[U-Boot] [RFC PATCH 2/2] dm: i2c: support 10bit addressing in I2C uclass layer

[Masahiro YAMADA]

Hi Simon,


2014-12-20 6:34 GMT+09:00 Simon Glass <sjg at chromium.org>:
> Hi Masahiro,
>
> On 19 December 2014 at 11:34, Masahiro Yamada <yamada.m at jp.panasonic.com> wrote:
>> Master send to / receive from 10-bit addressed slave devices
>> can be supported by software layer without any hardware change
>> because the LSB 8bit of the slave address is treated as data part.
>>
>> Master Send to a 10bit-addressed slave chip is performed like this:
>>
>>  DIR    Format
>>  M->S   11110 + address[9:8] + R/W(0)
>>  M->S   address[7:0]
>>  M->S   data0
>>  M->S   data1
>>       ...
>>
>> Master Receive from a 10bit-addressed slave chip is like this:
>>
>>  DIR    Format
>>  M->S   11110 + address[9:8] + R/W(0)
>>  M->S   address[7:0]
>>         (Restart)
>>  M->S   111110 + address[9:8] + R/W(1)
>>  S->M   data0
>>  S->M   data1
>>       ...
>>
>> Signed-off-by: Masahiro Yamada <yamada.m at jp.panasonic.com>
>> Cc: Heiko Schocher <hs at denx.de>
>> Cc: Simon Glass <sjg at chromium.org>
>> ---
>>
>>  drivers/i2c/i2c-uclass.c | 80 +++++++++++++++++++++++++++++++-----------------
>>  include/i2c.h            |  4 +++
>>  2 files changed, 56 insertions(+), 28 deletions(-)
>
> Seems like a good idea if we can make it work...
>
> But this is driver-specific. Some drivers have hardware to send the
> address and it isn't part of the message. For example see the tegra
> driver.
>
> So what you have here feels a bit like a hack to me. Can't the driver
> implement it? If you are trying to avoid driver work to support 10-bit
> addresses, maybe it should be an option that we can enable for each
> driver, so we don't break the other drivers?


I was writing two I2C drivers on DM,
both of which have no dedicated hardware support for 10bit addressing.

Of course, the driver could implement it, but it means
I put the completely the same code in each of driver.

For write transaction, for example, we create a new buffer and copy
offset-address + data in Uclass layer.

Do I have to create a new buffer again, in my driver,
and copy  lower-slave-address + offset-address + data ?

Perhaps, is it a good idea to have it optional?

DM_I2C_FLAG_SW_TENBIT  - if set, uclass takes care of 10bit addressing
by software
                                                    if unset, each
driver is responsible to handle I2C_M_TEN correctly

altough I do think 10bit support on U-Boot is urgent necessity...




-- 
Best Regards
Masahiro Yamada