UHS-1 cards with iMX6Q

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

Hi,

I have a Samsung 8GB UHS-1 card which I'm trying with iMX6Q, and it's
not behaving very well with the voltage switch.  With MMC debugging
enabled - and augmented with additional debug for the ESDHC_VENDOR
register, I'm seeing this with 3.14-rc1:

[    2.771270] mmc1: starting CMD11 arg 00000000 flags 00000015
[    2.771575] sdhci [sdhci_irq()]: *** mmc1 got interrupt: 0x00000080
[    2.771613] sdhci [sdhci_irq()]: *** mmc1 got interrupt: 0x00000001
[    2.771632] mmc1: req done (CMD11): 0: 00000320 00000000 00000000 00000000
[    2.772669] mmc1: clock 0Hz busmode 2 powermode 2 cs 0 Vdd 21 width 0 timing 0
[    2.772679] mmc1: clearing ESDHC_VENDOR_SPEC_FRC_SDCLK_ON
[    2.772687] mmc1: ESDHC_VENDOR_SPEC_VSELECT is clear
[    2.772695] mmc1: clearing ESDHC_VENDOR_SPEC_VSELECT
[    2.772703] mmc1: clearing ESDHC_VENDOR_SPEC_FRC_SDCLK_ON
[    2.772713] sdhci-esdhc-imx 2194000.usdhc: change pinctrl state for uhs 0
[    2.772719] mmc1: clearing ESDHC_VENDOR_SPEC_FRC_SDCLK_ON
[    2.772729] mmc1: ESDHC_VENDOR_SPEC_VSELECT is clear
[    2.772735] mmc1: setting ESDHC_VENDOR_SPEC_VSELECT
[    2.778276] mmc1: ESDHC_VENDOR_SPEC_VSELECT is sett
[    2.786482] mmc1: clock 400000Hz busmode 2 powermode 2 cs 0 Vdd 21 width 0 timing 0
[    2.786502] sdhci-esdhc-imx 2194000.usdhc: desired SD clock: 400000, actual: 386718
[    2.786511] mmc1: setting ESDHC_VENDOR_SPEC_FRC_SDCLK_ON
[    2.787515] mmc1: ESDHC_VENDOR_SPEC_VSELECT is sett
[    2.787522] mmc1: setting ESDHC_VENDOR_SPEC_VSELECT
[    2.787529] mmc1: clearing ESDHC_VENDOR_SPEC_FRC_SDCLK_ON
[    2.787536] sdhci-esdhc-imx 2194000.usdhc: change pinctrl state for uhs 0
[    2.787548] sdhci-esdhc-imx 2194000.usdhc: desired SD clock: 400000, actual: 386718
[    2.787554] mmc1: setting ESDHC_VENDOR_SPEC_FRC_SDCLK_ON
[    2.789560] mmc1: card failed to indicate switch to low voltage mode

This appears to correspond with the sequence:

CMD11 -> clock off -> set vselect -> clock on -> clock off ->
set pinctrl -> clock on -> test D[3:0]

which appears not to be the expected sequence - the expected sequence
should be:

CMD11 -> clock off -> set vselect -> clock on -> test D[3:0]

maybe with the setting of the IOMUX settings somewhere in there -
probably at the point where the clock is off - the additional clock
off/clock on step looks to me incorrect.

In any case, I've also augmented the other failure paths in
mmc_set_signal_voltage(), and it's always this one (the last step)
which fails:

        if (host->ops->card_busy && host->ops->card_busy(host)) {
                pr_debug("%s: card failed to indicate switch to low voltage mode\n",
                         mmc_hostname(host));
                err = -EAGAIN;
        }

Any ideas?

Thanks.

-- 
FTTC broadband for 0.8mile line: 5.8Mbps down 500kbps up.  Estimation
in database were 13.1 to 19Mbit for a good line, about 7.5+ for a bad.
Estimate before purchase was "up to 13.2Mbit".