[U-Boot] [resent] New chapter in i.MX51 datasheet an issue?

[Stefano Babic]

On 07/05/2012 09:11, David Jander wrote:
> 
> Dear Stefano,
> 

Hi David,

> Yes, but is none of those boards using 3.15 or 3.3V? If they are, those bits
> must be cleared!

This is a good question - also because SD was tested and it is working
on these cards. I am asking to myself how it can work if voltage is wrong.

>> At the moment, we have no problems and I can explain why. The only
>> boards setting these pins (for SD card) are mx51evk and vision2. Both
>> are setting PAD_CTL_DRV_VOT_HIGH, and because the define is wrong, they
>> are really setting the pin to low output voltage mode.
> 
> AFAIK, most SD-cards need 3.1V or more to work, and the EVK boots from an SD
> card. That means, the rails NVCC_PER15 and/or NVCC_PER17 are probably powered
> from a 3.15 or 3.3V supply, so the HVE bits for those pins must be cleared in
> able to avoid damage (3.3V is what they call "Ultra High Voltage").

Really I have expected that SD does not work if the voltage is lower as
specified, not that theree is a damage - I can understand this in the
opposite case (setting high voltage when low voltage is required).

>> For other boards and other pins, voltage is not explicitely set : this
>> means they work in low voltage mode after a reset.
> 
> Everyone reading the documentation as it was available before 03-2012 would
> most probably think this is ok, even for 3.1...3.6V powered pins, but according
> to the new documentation, it isn't. So probably many boards need to be
> re-designed or at least u-boot board-code needs to be fixed for them. This is
> a different issue though, and needs to be addressed by the different BSP
> maintainers or board manufacturers.

I think only u-boot code should be fixed.

> 
>> To fix arch/arm/include/asm/arch-mx5/iomux.h and synchronize it with the
>> documentation, we need also to change mx51evk / vision2, setting the
>> pins to PAD_CTL_DRV_VOT_LOW, and they will work as now.
> 
> ... and probably die.

well, they will work as now - with low voltage instead of high voltage.
Anyway, I agree that this should be wrong, because when the code was
written was thought that the voltage should be high.

> The setting is most probably wrong. All we need to do,
> is change the define in the header files, and not touch the mx51evk / vision2
> BSP files. But the respective maintainers need to be warned IMHO.

Go ahead in this direction. Then we can test on these boards (mx51evk /
vision2 / efikamx), the only ones having these issue).

Best regards,
Stefano Babic


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