linux-kernel - Re: [RFC PATCH 1/2] i2c: Add i2c_verify_device

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Date:   Mon, 19 Mar 2018 17:47:05 +0100
From:   Peter Rosin <peda@...ntia.se>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Wolfram Sang <wsa@...-dreams.de>, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Adrian Fiergolski <adrian.fiergolski@...n.ch>
Subject: Re: [RFC PATCH 1/2] i2c: Add i2c_verify_device_id() to verify device
 id

On 2018-03-19 17:10, Guenter Roeck wrote:
> Commit dde67eb1beeb ("i2c: add i2c_get_device_id() to get the standard
> I2C device id") added a function to return the standard I2C device ID.
> Use that function to verify the device ID of a given device.

Yeah, you're moving complexity from the driver to the core, reducing
the indentation level and generally make things look neater. In fact,
I thought about adding something like this, but didn't since I only had
the one user.

The only negative is the added line count, but I suppose more drivers
will call this function down the line so it should be a net win in the
long run. There was the PCA9641 chip earlier today e.g., but maybe we
should wait for more device id users?

I wonder when other manufacturers will get on board?

I also wonder if NXP will ever release a chip with part-id 0 and
die-revision 0? If not, an all zero struct i2c_device_identity
could be used instead of manufacturer_id 0xffff and that would
simplify the pca954x driver code a bit more. But I guess we can
never know the answer to that question. And even if we did, the
answer might change later. But it would be nice...

> Cc: Peter Rosin <peda@...ntia.se>
> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> ---
> RFC:
> - Compile tested only

Can't test either since I have no chips, but the code looks good.

Adrian have HW, but maybe he's getting tried of testing?

Hmmm, for testing purposes it would be nice if a linux slave device
implemented this. But I don't have HW that supports that either so it
wouldn't help *me* anyway...

Anyway, ack from me for both patches. But maybe I'm the one
picking them up? Wolfram?

Cheers,
Peter

> - Should there also be I2C_DEVICE_PART_ID_ANY to enable maching
>   against all parts from a given manufacturer ?
> 
>  drivers/i2c/i2c-core-base.c | 34 ++++++++++++++++++++++++++++++++++
>  include/linux/i2c.h         |  3 +++
>  2 files changed, 37 insertions(+)
> 
> diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
> index 16a3b73375a6..4e4372b064f6 100644
> --- a/drivers/i2c/i2c-core-base.c
> +++ b/drivers/i2c/i2c-core-base.c
> @@ -2009,6 +2009,40 @@ int i2c_get_device_id(const struct i2c_client *client,
>  }
>  EXPORT_SYMBOL_GPL(i2c_get_device_id);
>  
> +/**
> + * i2c_verify_device_id - verify device ID
> + * @client: The device to query
> + * @id: Expected device ID
> + *
> + * Returns negative errno on error, zero on success.
> + */
> +int i2c_verify_device_id(const struct i2c_client *client,
> +			 const struct i2c_device_identity *id)
> +{
> +	struct i2c_device_identity real_id;
> +	int ret;
> +
> +	if (id->manufacturer_id == I2C_DEVICE_ID_NONE)
> +		return 0;
> +
> +	ret = i2c_get_device_id(client, &real_id);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (id->manufacturer_id != real_id.manufacturer_id ||
> +	    id->part_id != real_id.part_id ||
> +	    (id->die_revision != I2C_DEVICE_DIE_REVISION_ANY &&
> +	     id->die_revision != real_id.die_revision)) {
> +		dev_err(&client->dev, "unexpected device id %03x-%03x-%x\n",
> +			real_id.manufacturer_id, real_id.part_id,
> +			real_id.die_revision);
> +		return -ENODEV;
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(i2c_verify_device_id);
> +
>  /* ----------------------------------------------------
>   * the i2c address scanning function
>   * Will not work for 10-bit addresses!
> diff --git a/include/linux/i2c.h b/include/linux/i2c.h
> index 44ad14e016b5..45bae9717ecb 100644
> --- a/include/linux/i2c.h
> +++ b/include/linux/i2c.h
> @@ -189,6 +189,8 @@ i2c_smbus_read_i2c_block_data_or_emulated(const struct i2c_client *client,
>  					  u8 command, u8 length, u8 *values);
>  int i2c_get_device_id(const struct i2c_client *client,
>  		      struct i2c_device_identity *id);
> +int i2c_verify_device_id(const struct i2c_client *client,
> +			 const struct i2c_device_identity *id);
>  #endif /* I2C */
>  
>  /**
> @@ -216,6 +218,7 @@ struct i2c_device_identity {
>  #define I2C_DEVICE_ID_NONE                         0xffff
>  	u16 part_id;
>  	u8 die_revision;
> +#define I2C_DEVICE_DIE_REVISION_ANY		     0xff
>  };
>  
>  enum i2c_alert_protocol {
>