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([2600:1700:e321:62f0:da43:aeff:fecc:bfd5]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-134cc33aac9sm11334943c88.14.2026.05.16.11.33.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 16 May 2026 11:33:06 -0700 (PDT) Sender: Guenter Roeck Message-ID: <3dfcec0e-3ce9-440b-9377-deba8fa9f2eb@roeck-us.net> Date: Sat, 16 May 2026 11:33:05 -0700 Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/3] watchdog: realtek-otto: Change to use regmap API To: Sander Vanheule , Rustam Adilov , sashiko@lists.linux.dev Cc: linux-watchdog@vger.kernel.org, conor+dt@kernel.org, devicetree@vger.kernel.org, robh@kernel.org, krzk+dt@kernel.org, Wim Van Sebroeck References: <20260509163101.722793-2-adilov@disroot.org> <20260509171602.6B74FC2BCB2@smtp.kernel.org> <1d8a4fa99fa1af9e41f255ec147a7571@disroot.org> <173f0f7d804d3b0f33b6584b8a592d2079c593e9.camel@svanheule.net> Content-Language: en-US From: Guenter Roeck Autocrypt: addr=linux@roeck-us.net; keydata= xsFNBE6H1WcBEACu6jIcw5kZ5dGeJ7E7B2uweQR/4FGxH10/H1O1+ApmcQ9i87XdZQiB9cpN RYHA7RCEK2dh6dDccykQk3bC90xXMPg+O3R+C/SkwcnUak1UZaeK/SwQbq/t0tkMzYDRxfJ7 nyFiKxUehbNF3r9qlJgPqONwX5vJy4/GvDHdddSCxV41P/ejsZ8PykxyJs98UWhF54tGRWFl 7i1xvaDB9lN5WTLRKSO7wICuLiSz5WZHXMkyF4d+/O5ll7yz/o/JxK5vO/sduYDIlFTvBZDh gzaEtNf5tQjsjG4io8E0Yq0ViobLkS2RTNZT8ICq/Jmvl0SpbHRvYwa2DhNsK0YjHFQBB0FX IdhdUEzNefcNcYvqigJpdICoP2e4yJSyflHFO4dr0OrdnGLe1Zi/8Xo/2+M1dSSEt196rXaC kwu2KgIgmkRBb3cp2vIBBIIowU8W3qC1+w+RdMUrZxKGWJ3juwcgveJlzMpMZNyM1jobSXZ0 VHGMNJ3MwXlrEFPXaYJgibcg6brM6wGfX/LBvc/haWw4yO24lT5eitm4UBdIy9pKkKmHHh7s jfZJkB5fWKVdoCv/omy6UyH6ykLOPFugl+hVL2Prf8xrXuZe1CMS7ID9Lc8FaL1ROIN/W8Vk BIsJMaWOhks//7d92Uf3EArDlDShwR2+D+AMon8NULuLBHiEUQARAQABzTJHdWVudGVyIFJv ZWNrIChMaW51eCBhY2NvdW50KSA8bGludXhAcm9lY2stdXMubmV0PsLBgQQTAQIAKwIbAwYL CQgHAwIGFQgCCQoLBBYCAwECHgECF4ACGQEFAmgrMyQFCSbODQkACgkQyx8mb86fmYGcWRAA oRwrk7V8fULqnGGpBIjp7pvR187Yzx+lhMGUHuM5H56TFEqeVwCMLWB2x1YRolYbY4MEFlQg