Re: [PATCH 1/2] arm64: dts: amlogic: t7: use the real UART pclk
From: Neil Armstrong
Date: Thu Aug 27 2026 - 04:47:36 EST
On 8/25/26 10:54, Ronald Claveau wrote:
On 8/24/26 11:32 AM, Lucas Tanure wrote:
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.
Hi Lucas,
Thank you for this detailed explanation.
I was referring to the last paragraph of the DTS coding style:
Hardware components that are present on the board shall be placed in the
board DTS, not in the SoC or SoM DTSI. A partial exception is a common
external reference SoC input clock, which could be coded as a
fixed-clock in the SoC DTSI with its frequency provided by each board DTS.
This is what was done for qualcomm SoCs, we could do it for Amlogic aswell.
I understand going to strict topology is better, that means we must
apply the same rules to new Amlogic SOCs, right ?
Do we need to move other clocks and assigned-clocks properties which use
the xtal to the board DTS as well (such as clkc_periphs or sd_emmc)?
No since it describes a SoC configuration using XTAL, it should be in the dtsi.
Neil