I.MX8 MMC clock rate and bus-width customisation in Linux

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I.MX8 MMC clock rate and bus-width customisation in Linux

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liamjm36
Contributor II

Hey,

I am relatively new to Embedded Linux development but have not been able to find answers elsewhere. 

How can I change the clock speeds and bus width of the mmc device? We are using an SD card multiplexer which has been tested and works when clocked at 16 MHz for SDIO. However I cannot get it to be recognised in Linux. When mounted directly SD cards are recognised. Running the following terminal command I found that the card was being read from a 208 MHz clock. 

/sys/kernel/debug/mmc1# cat clock

 

I would like to be able to lower the maximum MMC clock rates and optionally being able to select 1 bit SDIO instead of 4. 

 

Thanks,

Liam

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igorpadykov
NXP Employee
NXP Employee
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igorpadykov
NXP Employee
NXP Employee

Hi Liam

 

one can look at general linux mmc documentation

https://source.codeaurora.org/external/imx/linux-imx/tree/Documentation/devicetree/bindings/mmc/mmc-...

 

Best regards
igor

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