linux-kernel - Re: [PATCH v2 4/5] arm64: dts: ti: k3-am62p5-sk: Enable Main UART wakeup

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Message-ID: <44b21f10-2ad4-4c88-a8e8-f485ecb53af9@ti.com>
Date: Mon, 5 Jan 2026 16:06:29 -0600
From: Kendall Willis <k-willis@...com>
To: Nishanth Menon <nm@...com>
CC: Vignesh Raghavendra <vigneshr@...com>, Tero Kristo <kristo@...nel.org>,
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, <d-gole@...com>, <vishalm@...com>,
	<sebin.francis@...com>, <msp@...libre.com>, <khilman@...libre.com>,
	<a-kaur@...com>, <s-kochidanadu@...com>,
	<linux-arm-kernel@...ts.infradead.org>, <devicetree@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 4/5] arm64: dts: ti: k3-am62p5-sk: Enable Main UART
 wakeup

On 1/5/26 07:52, Nishanth Menon wrote:
> On 20:38-20251230, Kendall Willis wrote:
>> The Main UART can resume from suspend to RAM states when PIN_WKUP_EN
>> is enabled. Add the necessary pins needed to wakeup the system. Add the
>> system idle states that the Main UART can wakeup the system from.
> 
> Is the tx and rx pin register states both lost? I wonder why during
> "wakeup" we set PIN_WKUP_EN ? is'nt that supposed to be set while
> entering "suspend" state?
> 

The UART driver uses the default pinctrl state when the system is 
active. During the process of suspend, the wakeup pinctrl state is 
selected by the UART driver in order to allow wakeup. Upon resume, the 
default pinctrl state is selected again.

> if the tx pin register state is not lost, then all we need to do is
> play with the rx pin state (and leave pinctrl-0 as is)?
> 

Yes, it can be done where the pinctrl-0 does not change, and there is an 
additional pinctrl pins that has the TX and RX with PIN_WKUP_EN. The 
logic behind both implementations are the same, just a different approach.

>>
>> Signed-off-by: Kendall Willis <k-willis@...com>
>> ---
>>   arch/arm64/boot/dts/ti/k3-am62p5-sk.dts | 24 ++++++++++++++++++++----
>>   1 file changed, 20 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/arm64/boot/dts/ti/k3-am62p5-sk.dts b/arch/arm64/boot/dts/ti/k3-am62p5-sk.dts
>> index ef719c6334fc094f01d9e8185992f2f58320e17d..96bba65f4f16792834567324db6f7f2bdee7bc06 100644
>> --- a/arch/arm64/boot/dts/ti/k3-am62p5-sk.dts
>> +++ b/arch/arm64/boot/dts/ti/k3-am62p5-sk.dts
>> @@ -328,14 +328,26 @@ AM62PX_IOPAD(0x0164, PIN_INPUT, 0) /* (A20) RGMII2_TX_CTL */
>>   		bootph-all;
>>   	};
>>   
>> -	main_uart0_pins_default: main-uart0-default-pins {
>> +	main_uart0_tx_pins_default: main-uart0-tx-default-pins {
>>   		pinctrl-single,pins = <
>> -			AM62PX_IOPAD(0x1c8, PIN_INPUT, 0)	/* (A22) UART0_RXD */
>>   			AM62PX_IOPAD(0x1cc, PIN_OUTPUT, 0)	/* (B22) UART0_TXD */
>>   		>;
>>   		bootph-all;
>>   	};
>>   
>> +	main_uart0_rx_pins_default: main-uart0-rx-default-pins {
>> +		pinctrl-single,pins = <
>> +			AM62PX_IOPAD(0x1c8, PIN_INPUT, 0)	/* (A22) UART0_RXD */
>> +		>;
>> +		bootph-all;
>> +	};
>> +
>> +	main_uart0_rx_pins_wakeup: main-uart0-rx-wakeup-pins {
>> +		pinctrl-single,pins = <
>> +			AM62PX_IOPAD(0x1c8, PIN_INPUT | PIN_WKUP_EN, 0)	/* (A22) UART0_RXD */
>> +		>;
>> +	};
>> +
>>   	main_uart1_pins_default: main-uart1-default-pins {
>>   		pinctrl-single,pins = <
>>   			AM62PX_IOPAD(0x0194, PIN_INPUT, 2) /* (D25) MCASP0_AXR3.UART1_CTSn */
>> @@ -692,8 +704,12 @@ partition@...0000 {
>>   };
>>   
>>   &main_uart0 {
>> -	pinctrl-names = "default";
>> -	pinctrl-0 = <&main_uart0_pins_default>;
>> +	pinctrl-names = "default", "wakeup";
>> +	pinctrl-0 = <&main_uart0_tx_pins_default>, <&main_uart0_rx_pins_default>;
>> +	pinctrl-1 = <&main_uart0_tx_pins_default>, <&main_uart0_rx_pins_wakeup>;
>> +	wakeup-source = <&system_deep_sleep>,
>> +			<&system_mcu_only>,
>> +			<&system_standby>;
>>   	status = "okay";
>>   	bootph-all;
>>   };
>>
>> -- 
>> 2.34.1
>>
> 

Best,
Kendall