iMX6 - CPU frequency lowered during LDO bypass setting

[Ansari]

Hi,

We are using imx6Q sabresd platform for our development with Linux 3.14.28_1.0.0-GA BSP but initially we used Linux 3.10.17_1.0.0-GA BSP.

We have gone through below files from Linux 3.14.28_1.0.0-GA(File-1) and Linux 3.10.17_1.0.0-GA (FIle-2) BSPs.

File-1: ~/u-boot-imx/board/freescale/mx6sabresd/mx6sabresd.c

File-2: ~/u-boot-imx/board/freescale/mx6qsabresd/mx6qsabresd.c

We could see some changes are added in File-1(compare to File-2).

In below function, we understood that the CPU frequency is lowered to 400Mhz before doing the LDO bypass and CPU frequency is increased to 800Mhz after the LDO bypass settings.

"ldo_mode_set"

In FIle-2 (Linux 3.10.17_1.0.0-GA), the below function will do the LDO bypass settings without changing the CPU frequency.

"ldo_mode_set"

We would like to know, during the LDO bypass settings why the CPU frequency is lowered in File-1(Linux 3.14.28_1.0.0-GA)?  Is it recommended  to do the same.?

Thank You,

Regards,

Ansari

[Ansari]

Dear Igor and Andrea,

Thank you for your valuable inputs.

Regards,

Ansari

[igorpadykov]

Hi Abdul

CPU frequencylowering during the LDO bypass is not requirement,

but it provides less power spikes, so gives more board stability.

Best regards

igor

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[andreascian · Accepted solution]

Dear Igor,

by looking inside u-boot code and the commits from FSL engineer, it seems that the older implementation is a violation of datasheet power constraint

I've search for some details inside the code/datasheet and I found the some information I sent to Abdul in meta-freescale mailing list:

https://lists.yoctoproject.org/pipermail/meta-freescale/2015-April/013447.html

WDYT about that?

Kind Regards,

Andrea

[igorpadykov]

Hi Andrea

I think these considerations are quite reasonable.

Best regards

igor