topic Re: clock frequency of sdio in u-boot & linux in i.MX Processors

clock frequency of sdio in u-boot & linux

rans — Thu, 10 Nov 2016 20:30:31 GMT

Hello,

In linux device tree there is configuration for sdio clock-frequency:

&usdhc2 {

pinctrl-names = "default";

pinctrl-0 = <&pinctrl_usdhc2_2>;

no-1-8-v;

bus-width = <4>;

clock-frequency = <40000000>;

max-frequency = <40000000>;

keep-power-in-suspend;

enable-sdio-wakeup;

status = "okay";

};

But in u-boot I don't find such configuration, so I wander, how is it that u-boot can manage working with sdio in a slower rate, while linux need to be configured for that rate in device tree ?

Thank you,

Ran

Re: clock frequency of sdio in u-boot & linux

igorpadykov — Thu, 10 Nov 2016 23:41:33 GMT

Hi Ran

seems uboot uses rom boot usdhc settings described in

sect.8.5.3.1 Expansion Device eFUSE Configuration i.MX6DQ

Reference Manual

http://cache.freescale.com/files/32bit/doc/ref_manual/IMX6DQRM.pdf

Best regards
igor
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Re: clock frequency of sdio in u-boot & linux

rans — Fri, 11 Nov 2016 07:54:49 GMT

Hi Igor,

Thank you,

I have a strange issue where I can access mmc from u-boot (mmc commands), but not from linux.

Not sure yet, why. It is a new board design. older design worked very well.

If the failure was both in u-boot and linux, it was easier, and we could tell is it a HW issue.

But since from u-boot is seems to work, we are not sure.

Regards,

Ran

Re: clock frequency of sdio in u-boot & linux

igorpadykov — Fri, 11 Nov 2016 08:04:23 GMT

this may be due to drive strength and associated with it

signal integrity issues, in *dts file one can check for example:

        pinctrl_usdhc3: usdhc3grp {
           fsl,pins = <
               MX6QDL_PAD_SD3_CMD__SD3_CMD       0x17059
               MX6QDL_PAD_SD3_CLK__SD3_CLK       0x10059

which corresponds to register IOMUXC_SW_PAD_CTL_PAD_SD3_CLK,

one can tweak DSE settings

Best regards
igor