linux-kernel - Re: [PATCH] iio: proximity: lidar-v2: replace i2c block access method with the one already implemented.

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Message-ID: <20180914014806.GA25667@Eros>
Date:   Fri, 14 Sep 2018 09:48:06 +0800
From:   Song Qiang <songqiang1304521@...il.com>
To:     Matt Ranostay <matt.ranostay@...sulko.com>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: proximity: lidar-v2: replace i2c block access
 method with the one already implemented.

On Thu, Sep 13, 2018 at 02:43:35PM -0700, Matt Ranostay wrote:
> On Wed, Sep 12, 2018 at 8:51 PM Song Qiang <songqiang1304521@...il.com> wrote:
> >
> > This driver tries to access a block of data on a i2c bus and it tries
> > to manually make a device command frame and a consecutively read frame,
> > then uses i2c_transfer() to read data. But this has already been
> > implemented in i2c_smbus_read_i2c_block_data().
> > Sorry for not having this device by my hand, which is a little expansive
> > for me, but I have another i2c device and tested with both i2c_transfer()
> > and i2c_smbus_read_i2c_block_data() and they all ends the same.
> > I'm not familiar with the SMBus, don't know if the lidar_smbus_xfer()
> > function is the same as i2c_smbus_read_block_data()? The original code
> > is commented with something I'm not sure, but I think if it's a standard
> > SMBus, it should be able to use in here.
> > Hoping for someone to explain.
> >
> 
> Yes actually there is a reason for this insanity!
> 
> It isn't actually SMBUS (note the lidar_smbus_xfer function below it)
> and has a odd way to read registers via I2C.
> Basically the I2C_M_STOP flags is the reason you can use the standard
> i2c_smbus_read_i2c_block_data().
> 
> Page 6 in this datasheet
> * http://static.garmin.com/pumac/LIDAR_Lite_v3_Operation_Manual_and_Technical_Specifications.pdf
> 
> > Signed-off-by: Song Qiang <songqiang.1304521@...il.com>
> > ---
> >  .../iio/proximity/pulsedlight-lidar-lite-v2.c  | 18 +-----------------
> >  1 file changed, 1 insertion(+), 17 deletions(-)
> >
> > diff --git a/drivers/iio/proximity/pulsedlight-lidar-lite-v2.c b/drivers/iio/proximity/pulsedlight-lidar-lite-v2.c
> > index 47af54f14756..ca880ba8e820 100644
> > --- a/drivers/iio/proximity/pulsedlight-lidar-lite-v2.c
> > +++ b/drivers/iio/proximity/pulsedlight-lidar-lite-v2.c
> > @@ -63,23 +63,7 @@ static const struct iio_chan_spec lidar_channels[] = {
> >
> >  static int lidar_i2c_xfer(struct lidar_data *data, u8 reg, u8 *val, int len)
> >  {
> > -       struct i2c_client *client = data->client;
> > -       struct i2c_msg msg[2];
> > -       int ret;
> > -
> > -       msg[0].addr = client->addr;
> > -       msg[0].flags = client->flags | I2C_M_STOP;
> > -       msg[0].len = 1;
> > -       msg[0].buf  = (char *) &reg;
> > -
> > -       msg[1].addr = client->addr;
> > -       msg[1].flags = client->flags | I2C_M_RD;
> > -       msg[1].len = len;
> > -       msg[1].buf = (char *) val;
> > -
> > -       ret = i2c_transfer(client->adapter, msg, 2);
> > -
> > -       return (ret == 2) ? 0 : -EIO;
> > +       return i2c_smbus_read_i2c_block_data(data->client, reg, len, val);
> >  }
> >
> >  static int lidar_smbus_xfer(struct lidar_data *data, u8 reg, u8 *val, int len)
> > --
> > 2.17.1
> >

Hi Matt,

Thanks for the explanition, now I understand why we have to use
lidar_smbus_xfer() here.
So we can use the standard i2c_smbus_read_i2c_block_data() here?
I'm thinking since you are the author it seems like you have the
hardware, would you mind to test if it's working? I'd appriciate
that.

yours,
Song Qiang