On Wed, 22 Apr 2020 at 15:40, Ludovic BARRE <ludovic.barre@xxxxxx> wrote: > > hi Ulf > > Le 4/21/20 à 11:38 AM, Ulf Hansson a écrit : > > On Tue, 21 Apr 2020 at 11:25, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote: > >> > >> On Mon, 20 Apr 2020 at 18:18, Ludovic Barre <ludovic.barre@xxxxxx> wrote: > >>> > >>> This patch fix a power-on issue, and avoid to retry the power sequence. > >>> > >>> In power off sequence: sdmmc must set pwr_reg in "power-cycle" state > >>> (value 0x2), to prevent the card from being supplied through the signal > >>> lines (all the lines are driven low). > >>> > >>> In power on sequence: when the power is stable, sdmmc must set pwr_reg > >>> in "power-off" state (value 0x0) to drive all signal to high before to > >>> set "power-on". > >> > >> Just a question to gain further understanding. > >> > >> Let's assume that the controller is a power-on state, because it's > >> been initialized by the boot loader. When the mmc core then starts the > >> power-on sequence (not doing a power-off first), would $subject patch > >> then cause the > >> MMCIPOWER to remain as is, or is it going to be overwritten? > > On sdmmc controller, the PWRCTRL[1:0] field of MMCIPOWER register allow > to manage sd lines and has a specific bahavior. > > PWRCTRL value: > - 0x0: After reset, Reset: the SDMMC is disabled and the clock to the > Card is stopped, SDMMC_D[7:0], and SDMMC_CMD are HiZ and > SDMMC_CK is driven low. > When written 00, power-off: the SDMMC is disabled and the clock > to the card is stopped, SDMMC_D[7:0], SDMMC_CMD and SDMMC_CK > are driven high. > > - 0x2: Power-cycle, the SDMMC is disabled and the clock to the card is > stopped, SDMMC_D[7:0], SDMMC_CMD and SDMMC_CK are driven low. > > - 0x3: Power-on: the card is clocked, The first 74 SDMMC_CK cycles the > SDMMC is still disabled. After the 74 cycles the SDMMC is > enabled and the SDMMC_D[7:0], SDMMC_CMD and SDMMC_CK are > controlled according the SDMMC operation. > **Any further write will be ignored, PWRCTRL value > will keep 0x3**. when the SDMMC is ON (0x3) only a reset could > change pwrctrl value and the state of sdmmc lines. > > So if the lines are already "ON", the power-on sequence (decribed in > commit message) not overwrite the pwctrl field and not disturb the sdmmc > lines. Thanks for the detailed information, much appreciated! > > >> > >> I am a little worried that we may start to rely on boot loader > >> conditions, which isn't really what we want either... > >> > > We not depend of boot loader conditions. > > This patch simply allows to drive high the sd lines before to set > "power-on" value (no effect if already power ON). Yep, thanks! > > >>> > >>> To avoid writing the same value to the power register several times, this > >>> register is cached by the pwr_reg variable. At probe pwr_reg is initialized > >>> to 0 by kzalloc of mmc_alloc_host. > >>> > >>> Like pwr_reg value is 0 at probing, the power on sequence fail because > >>> the "power-off" state is not writes (value 0x0) and the lines > >>> remain drive to low. > >>> > >>> This patch initializes "pwr_reg" variable with power register value. > >>> This it done in sdmmc variant init to not disturb default mmci behavior. > >>> > >>> Signed-off-by: Ludovic Barre <ludovic.barre@xxxxxx> > >> > >> Besides the comment, the code and the approach seems reasonable to me. > > > > Another related question. I just realized why you probably haven't set > > .pwrreg_nopower for the variant_stm32_sdmmc and variant_stm32_sdmmcv2. > > > > I guess it's because you need a slightly different way to restore the > > context of MMCIPOWER register at ->runtime_resume(), rather than just > > re-writing it with the saved register values. Is this something that > > you are looking into as well? > > Yes exactly, the sequence is slightly different. I can't write 0 on > mmci_runtime_suspend, and can't just re-writing the saved register. So, it seems like you need to use the ->set_ios() callback, to re-configure the controller correctly. Just tell if you need more help to make that work, otherwise I am here to review your patches. In regards to $subject patch, I have applied it for next, thanks! Kind regards Uffe
