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List:       linux-i2c
Subject:    Re: I2C driver modification for BH1710FVC Ambient Light Sensor
From:       Jean Delvare <khali () linux-fr ! org>
Date:       2010-08-30 15:58:36
Message-ID: 20100830175836.65260450 () hyperion ! delvare
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Hi Rogério,

On Mon, 30 Aug 2010 12:33:26 -0300, Rogério de Souza Moraes wrote:
> Hi folks,
> 
> I am developing a driver for the Ambient Light Sensor BH1710FVC that
> communicates by i2c bus. My problem is that the type of message that
> this chip accept is this:
> 
> S Addr Rd [A] [DataHigh] A [DataLow] NA P
> 
> I searched in the file "Documentation/i2c/smbus-protocol" for one
> function that communicate like this, but I did not find. I tried to
> use the function i2c_smbus_read_byte twice (reading data high first
> and so the data low), but the chip do not accept communicate this way.
> 
> So I've based in the function i2c_smbus_read_byte to build the
> function that implements the protocol like I need.
> 
> I modified the file i2c-core.c in the function i2c_smbus_xfer_emulated
> creating an I2C_SMBUS_WORD.
> In first switch I add:
> 
>         case I2C_SMBUS_WORD:
>                 if (read_write == I2C_SMBUS_READ) {
>                         msg[0].len = 2;
>                         msg[0].flags = I2C_M_RD | flags;
>                         num = 1;
>                 }
>                 break;
> 
> and for the second switch I added the following case:
> 
>                         case I2C_SMBUS_WORD:
>                                 data->word = msgbuf0[0] | (msgbuf0[1] << 8);
>                                 break;
> 
> After this modification my Ambient Light Sensor driver is working just fine.
> 
> So I want to know if there is a better way to implement this without
> need to modify the i2c driver.

As the transaction format you need isn't part of SMBus, I assume that
your controller is an I2C master and you should simply use
i2c_master_recv() in your device driver.

-- 
Jean Delvare
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