[PATCH 0/2] arm64: dts: amlogic: t7: fix UART clock and SD card recovery

[PATCH 0/2] arm64: dts: amlogic: t7: fix UART clock and SD card recovery

[Lucas Tanure]

Two fixes found while booting mainline on a Khadas VIM4.

The first one wires uart_a to the real UART bus clock. It was pointed at
the 24MHz crystal as a placeholder, because the T7 clock controller
driver did not exist when these boards were added. That leaves the real
clock without a user, so the kernel turns it off when it disables unused
clocks at the end of boot, and the board hangs with the console gone.

The second one drops regulator-always-on from the SD card supply. A card
that refuses the 1.8V UHS switch can only be recovered by removing its
power, which that property prevents, so the card never initialises and
the MMC core retries forever.

Both were tested on a Khadas VIM4 booting v7.2 from the SD card.

Lucas Tanure (2):
  arm64: dts: amlogic: t7: use the real UART pclk
  arm64: dts: amlogic: t7: khadas-vim4: allow the SD card to be power
    cycled

 arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-an400.dts       | 2 --
 arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-khadas-vim4.dts | 3 ---
 arch/arm64/boot/dts/amlogic/amlogic-t7.dtsi                   | 4 ++++
 3 files changed, 4 insertions(+), 5 deletions(-)

--
2.55.0

[PATCH 1/2] arm64: dts: amlogic: t7: use the real UART pclk

[Lucas Tanure]

uart_a lists the 24MHz crystal for all three of its clocks, because
the T7 clock controller driver did not exist when these boards were
added.

That leaves the real UART bus clock without a user, so the kernel
turns it off when it disables unused clocks at the end of boot, and
the board hangs.

Point uart_a at the real clocks, the way meson-s4.dtsi does, and drop
the placeholders from the two board files.

Fixes: 4fef056588f5 ("arm64: dts: amlogic-t7-a311d2-khadas-vim4: add initial device-tree")
Fixes: 6f048cc7a635 ("arm64: dts: add board AN400")
Signed-off-by: Lucas Tanure <tanure@linux.com>
Assisted-by: Claude:claude-fable-5
---
 arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-an400.dts       | 2 --
 arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-khadas-vim4.dts | 2 --
 arch/arm64/boot/dts/amlogic/amlogic-t7.dtsi                   | 4 ++++
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-an400.dts b/arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-an400.dts
index cab2ee9ea0d3..dcbcd08a78b9 100644
--- a/arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-an400.dts
+++ b/arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-an400.dts
@@ -33,7 +33,5 @@ xtal: xtal-clk {
 };
 
 &uart_a {
-	clocks = <&xtal>, <&xtal>, <&xtal>;
-	clock-names = "xtal", "pclk", "baud";
 	status = "okay";
 };
diff --git a/arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-khadas-vim4.dts b/arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-khadas-vim4.dts
index c41525a34b72..677069e58f30 100644
--- a/arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-khadas-vim4.dts
+++ b/arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-khadas-vim4.dts
@@ -266,6 +266,4 @@ &sd_emmc_c {
 
 &uart_a {
 	status = "okay";
-	clocks = <&xtal>, <&xtal>, <&xtal>;
-	clock-names = "xtal", "pclk", "baud";
 };
diff --git a/arch/arm64/boot/dts/amlogic/amlogic-t7.dtsi b/arch/arm64/boot/dts/amlogic/amlogic-t7.dtsi
index cc371fcd1896..7847582e77ed 100644
--- a/arch/arm64/boot/dts/amlogic/amlogic-t7.dtsi
+++ b/arch/arm64/boot/dts/amlogic/amlogic-t7.dtsi
@@ -587,6 +587,10 @@ uart_a: serial@78000 {
 				compatible = "amlogic,t7-uart", "amlogic,meson-s4-uart";
 				reg = <0x0 0x78000 0x0 0x18>;
 				interrupts = <GIC_SPI 168 IRQ_TYPE_EDGE_RISING>;
+				clocks = <&xtal>,
+					 <&clkc_periphs CLKID_SYS_UART_A>,
+					 <&xtal>;
+				clock-names = "xtal", "pclk", "baud";
 				status = "disabled";
 			};
 
-- 
2.55.0

Re: [PATCH 1/2] arm64: dts: amlogic: t7: use the real UART pclk

[Xianwei Zhao]

