[PATCH v2 0/1] AM65x MMC power-off delay fix

[PATCH v2 0/1] AM65x MMC power-off delay fix

[Judith Mendez]

This series adds power-off-delay-us in AM65x EVM DT to ensure proper MMC
card power cycling during boot.

AM65x EVM VDD rail discharges slowly (~632.97ms) through RC circuit.
Without sufficient power-off delay, SD card boot fails in bootloader stage.

AM65x SD boot failure was initially exposed by U-Boot MMC driver patch [0],
which was correct but revealed EVM hardware limitation. There is no SD card
boot failure in Linux yet, but proper power cycling is required regardless.
Additionally, equivalent Linux kernel discussions for similar fix [0] are
ongoing. Linux MMC driver now supports delay after MMC power-off [1] and
this patch adds power-off-delay-us=650ms to AM65x EVM DT.

Links:
[0] U-Boot patch & debug discussion:
https://lore.kernel.org/u-boot/d17a810c-e2db-4a24-a37d-2d7e02466ce9@ti.com/

[1] Merged power_off_delay_us support in Linux MMC:
https://lore.kernel.org/linux-mmc/20260806162202.657512-1-jm@ti.com/

V1: https://lore.kernel.org/linux-devicetree/20260908170635.238775-1-jm@ti.com/

Changes since v1:
- Fix commit subject and description
- Add cover letter to provide full context of implementation & history

Judith Mendez (1):
  arm64: dts: ti: k3-am654-base-board: Add power-off delay for proper
    MMC power cycle

 arch/arm64/boot/dts/ti/k3-am654-base-board.dts | 1 +
 1 file changed, 1 insertion(+)

-- 
2.34.1

[PATCH v2 1/1] arm64: dts: ti: k3-am654-base-board: Add power-off delay for proper MMC power cycle

[Judith Mendez]

The AM65x EVM MMC1 VDD rail discharges slowly through RC circuit.
SD spec (section 6.4.1.3) requires VDD < 0.5V for minimum 1ms during
power cycle. Measured discharge time on this board is ~632.97ms to
reach < 0.5V threshold.

During boot, MMC power cycles between boot stages. Without power off
delay, VDD doesn't fully discharge. Card retains 1.8V signaling state
from previous boot stages. When MMC driver later initializes, card no
longer asserts S18A in ACMD41 response (already switched to 1.8V). Host
misinterprets card state and forces 1.8V anyway, falling into a bad
state and causes MMC init failure with "unable to select a mode"
signature.

Add power-off-delay-us = 650000 (650ms) to ensure proper VDD discharge
during power cycles, allowing card to fully reset state between boot
stages.

Signed-off-by: Judith Mendez <jm@ti.com>
---
Changes since v1:
- Fixup commit header and description
---
 arch/arm64/boot/dts/ti/k3-am654-base-board.dts | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/boot/dts/ti/k3-am654-base-board.dts b/arch/arm64/boot/dts/ti/k3-am654-base-board.dts
index ca1300e130936..edcf039ccfbd0 100644
--- a/arch/arm64/boot/dts/ti/k3-am654-base-board.dts
+++ b/arch/arm64/boot/dts/ti/k3-am654-base-board.dts
@@ -460,6 +460,7 @@ &sdhci0 {
 &sdhci1 {
 	status = "okay";
 	vmmc-supply = <&vdd_mmc1_sd>;
+	power-off-delay-us = <650000>;
 	pinctrl-names = "default";
 	pinctrl-0 = <&main_mmc1_pins_default>;
 	ti,driver-strength-ohm = <50>;
-- 
2.34.1