On 6/3/24 22:28, Tim Harvey wrote: > On Mon, Jun 3, 2024 at 1:18 AM Christian Loehle > <christian.loehle@xxxxxxx> wrote: >> >> On 5/31/24 21:47, Tim Harvey wrote: >>> Greetings, >>> >>> I'm seeing an issue on an imx8mm board (imx8mm-venice-gw73xx) where >>> for a specific set of microsd cards if I have accessed the microsd in >>> U-Boot with UHS/1.8V the kernel will not recognize that microsd when >>> scanning. >>> >>> The issue does not occur with all microsd cards but seems to appear >>> with a large sample size of a specific card/model (Kingston SDC32 32GB >>> SDR104 card). I do not see a signal integrity issue on the scope. >>> >>> Instrumenting the kernel the issue is that the host reports a CRC >>> error as soon as the first mmc_send_if_cond call which occurs in >>> mmc_rescan_try_freq. >>> >>> I can avoid the issue by either not accessing the microsd in U-Boot or >>> by disabling UHS/1.8V mode in U-Boot therefore what I think is >>> happening is that U-Boot leaves the card in UHS/1.8V signalling mode >>> and when the kernel scans it sets the voltage back to 3.3V >>> standard/default and default timings then issues its clock cycles to >>> 'reset' the card and the card does not recognize the reset. I'm >>> wondering if this is because the reset is done via clock cycles after >>> the kernel has set the I/O voltage back to 3.3V when perhaps the card >>> is still in 1.8V mode (although I don't see how that would cause an >>> issue)? >> >> It will cause an issue for many cards and might break some cards. >> >>> >>> Is there some sort of MMC 'reset' I can/should do in U-Boot before >>> booting the kernel? Has anyone encountered anything like this before? >> >> There is no 'switching back' to 3.3V signalling from UHS 1.8V. >> The only way this can be done is therefore a full power-off. >> Is that done correctly for your system? >> AFAIR spec dictates 500ms of <0.5V on VCC. Note that driving CLK/signal >> lines can also sustain the card somewhat, as leakage is only limited >> within operating voltage. > > Hi Christian, > > Are you saying the only way to properly reset from 1.8V is to have a > VDD supply on the microSD card that can be turned off before booting > to Linux? We have never had that before and never encountered > something like this. Yes, the only safe way to use UHS-I really anyway. You could disable UHS for u-boot but that still leaves (potentially) problematic warm-reboots of the board. Having a (software-controlled) switchable regulator on SD VCC is pretty common for this reason and you should be able to find it in most dts for host controllers with sd-uhs-* property. I'm afraid that the relevant spec section isn't available in the simplified version. Kind Regards, Christian
