[U-Boot] Regression: dm: i2c: Make i2c_get_chip_for_busnum() fail if the chip is not detected

[Heiko Schocher]

Hello Stephen,

Am 10.12.2018 um 19:23 schrieb Stephen Warren:
> The following commit:
> 
>> dm: i2c: Make i2c_get_chip_for_busnum() fail if the chip is not detected
>>     i2c_get_chip_for_busnum() really should check the presence of the chip on
>>     the bus. Most of the users of this function assume that this is done.
> 
> ... causes a boot failure on NVIDIA Jetson TX2:

:-(

Thanks for detecting so fast!

>> U-Boot 2019.01-rc1-00220-g7ff485c68b7e (Dec 10 2018 - 11:20:41 -0700)
>>
>> TEGRA186
>> Model: NVIDIA P2771-0000-500
>> DRAM:  7.8 GiB
>> tegra_ivc_read_get_next_frame() timed out (-12)
>> tegra_board_init: Cannot find MAX77620 I2C chip
>> initcall sequence 00000000fffa95a8 failed at call 0000000080083480 (err=-110)
>> ### ERROR ### Please RESET the board ###
> 
> This may be due to the fact the bus in question is implemented by RPC to a separate CPU, and that 
> mechanism hasn't been used with probing before. In general though, there's not guarantee that 
> probing will work even on a local/native I2C bus, since different chips don't support all probe 
> methods (see i2c-detect in Linux, which supports various different probing methods due to this), so 
> I'm rather surprised this change was implemented. Is it really necessary? I believe we should revert 
> it.

Hmm... yes, you are right.

Ah, Jean-Jacques first had another approach, see:

https://lists.denx.de/pipermail/u-boot/2018-October/343230.html

May it is possible to switch back to this approach ?

bye,
Heiko
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