+ Adrian On Fri, 2 Aug 2019 at 15:23, Phil Elwell <phil@xxxxxxxxxxxxxxx> wrote: > > 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? Good question, but unfortunate I don't know the SDHCI spec in that great detail. And in the end, it has turned out that variants seems to differs in regards to this register. I looped in Adrian, to see if he has some comments. Kind regards Uffe
