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Thu, 8 Jan 2026 11:52:32 -0600 Received: from [128.247.81.19] (uda0506412.dhcp.ti.com [128.247.81.19]) by lelvem-mr06.itg.ti.com (8.18.1/8.18.1) with ESMTP id 608HqWWe2762413; Thu, 8 Jan 2026 11:52:32 -0600 Message-ID: Date: Thu, 8 Jan 2026 11:52:32 -0600 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/3] arm64: boot: dts: ti: k3-am62l: allow WKUP UART wakeup from LPM To: Bryan Brattlof CC: Nishanth Menon , Vignesh Raghavendra , "Tero Kristo" , Rob Herring , "Krzysztof Kozlowski" , Conor Dooley , "Dhruva Gole" , , , , , , , , , References: <20260106-wkup-uart-wakeup-v2-0-fb4cbd56c827@ti.com> <20260107164504.ehvbfizg7ybbvv2e@bryanbrattlof.com> <20260108170545.cfez6dvwkft2z3jh@bryanbrattlof.com> Content-Language: en-US From: Kendall Willis In-Reply-To: <20260108170545.cfez6dvwkft2z3jh@bryanbrattlof.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-C2ProcessedOrg: 333ef613-75bf-4e12-a4b1-8e3623f5dcea X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH2PEPF0000009E:EE_|DM4PR10MB7390:EE_ X-MS-Office365-Filtering-Correlation-Id: 61b533d5-7411-4f55-f587-08de4edeb39b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|82310400026|1800799024|36860700013|34020700016|34070700014; 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X-OriginatorOrg: ti.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Jan 2026 17:52:33.5264 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 61b533d5-7411-4f55-f587-08de4edeb39b X-MS-Exchange-CrossTenant-Id: e5b49634-450b-4709-8abb-1e2b19b982b7 X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=e5b49634-450b-4709-8abb-1e2b19b982b7;Ip=[198.47.23.194];Helo=[lewvzet200.ext.ti.com] X-MS-Exchange-CrossTenant-AuthSource: CH2PEPF0000009E.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM4PR10MB7390 On 1/8/26 11:05, Bryan Brattlof wrote: > On January 7, 2026 thus sayeth Kendall Willis: >> On 1/7/26 10:45, Bryan Brattlof wrote: >>> On January 6, 2026 thus sayeth Kendall Willis: >>>> K3 TI AM62L SoC supports wakeup from WKUP UART when the SoC is in the >>>> DeepSleep low power mode. To allow wakeup from WKUP UART the target-module >>>> device tree node is enabled. The ti-sysc interconnect target module driver >>>> is used to configure the the SYSCONFIG related registers. In this case, >>>> the interconnect target module node configures the WKUP UART to be able to >>>> wakeup from system suspend. The SYSC register is used to enable wakeup >>>> from system suspend for the WKUP UART. Refer to 14.7.2.5 UART in the >>>> AM62L Techincal Reference Manual for registers referenced [1]. >>>> >>>> Previous TI SoCs configure the WKUP UART to wakeup from system suspend >>>> using the ti-sysc interconnect target module driver. Refer to commit >>>> ce27f7f9e328 ("arm64: dts: ti: k3-am62-wakeup: Configure ti-sysc for >>>> wkup_uart0") for an example of this. >>> >>> I think I may be confused. What is setting the pinmux for the wkup_uart >>> to allow us to trigger the wake event? It looks like they reset to GPIO >>> pins if not set. Is firmware doing this? >> >> On AM62L, the WKUP UART pinmux is initially set by TFA so that it is set to >> the UART pins, not GPIO. The target-module node sets the WKUP UART SYSC >> register so that wakeup is enabled. >> > > Nice however should we mark the UART in the board file as reserved for > TFA or is it free to be used by Linux and only during the low power > modes after Linux is asleep will it be used by TFA? > > ~Bryan Sorry for the confusion, I said earlier that the WKUP UART could be used by firmware, but that is not to say it is specifically reserved by the firmware in general. TFA sets the WKUP UART pins, but it does not use the WKUP UART for anything else. The only exception for TFA using the WKUP UART is if the user chooses to use the WKUP UART for TFA debugging [1]. All of this to say that the WKUP UART *can* be used by Linux, it does not need to be reserved for firmware. [1] https://software-dl.ti.com/processor-sdk-linux/esd/AM62LX/latest/exports/docs/linux/Foundational_Components/Power_Management/pm_am62lx_debug.html Best, Kendall