IM6Q_SDHCI_HOST_CONTROL2

[thouswave]

In the linux-3.0.35 sd driver.

File:sdhci.c

Func:sdhci_start_signal_voltage_switch

Reg:SDHCI_HOST_CONTROL2(#define SDHCI_HOST_CONTROL2 0x3E)

From the datasheet,0x3E is part of the retgister uSDHC1_AUTOCMD12_ERR_STATUS,it is a readonly erea.But,the linux kernel source has the write operation:

sdhci_writew(host, ctrl, SDHCI_HOST_CONTROL2);

Question:

1.Is there some problem with register write to SDHCI_HOST_CONTROL2(0x3E)

2.The function sdhci_start_signal_voltage_switch can be used to switch signal voltage from 3.3V to 1.8V for UHS card,If SDHCI_HOST_CONTROL2 can be write,it seems no affect to the signal voltage.

3.I also check the source in u-boot.In u-boot,when use a UHS card,the source write register uSDHCx_VEND_SPEC bit 1:

          Voltage Selection

               Change the value of output signal VSELECT, to control the voltage on pads for external card. There must be a control circuit out of uSDHC to change the voltage on pads.

              1 Change the voltage to low voltage range, around 1.8V

              0 Change the voltage to high voltage range, around 3.0V

So I think u-boot source is right,the kernel may be wrong ,is that right?

[alejandrolozan1 · Accepted solution]

Hi, please see my comments below:

1) sdhci.c is generickernel driver is not the i.mx sdhc driver.

2) SDHCI_HOST_CONTROL is not a hardware register offset .

3) sdhci_writew is a calback to the platform write function, the one defined in the driver.

4) sdhci-esdhc-imx.c is the real driver which in his write_w function handles properly the

    SDHCI_HOST_CONTROL2 to te real offset in the hardware.

I hope this helps.

Regards,

Alejandro

[thouswave]

Thanks very much.