On 11/12/2018 05:41, Heiko Schocher wrote:
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.
The probe method is not the same in u-boot as in i2c-detect. In u-boot there is no data transfer, the probe only sends the address on the bus and fails if the device does not respond with a ACK (or if something else goes wrong). Every I2C device supports this kind of probe by design.
Errors could happen though:
- device not present, or not powered up or in reset state
- bus not ready (in your case, maybe the CPU doing the actual work is not ready)
- bus speed too high.
In all those cases this could be fixed in the board specific code.
While I agree that a commit should not break platforms, I'm not convinced that reverting the commit is the right solution: in tegra_board_init() the call to i2c_get_chip_for_busnum() is followed by a call to dm_i2c_write(). Assuming that we remove the offending commit, i2c_get_chip_for_busnum() would not fail anymore, but in this case the following call to dm_i2c_write() should fail. If it doesn't then I suspect that there is something wrong in the tegra I2C bus driver that makes it unable to transfer only the address word.
JJ
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