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    SubjectRe: [RFC PATCH 1/2] i2c: Add i2c_verify_device_id() to verify device id
    On Mon, Mar 19, 2018 at 05:47:05PM +0100, Peter Rosin wrote:
    > 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?
    >
    Unfortunately it looks like only NXPs GPIO expanders and i2c muxes support
    it, or at least I didn't find any other chips. I figured though that it
    would be worth it even if only two drivers (or even one) end up using it.

    > I wonder when other manufacturers will get on board?
    >
    Hah, good question. As mentioned above, I didn't find any.

    > 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...
    >

    That would be nice. You could ask at i2c.support@nxp.com, but I guess
    it would always be somewhat risky since the standard doesn't restrict
    its use, and some product manager at NXP might decide in the future
    that a device ID of 0x00 would be "cool".

    Guenter

    > > Cc: Peter Rosin <peda@axentia.se>
    > > Signed-off-by: Guenter Roeck <linux@roeck-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 {
    > >
    >

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