Hi Uffe, On 02/08/2019 14:15, Ulf Hansson wrote: > 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. I don't understand. Can you explain what writing 0x0001 to the SDHCI_POWER_CONTROL register is supposed to do according to the specification? And why is the Arasan SDHCI implementation not the default? Thanks, Phil
