On Tue, 30 Jul 2019 at 15:17, Phil Elwell <phil@xxxxxxxxxxxxxxx> wrote: > > Hi MMC team, > > I've spent some time trying to add a regulator to control power to an SD card > (vmmc-supply) on an SDHCI-equipped system. After a few false starts and red herrings > I found that powering up the regulator during the boot process was effectively disabling > the SDHCI controller. Note that this was despite having regulator-boot-on set in the > device tree. > > The problem seems to be in sdhci_set_power_reg: > > mmc_regulator_set_ocr(mmc, mmc->supply.vmmc, vdd); > > if (mode != MMC_POWER_OFF) > sdhci_writeb(host, SDHCI_POWER_ON, SDHCI_POWER_CONTROL); > else > sdhci_writeb(host, 0, SDHCI_POWER_CONTROL); > > This looks plausible for the MMC_POWER_OFF case, but setting the SDHCI_POWER_CONTROL > register to SDHCI_POWER_ON (0x01) has the side effect of settings the SD Bus Voltage > Select bits to 0b000 (a reserved value). > > sdhci_set_power_noreg() includes logic to calculate the correct values for the voltage > select bits, so I found that (in my limited test cases) replacing the if/else above > with a chain call to sdhci_set_power_noreg() was sufficient to get everything working. > > Can anyone tell me what I've been doing wrong, or suggest a better "fix"? There are other sdhci variants having the similar needs, hence we have the flexibility available via using the optional ->set_power() callback. Have a look at sdhci_arasan_set_power(), for example. Kind regards Uffe
