linux-kernel - Re: [PATCH] mfd: da9063: occupy second I2C address, too

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Date:   Thu, 20 Jun 2019 09:07:40 +0000
From:   Steve Twiss <stwiss.opensource@...semi.com>
To:     "wsa+renesas@...g-engineering.com" <wsa+renesas@...g-engineering.com>
CC:     "bgolaszewski@...libre.com" <bgolaszewski@...libre.com>,
        "kieran.bingham+renesas@...asonboard.com" 
        <kieran.bingham+renesas@...asonboard.com>,
        "lee.jones@...aro.org" <lee.jones@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        "peda@...ntia.se" <peda@...ntia.se>,
        Support Opensource <Support.Opensource@...semi.com>
Subject: Re: [PATCH] mfd: da9063: occupy second I2C address, too

(resend because the e-mail client added HTML formatting to my last reply)

Hi Wolfram,

On Wed, 19 Jun 2019 19:18:06, Wolfram Sang wrote:

> Subject: [PATCH] mfd: da9063: occupy second I2C address, too
> 
> Even though we don't use it yet, we should mark the second I2C address
> this device is listening to as used.

Sure. There is a second method for accessing higher pages of registers.
The DA9063 Datasheet Revision 2.2, 12-Mar-2019, page 96, says this:

In 2-WIRE operation, the DA9063 offers an alternative method to access register pages 2 and 3.
These pages can be accessed directly by incrementing the device address by one (default read
address 0xB3; write address 0xB2). This removes the need to write to the page register before
access to pages 2 and 3, thus reducing the traffic on the 2-WIRE bus.

Is this a safety clause? What I mean is, shouldn't the hardware design make
sure there are not two devices located on the same I2C bus with the same slave
address?

Regards,
Steve

> Signed-off-by: Wolfram Sang <wsa+renesas@...g-engineering.com>
> Reviewed-by: Peter Rosin <peda@...ntia.se>
> Reviewed-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
> Reviewed-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
> ---
>  drivers/mfd/da9063-i2c.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/mfd/da9063-i2c.c b/drivers/mfd/da9063-i2c.c
> index 455de74c0dd2..2133b09f6e7a 100644
> --- a/drivers/mfd/da9063-i2c.c
> +++ b/drivers/mfd/da9063-i2c.c
> @@ -221,6 +221,8 @@ static int da9063_i2c_probe(struct i2c_client *i2c,
>  		return ret;
>  	}
>  
> +	devm_i2c_new_dummy_device(&i2c->dev, i2c->adapter, i2c->addr + 1);
> +
>  	return da9063_device_init(da9063, i2c->irq);
>  }
>  
> -- 
> 2.20.1