Re: [lm-sensors] [PATCH] hwmon: (pmbus) Fix two issues

[Guenter Roeck <guenter.roeck@ericsson.com>]

On Mon, Nov 14, 2011 at 09:35:44PM -0500, Tang Yuantian-B29983 wrote:
> Hi Jean Delvare,
> 
> Please find my comments in line.
> 
> > -----Original Message-----
> > 
> > Again, no. PMBus goes on top of SMBus which includes SMBus block reads
> > (i2c_smbus_read_block_data) but not I2C block reads
> > (i2c_smbus_read_i2c_block_data). As a result, many hardware SMBus
> > controllers do not support I2C block reads, and it can't be added (only
> > the set of transfers supported by the hardware controller can be
> > implemented by the driver) which means that your proposed change would
> > break support on existing systems. This is not acceptable.
> > 
> > On the other hand, an I2C controller which supports I2C block reads can
> > almost always get SMBus block reads added, it's only a matter of adding a
> > few lines of code to the bus driver.
> > 
> > Which i2c bus driver are you using? From which kernel version?
> > 
> [Yuantian:] I am using newest kernel 3.2. PowerPC arch. 
> I2c bus driver file is: drivers/i2c/busses/i2c-mpc.c.
> 
> I greped the i2c bus driver and found the following platform's i2c don't 
> Support i2c_smbus_read_block_data. So Zl6100 driver can't work on these platforms.
> 1. drivers/i2c/busses/i2c-mpc.c(powerpc arch, which I am working on).
> 2. drivers/i2c/busses/i2c-mv64xxx.c
> 3. drivers/i2c/busses/i2c-nomadik.c
> 4. drivers/i2c/busses/i2c-octeon.c
> 5. drivers/i2c/busses/i2c-pxa.c
> 6. drivers/i2c/busses/i2c-s6000.c
> Almost all the platforms the kernel support.
> But they all support I2C_FUNC_SMBUS_EMUL, which means support i2c_smbus_read_i2c_block_data.

Hmm ... looking into the code, I2C_FUNC_SMBUS_READ_BLOCK_DATA is missing from I2C_FUNC_SMBUS_EMUL.
Now that is interesting.

If you change mpc_functionality() to
	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL | I2C_FUNC_SMBUS_READ_BLOCK_DATA;
I bet your problem will disappear.

Jean, any idea why I2C_FUNC_SMBUS_EMUL doesn't include I2C_FUNC_SMBUS_READ_BLOCK_DATA ?

Thanks,
Guenter


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