Hi Lucas,

On 2026/8/19 03:11, Lucas Tanure wrote:
> uart_a lists the 24MHz crystal for all three of its clocks, because
> the T7 clock controller driver did not exist when these boards were
> added.
> 
> That leaves the real UART bus clock without a user, so the kernel
> turns it off when it disables unused clocks at the end of boot, and
> the board hangs.
> 
> Point uart_a at the real clocks, the way meson-s4.dtsi does, and drop
> the placeholders from the two board files.
> 
> Fixes: 4fef056588f5 ("arm64: dts: amlogic-t7-a311d2-khadas-vim4: add initial device-tree")
> Fixes: 6f048cc7a635 ("arm64: dts: add board AN400")
> Signed-off-by: Lucas Tanure<tanure@linux.com>
> Assisted-by: Claude:claude-fable-5
> ---
>   arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-an400.dts       | 2 --
>   arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-khadas-vim4.dts | 2 --
>   arch/arm64/boot/dts/amlogic/amlogic-t7.dtsi                   | 4 ++++
>   3 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-an400.dts
> b/arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-an400.dts
> index cab2ee9ea0d3..dcbcd08a78b9 100644
> --- a/arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-an400.dts
> +++ b/arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-an400.dts
> @@ -33,7 +33,5 @@ xtal: xtal-clk {
>   };
> 
>   &uart_a {
> -       clocks = <&xtal>, <&xtal>,
> <&xtal>;
> -       clock-names = "xtal", "pclk", "baud";
>          status = "okay";
>   };
> diff --git
> a/arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-khadas-vim4.dts
> b/arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-khadas-vim4.dts
> index c41525a34b72..677069e58f30 100644
> --- a/arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-khadas-vim4.dts
> +++ b/arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-khadas-vim4.dts
> @@ -266,6 +266,4 @@ &sd_emmc_c {
> 
>   &uart_a {
>          status = "okay";
> -       clocks = <&xtal>, <&xtal>,
> <&xtal>;
> -       clock-names = "xtal", "pclk", "baud";
>   };
> diff --git a/arch/arm64/boot/dts/amlogic/amlogic-t7.dtsi
> b/arch/arm64/boot/dts/amlogic/amlogic-t7.dtsi
> index cc371fcd1896..7847582e77ed 100644
> --- a/arch/arm64/boot/dts/amlogic/amlogic-t7.dtsi
> +++ b/arch/arm64/boot/dts/amlogic/amlogic-t7.dtsi
> @@ -587,6 +587,10 @@ uart_a: serial@78000 {
>                                  compatible = "amlogic,t7-uart",
> "amlogic,meson-s4-uart";
>                                  reg = <0x0 0x78000 0x0 0x18>;
>                                  interrupts = <GIC_SPI 168
> IRQ_TYPE_EDGE_RISING>;
> +                               clocks = <&xtal>,
> +                                        <&clkc_periphs
> CLKID_SYS_UART_A>,
> +                                        <&xtal>;
> +                               clock-names = "xtal", "pclk", "baud";
>                                  status = "disabled";
>                          };

I agree with moving the UART clock configuration to the DTSI file. 
However, it seems a little odd to keep the XTAL clock definition in the 
DTS, as the alias may not be consistent across different boards, which 
could result in compilation errors. Could we move the XTAL clock 
definition to the DTSI as well, similar to other Amlogic SoCs?

[PATCH 2/2] arm64: dts: amlogic: t7: khadas-vim4: allow the SD card to be power cycled

[Lucas Tanure]

SD cards start at 3.3V and switch to 1.8V to reach UHS-I speeds. Some
cards refuse that switch, and the SD specification says the only way
to recover is to power the card off and start again.

SD_3V3 is marked regulator-always-on, so the supply never goes off,
the card stays stuck half way through the switch, and the MMC core
retries forever:

  mmc1: error -95 whilst initialising SD card

Drop regulator-always-on. regulator-boot-on still turns the supply on
at boot, and a card that refuses the switch now falls back to high
speed instead of failing to initialise.

Fixes: 8c45bf9ae4ef ("arm64: dts: amlogic: t7: khadas-vim4: Add power regulators")
Signed-off-by: Lucas Tanure <tanure@linux.com>
Assisted-by: Claude:claude-fable-5
---
 arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-khadas-vim4.dts | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-khadas-vim4.dts b/arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-khadas-vim4.dts
index 677069e58f30..3f53630e107f 100644
--- a/arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-khadas-vim4.dts
+++ b/arch/arm64/boot/dts/amlogic/amlogic-t7-a311d2-khadas-vim4.dts
@@ -71,7 +71,6 @@ sd_3v3: regulator-sdcard-3v3 {
 		vin-supply = <&vddao_3v3>;
 		gpio = <&gpio GPIOD_11 GPIO_ACTIVE_LOW>;
 		regulator-boot-on;
-		regulator-always-on;
 	};
 
 	sdio_pwrseq: sdio-pwrseq {
-- 
2.55.0