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SubjectRe: [PATCH] Revert "Staging: iio: adt7316: Add an extra check for 'ret' equals to 0"
On Wed, Dec 05, 2018 at 02:59:53PM -0700, Jeremy Fertic wrote:
> On Thu, Dec 06, 2018 at 01:25:55AM +0530, Shreeya Patel wrote:
> > On Tue, 2018-12-04 at 18:49 -0700, Jeremy Fertic wrote:
> > > This reverts commit 00426e99789357dbff7e719a092ce36a3ce49d94.
> > >
> > > i2c_smbus_read_byte() returns 0 when a byte with the value 0 is read
> > > from
> > > the device. This is a valid read so revert the check for 0.
> > >
> > > Signed-off-by: Jeremy Fertic <jeremyfertic@gmail.com>
> > > ---
> >
> > Hi Jeremy,
> >
> > As per my understanding, 0 value indicates no error but no data read.
> > Then how can this be a valid case?
> >
> > Can you please make me understand that how can we consider this as a
> > valid case even when no data has been read?

It's not reading no data. It's reading one byte of data and returning
it.

> >
> >
> > Thanks
>
> I'm not sure I understand why the value 0 would indicate no data read.
> Doesn't that just mean a byte was read with the value 0.

Yes. It does mean that. Please don't ask rhetorical questions... :(
This list is full of people who can't resist answering every question.

> For instance, if the input to the adc is 0V. Can you point me to where
> you're seeing that this would indicate no data read?

drivers/i2c/i2c-core-smbus.c
88 /**
89 * i2c_smbus_read_byte - SMBus "receive byte" protocol
90 * @client: Handle to slave device
91 *
92 * This executes the SMBus "receive byte" protocol, returning negative errno
93 * else the byte received from the device.
94 */
95 s32 i2c_smbus_read_byte(const struct i2c_client *client)
96 {
97 union i2c_smbus_data data;
98 int status;
99
100 status = i2c_smbus_xfer(client->adapter, client->addr, client->flags,
101 I2C_SMBUS_READ, 0,
102 I2C_SMBUS_BYTE, &data);
103 return (status < 0) ? status : data.byte;
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
104 }
105 EXPORT_SYMBOL(i2c_smbus_read_byte);

You are right. Commit 00426e997893 ("Staging: iio: adt7316: Add an
extra check for 'ret' equals to 0") needs to be reverted...

regards,
dan carpenter


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