Re: [PATCH 1/2] arm64: dts: amlogic: t7: use the real UART pclk
From: Lucas Tanure
Date: Mon Aug 24 2026 - 05:34:27 EST
On 24/08/2026 10:15, Ronald Claveau wrote:
On 8/23/26 1:39 PM, Lucas Tanure wrote:Hi Ronald,
On 19/08/2026 08:25, Ronald Claveau wrote:
On 8/19/26 4:39 AM, Xianwei Zhao wrote:Thanks for pointing out that series, though I wasn't aware of it.
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@xxxxxxxxx>
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?
It seems similar to changes in this series :
https://lore.kernel.org/all/20260420-add-bluetooth-t7-vim4-
v4-0-9505df0e7016@xxxxxxxx/
What do you think ?
And after reading I don't agree with it. The clocks are not redundant,
they are there because we agreed sometime ago that xtal belongs to the
board files.
So I still vote for my change in v2, that I will send in a few minutes.
I don't get why it would be better to define the exact same clocks in
each DTS file.
The xtal recommended characteristics provided at the SOC level can be
defined in the DTSI and overridden, if really necessary, in the DTS.
The preference for keeping xtal in board-specific .dts files rather than the SoC .dtsi comes down to DT hardware modeling principles and upstream maintainer guidelines:
Hardware Topology: The xtal is physically located on the board PCB, not inside the SoC silicon. The .dtsi file models the SoC silicon internal architecture (clock controllers, IPs, registers), whereas .dts files describe the physical board layout surrounding it.
Avoiding Implicit Assumptions: Defining a default 24MHz xtal in .dtsi assumes every T7 board will use the same oscillator configuration. If a custom board design uses a different crystal frequency or an external clock generator/TCXO, overriding a .dtsi-level node can lead to messy DT overrides or silent clock rate mismatches if forgotten.
Upstream DT Maintainer Policy: Kernel DT maintainers consistently push to keep board-level hardware explicitly declared in the board .dts files to reflect actual physical board components.
That said, I acknowledge the trade-off is minor boilerplate duplication across board DTS files. If the Amlogic SoC maintainers prefer setting a default 24MHz xtal in amlogic-t7.dtsi to match older SoC generations, I am open to updating it—provided the maintainers explicitly prefer that tradeoff over strict DT topology modeling.
Best regards,
Lucas