Dear Sam,
In message CAKaJLVvL-E7b5XKqixM4yn=2rXW5qzRRS5ijkWRjmdetdakZ2Q@mail.gmail.com you wrote:
AFAIU, that behavior was changed in the mentioned patch (please see my original message). Let me elaborate a bit. In v2018.01 everything works fine and none errors/warnings are present on my boards (AM57x EVM and X15 board). The problem appears after commit fb69464eae1e ("env: Allow to build multiple environments in Kconfig"). Now U-Boot tries to load the environment from SD card first (uEnv.txt file on FAT partition), and then from eMMC partition. In case when SD card is not inserted, I observe mentioned errors. So I'm not sure how to handle this properly, that's why I created this thread... Let me try and explain my concerns better:
I think we both are talking about the same thing. I just see it differently :-)
If the user configures the system to try the SDCard first for the environment, and it cannot find it there, then this should be considered an error situation (even if recoverable by falling back to secondary storage), and at least a warning must be printed (or an error, if there is no secondary storage configured).
I agree with you that both the part about the CRC error and the part about using the default environment are wrong in this case, so the tezt of the warning message needs to be fixed - it should say clearly that the attempt to _read_ the environment from storage device _XXX_ failed.
- On the one hand, it's good to check the environment on both SD
card and eMMC (that was done in mentioned patch). This case seems to be legit (at least as far as I understand it), i.e. when SD card is not inserted, it's fine, we just check the env on eMMC
If this is what is configured, yes. In this case I would expoect to see something like this:
# Warning: Can't read environment from SDCard, trying now: eMMC.
or such [eventually - and if available - with additional information like "no card present"].
- But on the other hand, errors shouldn't appear in boot log, if
it's legit case, it's confusing the user
Well, the "legit case" is that the primary storage for the environment works. If it is not available, this is something that the user should be made aware of.
Please correct me if I'm wrong, I'm just trying to come up with correct perspective about what should be done about it. Like:
- Just disable SD card environment (i.e. revert that patch changes
for my board). But it's probably a useful feature?
It is definitely a useful feature in many situations.
On the other hand, as always you should know what you are doing. For example:
Assume no error/warning is printed when no SDCard is present. Then the user might not even be aware that the SDCard is being probed. He may assume he can secure his system for example by setting bootdelay=0 to prevent commandline access in U-Boot. And apparently this will work fine for him - until someone comes along wh inserts a SDCard with different environment settings.
I think it is a good ide to inform the user what is actually going on...
- Fix errors handling when multiple environments are enabled
THis is definitely needed, agreed.
In my case, we have two sources for the env: SD card and eMMC. And we have 2 possible state of the board:
- SD card is inserted. U-Boot will be ran from SD card
- SD card is not inserted. U-Boot will be ran from eMMC
The question is, how we are supposed to handle environment for those two cases? Right now it's being tested from SD card first, then (if not found), it's going to be tested from eMMC. That's where the error appears (if SD card is not inserted).
I think this is pretty clear: the configuration apparently selects SDCard as the primary storage for the environment and probes it first. When it is not present, it tries the second best option, eMMC. In this case a warning is appropriate. And i eMMC does not work either, then an error message must be printed.
Ok, you are saying that the error shouldn't happen. But the only way I see to change that, is to implement conditional probing for the environment. Like:
- If we are being booted from SD card, load the environment only from SD card
- If we are being booted from eMMC, load the environment only from eMMC
This is another configuration. it is as valid as the other one. I assume you can insert a SDCard without SPL/U-Boot on it, so you will still boot from eMMC, but read the environment from SDCard?
There are many configurations which could be implemented, but they all should be explicit about the "search order" for the environment.
Of course ou can make this as complicated as you like. One could also define a policy if all storage locations are equal, so you don't care where the environment is coming from as long as any of them works. Or you define a clear sequence, in which case you will want to be informed (warning) when the primary location does not work. One could even make this behavious switchable at run-time. But: do we really need that?
I would expect, that the strict order primary forst, then try next storage devices in strict sequence, and warn for not working ones, is what most users expect and find useful.
Best regards,
Wolfgang Denk