
> Tomasz
>
> > /*
> > - * Perform a one-byte test read to verify that the
> > - * chip is functional.
> > + * Perform a one-byte test read to verify that the chip is functional,
> > + * unless powering on the device is to be avoided during probe (i.e.
> > + * it's powered off right now).
> > */
> > - err = at24_read(at24, 0, &test_byte, 1);
Actually never mind. Someone pointed out to me that at24_read() calls
pm_runtime_get_sync() internally, so we should be fine. Sorry, for the
noise.
Best regards,
Tomasz
> > - if (err) {
> > - pm_runtime_disable(dev);
> > - regulator_disable(at24->vcc_reg);
> > - return -ENODEV;
> > + if (!low_power) {
> > + err = at24_read(at24, 0, &test_byte, 1);
> > + if (err) {
> > + pm_runtime_disable(dev);
> > + regulator_disable(at24->vcc_reg);
> > + return -ENODEV;
> > + }
> > }
> >
> > pm_runtime_idle(dev);
> > @@ -771,9 +777,11 @@ static int at24_remove(struct i2c_client *client)
> > struct at24_data *at24 = i2c_get_clientdata(client);
> >
> > pm_runtime_disable(&client->dev);
> > - if (!pm_runtime_status_suspended(&client->dev))
> > - regulator_disable(at24->vcc_reg);
> > - pm_runtime_set_suspended(&client->dev);
> > + if (!acpi_dev_state_low_power(&client->dev)) {
> > + if (!pm_runtime_status_suspended(&client->dev))
> > + regulator_disable(at24->vcc_reg);
> > + pm_runtime_set_suspended(&client->dev);
> > + }
> >
> > return 0;
> > }
> > @@ -810,6 +818,7 @@ static struct i2c_driver at24_driver = {
> > .probe_new = at24_probe,
> > .remove = at24_remove,
> > .id_table = at24_ids,
> > + .flags = I2C_DRV_FL_ALLOW_LOW_POWER_PROBE,
> > };
> >
> > static int __init at24_init(void)
> > --
> > 2.20.1
> >
