From: Valerio Setti <vsetti@baylibre.com>

This is meant to resolve reboot not working on this board.

The problem is as follows. In order to be able to switch from HS to UHS
mode the bus voltage needs to be reduced from 3.3V down to 1.8V and this
is achieved by the "vqmmc-supply" regulator. The ROM bootloader is only
able to manage the card in HS mode (3.3V) and the switch HS->UHS happen
at boottime in the kernel. The problem appears when the reboot command
is issued or watchdog expires because in this case the "vqmmc-supply"
voltage is not returned back at 3.3V before rebooting the board so the
ROM bootloader will be completely stuck.

Therefore this commit removes all UHS modes which would cause
"vqmmc-summply" to switch from 3.3V to 1.8V.

In terms of performance the main drawback of this commit is limiting the
SD card bus speed to HS (25 MB/s) instead of UHS DDR50 (50 MB/s). However
this comes with the benefit of being able to reboot the board, so it
sounds like a reasonable compromise.

Reviewed-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Valerio Setti <vsetti@baylibre.com>
---
Changes in v2:
- Re-added vqmmc-supply to sd_emmc_b node.
- Link to v1: https://lore.kernel.org/r/20250907-fix-reboot-v1-1-7606fc91254e@baylibre.com
---
 arch/arm64/boot/dts/amlogic/meson-gxbb-odroidc2.dts | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/arch/arm64/boot/dts/amlogic/meson-gxbb-odroidc2.dts b/arch/arm64/boot/dts/amlogic/meson-gxbb-odroidc2.dts
index 959bd8d77a82ebc78c5e0592d7613e692e4ede4e..12e26f99d4f080a216e305981dc4291a49063b60 100644
--- a/arch/arm64/boot/dts/amlogic/meson-gxbb-odroidc2.dts
+++ b/arch/arm64/boot/dts/amlogic/meson-gxbb-odroidc2.dts
@@ -348,10 +348,6 @@ &sd_emmc_b {
 
 	bus-width = <4>;
 	cap-sd-highspeed;
-	sd-uhs-sdr12;
-	sd-uhs-sdr25;
-	sd-uhs-sdr50;
-	sd-uhs-ddr50;
 	max-frequency = <100000000>;
 	disable-wp;
 

---
base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585
change-id: 20250907-fix-reboot-04e0fc919ae0

Best regards,
-- 
Valerio Setti <vsetti@baylibre.com>

Hi,

On Mon, 08 Sep 2025 21:50:03 +0200, Valerio Setti wrote:
> This is meant to resolve reboot not working on this board.
> 
> The problem is as follows. In order to be able to switch from HS to UHS
> mode the bus voltage needs to be reduced from 3.3V down to 1.8V and this
> is achieved by the "vqmmc-supply" regulator. The ROM bootloader is only
> able to manage the card in HS mode (3.3V) and the switch HS->UHS happen
> at boottime in the kernel. The problem appears when the reboot command
> is issued or watchdog expires because in this case the "vqmmc-supply"
> voltage is not returned back at 3.3V before rebooting the board so the
> ROM bootloader will be completely stuck.
> 
> [...]

Thanks, Applied to https://git.kernel.org/pub/scm/linux/kernel/git/amlogic/linux.git (v6.18/arm64-dt)

[1/1] arm64: dts: amlogic: gxbb-odroidc2: remove UHS capability for SD card
      https://git.kernel.org/amlogic/c/663bfe77b6f70bcb33b2607e16c94fcb1029580e

These changes has been applied on the intermediate git tree [1].

The v6.18/arm64-dt branch will then be sent via a formal Pull Request to the Linux SoC maintainers
for inclusion in their intermediate git branches in order to be sent to Linus during
the next merge window, or sooner if it's a set of fixes.

In the cases of fixes, those will be merged in the current release candidate
kernel and as soon they appear on the Linux master branch they will be
backported to the previous Stable and Long-Stable kernels [2].

The intermediate git branches are merged daily in the linux-next tree [3],
people are encouraged testing these pre-release kernels and report issues on the
relevant mailing-lists.

If problems are discovered on those changes, please submit a signed-off-by revert
patch followed by a corrective changeset.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/amlogic/linux.git
[2] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
[3] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git

-- 
Neil