CS4279 and hw_read_t/hw_write_t

CS4279 and hw_read_t/hw_write_t

[Jon Smirl]

>From soc/codecs/cs4270.c...

 *
 * Note that we don't use the hw_write function pointer of snd_soc_codec.
 * That's because it's too clunky: the hw_write_t prototype does not match
 * i2c_smbus_write_byte_data(), and it's just another layer of overhead.
 */

The prototype doesn't match because you are using
i2c_smbus_write_byte_data() instead of
i2c_master_send()/i2c_master_recv().


-- 
Jon Smirl
jonsmirl@gmail.com

Re: CS4279 and hw_read_t/hw_write_t

[Timur Tabi]

Jon Smirl wrote:
> From soc/codecs/cs4270.c...
> 
>  *
>  * Note that we don't use the hw_write function pointer of snd_soc_codec.
>  * That's because it's too clunky: the hw_write_t prototype does not match
>  * i2c_smbus_write_byte_data(), and it's just another layer of overhead.
>  */
> 
> The prototype doesn't match because you are using
> i2c_smbus_write_byte_data() instead of
> i2c_master_send()/i2c_master_recv().

Should I be using i2c_master_send() instead?  I remember reading somewhere that
I should be using the i2c smbus functions if possible.

-- 
Timur Tabi
Linux kernel developer at Freescale

Re: CS4279 and hw_read_t/hw_write_t

[Jon Smirl]

On 7/21/08, Timur Tabi <timur@freescale.com> wrote:
> Jon Smirl wrote:
>  > From soc/codecs/cs4270.c...
>  >
>  >  *
>  >  * Note that we don't use the hw_write function pointer of snd_soc_codec.
>  >  * That's because it's too clunky: the hw_write_t prototype does not match
>  >  * i2c_smbus_write_byte_data(), and it's just another layer of overhead.
>  >  */
>  >
>  > The prototype doesn't match because you are using
>  > i2c_smbus_write_byte_data() instead of
>  > i2c_master_send()/i2c_master_recv().
>
>
> Should I be using i2c_master_send() instead?  I remember reading somewhere that
>  I should be using the i2c smbus functions if possible.

i2c_smbus... will work with either a smbus controller or an i2c
controller. Inside the routine it decides which type of controller and
then ends up calling i2c_master....

You're on an i2c bus, no need to the overhead.

You'd have to read the CS4270 datasheet in detail to see if can even
be hooked up to an smbus controller. smbus is a subset of full i2c.

>
>
>  --
>  Timur Tabi
>  Linux kernel developer at Freescale
>


-- 
Jon Smirl
jonsmirl@gmail.com

Re: CS4279 and hw_read_t/hw_write_t

[Timur Tabi]

Jon Smirl wrote:

> You'd have to read the CS4270 datasheet in detail to see if can even
> be hooked up to an smbus controller. smbus is a subset of full i2c.

There's no mention of SM Bus anywhere in the CS4270 datasheet.  Can I assume
that it won't work?

I remember now trying to use a standard I2C-only function and it didn't work,
but that was a long time ago before I knew much about the hardware.  I'll have
to try it again.

-- 
Timur Tabi
Linux kernel developer at Freescale

Re: CS4279 and hw_read_t/hw_write_t

[Jon Smirl]

On 7/21/08, Timur Tabi <timur@freescale.com> wrote:
> Jon Smirl wrote:
>
>  > You'd have to read the CS4270 datasheet in detail to see if can even
>  > be hooked up to an smbus controller. smbus is a subset of full i2c.
>
>
> There's no mention of SM Bus anywhere in the CS4270 datasheet.  Can I assume
>  that it won't work?

SMBus devices will work on an i2c controller. But i2c devices won't
always work on a smbus controller. i2c is a superset of smbus, it can
do things smbus can't.

SMbus (system management bus) is usually used for simple things like
fan and temperature monitors.

>From wikipedia on i2c:
"Pure I²C systems support arbitrary message structures. SMBus is
restricted to nine of those structures, such as "read word N" and
"write word N", involving a single slave."


>
>  I remember now trying to use a standard I2C-only function and it didn't work,
>  but that was a long time ago before I knew much about the hardware.  I'll have
>  to try it again.
>
>
>  --
>
> Timur Tabi
>  Linux kernel developer at Freescale
>


-- 
Jon Smirl
jonsmirl@gmail.com