On Tue Jun 4, 2024 at 9:47 AM CEST, Christian Loehle wrote: > On 6/3/24 22:28, Tim Harvey wrote: > > On Mon, Jun 3, 2024 at 1:18 AM Christian Loehle > > <christian.loe...@arm.com> 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.
I can second that. And also keep in mind that the actual supply voltage must be below that threshold. Thus, the power-off time also depends on the capacitance on that supply line after the power load switch. There are switches with dedicated output discharge circuits built-in. That being said, from my experience there are cards which will work when switching back from 1V8 to 3V3 signalling and some don't. I haven't digged deeper into that topic, though. -michael > 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
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