Re: [PATCH v2] i2c: stub: Add support for SMBus block commands

[Guenter Roeck]

Hi Jean,

On 07/08/2014 12:54 PM, Jean Delvare wrote:
> Hi Guenter,
>
> On Mon,  7 Jul 2014 07:23:03 -0700, Guenter Roeck wrote:
> > SMBus block commands are different to I2C block commands since
> > the returned data is not normally accessible with byte or word
> > commands on other command offsets. Add linked list of 'block'
> > commands to support those commands.
> >
> > Access mechanism is quite simple: Block commands must be written
> > before they can be read. The first write selects the block length.
> > Subsequent writes can be partial. Block read commands always return
> > the number of bytes selected with the first write.
> >
> > Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > ---
> > v2: Make new functionality only available on request via functionality
> >      module parameter
> >      Add more details about SMBus block mode support to documentation
> >      Use correct sizeof() variable in devm_kzalloc
> >      Use stub_find_block() only in SMBus block command itself.
> >      Store first word of block data in chip->words[].
> >      When writing block data and the written data is longer than
> >      the first write, bail out with debug message indicating the reason
> >      for the error.
>
> Looks good, thanks for the quick update.
>
> Reviewed-by: Jean Delvare <jdelvare@xxxxxxx>
>
> Just one thing I have been thinking about while reviewing the updated
> code... You decided to make the first SMBus block write select the
> maximum block length, and you always use that for SMBus block reads.
> However you accept partial writes. The fact that the order in which
> writes are performed has an effect on which writes are accepted is
> somewhat unexpected.
>
> Wouldn't it make more sense to accept all SMBus block writes,
> regardless of the size (as long as it is within the limits of the SMBus
> standard, of course)? Then the only thing left to decide is whether
> SMBus block reads use the maximum size or the size of the most recent
> SMBus block write.
>
> I suspect this would mimic the behavior of real chips better. What do
> you think?

Not really sure what the expected behavior is. My original code
accepted all writes and returned the most recent write, including
the most recent write length. I thought this was untypical, and that
it would be more typical for the chip to return a fixed length.
But ultimately I don't really know, and I am fine either way.

Guenter

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