linux-kernel - Re: [RFC PATCH v2 6/6] i2c: core: hand over reserved devices when requesting ancillary addresses

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Message-ID: <610bbd01-e245-3320-c315-7a5c945a700d@lucaceresoli.net>
Date:   Wed, 15 Apr 2020 12:07:24 +0200
From:   Luca Ceresoli <luca@...aceresoli.net>
To:     Wolfram Sang <wsa+renesas@...g-engineering.com>,
        linux-i2c@...r.kernel.org
Cc:     linux-renesas-soc@...r.kernel.org, linux-i3c@...ts.infradead.org,
        Kieran Bingham <kieran@...uared.org.uk>,
        Niklas Söderlund <niklas.soderlund@...natech.se>,
        Jacopo Mondi <jacopo@...ndi.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Vladimir Zapolskiy <vz@...ia.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 6/6] i2c: core: hand over reserved devices when
 requesting ancillary addresses

Hi,

On 18/03/20 16:00, Wolfram Sang wrote:
> With i2c_new_ancillary_address, we can check if the intended driver is
> requesting a reserved address. Update the function to do these checks.
> If the check passes, the "reserved" device will become a regular "dummy"
> device.
> 
> Signed-off-by: Wolfram Sang <wsa+renesas@...g-engineering.com>
> ---
>  drivers/i2c/i2c-core-base.c | 24 ++++++++++++++++++++++--
>  1 file changed, 22 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
> index 84464e439df5..81fb320de28d 100644
> --- a/drivers/i2c/i2c-core-base.c
> +++ b/drivers/i2c/i2c-core-base.c
> @@ -974,7 +974,9 @@ struct i2c_client *i2c_new_ancillary_device(struct i2c_client *client,
>  						const char *name,
>  						u16 default_addr)
>  {
> -	struct device_node *np = client->dev.of_node;
> +	struct device_node *reserved_np, *np = client->dev.of_node;
> +	struct device *reserved_dev, *adapter_dev = &client->adapter->dev;
> +	struct i2c_client *reserved_client = NULL;
>  	u32 addr = default_addr;
>  	int i;
>  
> @@ -984,7 +986,25 @@ struct i2c_client *i2c_new_ancillary_device(struct i2c_client *client,
>  			of_property_read_u32_index(np, "reg", i, &addr);
>  	}
>  
> -	dev_dbg(&client->adapter->dev, "Address for %s : 0x%x\n", name, addr);
> +	dev_info(adapter_dev, "Address for %s : 0x%x\n", name, addr);

Here if we have two identical chips on the same bus, they probably will
both add an ancillary device with the same name. Then a message like:

  i2c i2c-0: ds90ub954-q1: Address for rxport0: 0x40

won't tell which ds90ub954-q1 device is using that address. I'd rather
disambiguate using something like:

  dev_info(adapter_dev, "%s: Address for %s: 0x%x\n",
           dev_name(&client->dev), name, addr);

Sure, this issue did exist before this patch, but since the line is
being promoted from dbg to info (which is OK), it's probably a good idea
to improve the content, perhaps in a separate patch.

Except for that, I tested the patch and it's working fine.

-- 
Luca