(Resending to the list only; my first reply was rejected by the list server. Sorry for the duplicate.)
Hi Quentin, Thank you for the review. On 10/16/26, Quentin Schulz wrote: > I'll let Neil decide since he's the maintainer of that code, but I don't > think this is necessarily correct? The spec specifically allows > 2.7-3.6V, c.f. https://www.sdcard.org/developers/sd-standard-overview/. > > Moreover, RK3399 Puma has 1.8-3.0V only, and it's been working fine for > years now (though I haven't checked with that SD card specifically). > > What happens if you do NOT use the SD in U-Boot at all and boot straight > to the Linux kernel, is it also broken in the Linux kernel then? If not, > then your issue is probably not what your tool output and we may have an > issue elsewhere (possibly in the MMC subsystem for example). Linux is fine with this card at 3.0V. Linux itself sets vddio_c to 3.0V, and the system runs from the same card (SD high speed, 50MHz) with no errors in dmesg. Following your comments, I tested again without this patch, and I can no longer reproduce the problem. I tried U-Boot 2025.07, 2026.07 and 2026.10, with and without patch 1/2, and three SD cards, including the one in the commit message. In about 35 reboots from Linux, U-Boot always read the card and booted the kernel. At the U-Boot prompt after a reboot, vddio_c was 3.0V and the SD card ran at 40MHz, so the conditions were the same as in my original report. I do not know what was different when I saw the failure. So I agree that 3.0V is probably not the cause, and I will drop this patch. If I can reproduce the problem again, I will look at it again, including the MMC side as you suggested. Neil, sorry for the noise. Best regards, Shigeaki Asai (This reply was written with the help of Claude.)
