Re: [PATCH] iio: light: cm32181: Fix PM support on system with 2 I2C resources

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 1/17/23 17:09, Kai-Heng Feng wrote:
> Commit c1e62062ff54 ("iio: light: cm32181: Handle CM3218 ACPI devices
> with 2 I2C resources") creates a second client for the actual I2C
> address, but the "struct device" passed to PM ops is the first client
> that can't talk to the sensor.
> 
> That means the I2C transfers in both suspend and resume routines can
> fail and blocking the whole suspend process.
> 
> Instead of using the first client for I2C transfer, store the cm32181
> private struct on both cases so the PM ops can get the correct I2C
> client to perfrom suspend and resume.
> 
> Fixes: 68c1b3dd5c48 ("iio: light: cm32181: Add PM support")
> Tested-by: Wahaj <wahajaved@protonmail.com>
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>

Thank you for this fix. I had looking into this on my todo list,
since I have been seeing some bug reports about this too.

One remark inline:

> ---
>  drivers/iio/light/cm32181.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iio/light/cm32181.c b/drivers/iio/light/cm32181.c
> index 001055d097509..0f319c891353c 100644
> --- a/drivers/iio/light/cm32181.c
> +++ b/drivers/iio/light/cm32181.c
> @@ -440,6 +440,8 @@ static int cm32181_probe(struct i2c_client *client)
>  	if (!indio_dev)
>  		return -ENOMEM;
>  
> +	i2c_set_clientdata(client, indio_dev);
> +

Why move this up, the suspend/resume callbacks cannot run until
probe() completes, so no need for this change.

>  	/*
>  	 * Some ACPI systems list 2 I2C resources for the CM3218 sensor, the
>  	 * SMBus Alert Response Address (ARA, 0x0c) and the actual I2C address.
> @@ -458,9 +460,9 @@ static int cm32181_probe(struct i2c_client *client)
>  		client = i2c_acpi_new_device(dev, 1, &board_info);
>  		if (IS_ERR(client))
>  			return PTR_ERR(client);
> -	}
>  
> -	i2c_set_clientdata(client, indio_dev);
> +		i2c_set_clientdata(client, indio_dev);
> +	}

And moving it inside the if block here (instead of just dropping it)
is also weird. I guess you meant to just delete it since you moved it up.

>  
>  	cm32181 = iio_priv(indio_dev);
>  	cm32181->client = client;

Also note that the ->client used in suspend/resume now is not set until
here, so moving the i2c_set_clientdata() up really does not do anything.

I beleive it would be best to just these 2 hunks from the patch and
only keep the changes to the suspend/resume callbacks.

Regards,

Hans


> @@ -490,7 +492,8 @@ static int cm32181_probe(struct i2c_client *client)
>  
>  static int cm32181_suspend(struct device *dev)
>  {
> -	struct i2c_client *client = to_i2c_client(dev);
> +	struct cm32181_chip *cm32181 = iio_priv(dev_get_drvdata(dev));
> +	struct i2c_client *client = cm32181->client;
>  
>  	return i2c_smbus_write_word_data(client, CM32181_REG_ADDR_CMD,
>  					 CM32181_CMD_ALS_DISABLE);
> @@ -498,8 +501,8 @@ static int cm32181_suspend(struct device *dev)
>  
>  static int cm32181_resume(struct device *dev)
>  {
> -	struct i2c_client *client = to_i2c_client(dev);
>  	struct cm32181_chip *cm32181 = iio_priv(dev_get_drvdata(dev));
> +	struct i2c_client *client = cm32181->client;
>  
>  	return i2c_smbus_write_word_data(client, CM32181_REG_ADDR_CMD,
>  					 cm32181->conf_regs[CM32181_REG_ADDR_CMD]);