Limit mmc0 and mmc1 clock frequency

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1

I’m trying to limit mmc clock frequency by adding the line to a .dts (kernel 4.4.16-ti-rt):

max-frequency = <25000000>;

It works only for mmc2, but not for mmc0 and mmc1.
It remains 50Mhz for mmc0 and 52Mhz for mmc1.

Thanks for ideas!

2

pretty sure that get's overriden when the mmc core probes the
eMMC/microSD.. So if you really want to disable 50/52Mhz you'll have
to disable the actual sd transfer modes..

see for example on the x15, since we don't have a dual voltage
regulator, these modes must be removed:

https://github.com/RobertCNelson/dtb-rebuilder/blob/4.4-ti/src/arm/am57xx-beagle-x15.dts#L109-L113

Regards,

3

Thanks, Robert!

However, just adding that block of “delete-property”-s from the example you pointed to didn’t help.

By the way, where are those modes defined?

sd-uhs-sdr104
sd-uhs-sdr50
sd-uhs-ddr50
sd-uhs-sdr25
sd-uhs-sdr12

4

Thanks, Robert!

However, just adding that block of "delete-property"-s from the example you
pointed to didn't help.

Correct it was an "example" of how to disable modes, as the ip on the
am335x doesn't even support those... :wink:

By the way, where are those modes defined?

sd-uhs-sdr104
sd-uhs-sdr50
sd-uhs-ddr50
sd-uhs-sdr25
sd-uhs-sdr12

Here's the full list:

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/mmc/mmc.txt

Regards,

5

Thanks, Robert!

It works. Of course, it didn’t, when trying for first time I “deleted” all those modes.
The following lines successfully set MMC clock to 25MHz:

max-frequency = <25000000>;
/delete-property/ sd-uhs-sdr104;
/delete-property/ sd-uhs-sdr50;
/delete-property/ sd-uhs-ddr50;


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Sergey