VUFcfeW0OknSr1s6wtrtQm0gdkolM8OcCL9ptTHOg1mmXa4YpW8QJiL0AVtbpE9BroeWGl9v 2TGILPm9mVp+GmMQgkNeCS7Jonq5f5pDUGumAMguWzMFEg+Imt9wr2YA7aGen7KPSqJeQPpj onPKhu7O/KJKkuC50ylxizHzmGx+IUSmOZxN950pZUFvVZH9CwhAAl+NYUtcF5ry/uSYG2U7 DCvpzqOryJRemKN63qt1bjF6cltsXwxjKOw6CvdjJYA3n6xCWLuJ6yk6CAy1Ukh545NhgBAs rGGVkl6TUBi0ixL3EF3RWLa9IMDcHN32r7OBhw6vbul8HqyTFZWY2ksTvlTl+qG3zV6AJuzT WdXmbcKN+TdhO5XlxVlbZoCm7ViBj1+PvIFQZCnLAhqSd/DJlhaq8fFXx1dCUPgQDcD+wo65 qulV/NijfU8bzFfEPgYP/3LP+BSAyFs33y/mdP8kbMxSCjnLEhimQMrSSo/To1Gxp5C97fw5 3m1CaMILGKCmfI1B8iA8zd8ib7t1Rg0qCwcAnvsM36SkrID32GfFbv873bNskJCHAISK3Xkz qo7IYZmjk/IJGbsiGzxUhvicwkgKE9r7a1rOwU0ETofVZwEQALlLbQeBDTDbwQYrj0gbx3bq 7kpKABxN2MqeuqGr02DpS9883d/t7ontxasXoEz2GTioevvRmllJlPQERVxM8gQoNg22twF7 pB/zsrIjxkE9heE4wYfN1AyzT+AxgYN6f8hVQ7Nrc9XgZZe+8IkuW/Nf64KzNJXnSH4u6nJM J2+Dt274YoFcXR1nG76Q259mKwzbCukKbd6piL+VsT/qBrLhZe9Ivbjq5WMdkQKnP7gYKCAi pNVJC4enWfivZsYupMd9qn7Uv/oCZDYoBTdMSBUblaLMwlcjnPpOYK5rfHvC4opxl+P/Vzyz 6WC2TLkPtKvYvXmdsI6rnEI4Uucg0Au/Ulg7aqqKhzGPIbVaL+U0Wk82nz6hz+WP2ggTrY1w ZlPlRt8WM9w6WfLf2j+PuGklj37m+KvaOEfLsF1v464dSpy1tQVHhhp8LFTxh/6RWkRIR2uF I4v3Xu/k5D0LhaZHpQ4C+xKsQxpTGuYh2tnRaRL14YMW1dlI3HfeB2gj7Yc8XdHh9vkpPyuT nY/ZsFbnvBtiw7GchKKri2gDhRb2QNNDyBnQn5mRFw7CyuFclAksOdV/sdpQnYlYcRQWOUGY HhQ5eqTRZjm9z+qQe/T0HQpmiPTqQcIaG/edgKVTUjITfA7AJMKLQHgp04Vylb+G6jocnQQX JqvvP09whbqrABEBAAHCwWUEGAECAA8CGwwFAmgrMyQFCSbODQkACgkQyx8mb86fmYHlgg/9 H5JeDmB4jsreE9Bn621wZk7NMzxy9STxiVKSh8Mq4pb+IDu1RU2iLyetCY1TiJlcxnE362kj njrfAdqyPteHM+LU59NtEbGwrfcXdQoh4XdMuPA5ADetPLma3YiRa3VsVkLwpnR7ilgwQw6u dycEaOxQ7LUXCs0JaGVVP25Z2hMkHBwx6BlW6EZLNgzGI2rswSZ7SKcsBd1IRHVf0miwIFYy j/UEfAFNW+tbtKPNn3xZTLs3quQN7GdYLh+J0XxITpBZaFOpwEKV+VS36pSLnNl0T5wm0E/y scPJ0OVY7ly5Vm1nnoH4licaU5Y1nSkFR/j2douI5P7Cj687WuNMC6CcFd6j72kRfxklOqXw zvy+2NEcXyziiLXp84130yxAKXfluax9sZhhrhKT6VrD45S6N3HxJpXQ/RY/EX35neH2/F7B RgSloce2+zWfpELyS1qRkCUTt1tlGV2p+y2BPfXzrHn2vxvbhEn1QpQ6t+85FKN8YEhJEygJ F0WaMvQMNrk9UAUziVcUkLU52NS9SXqpVg8vgrO0JKx97IXFPcNh0DWsSj/0Y8HO/RDkGXYn FDMj7fZSPKyPQPmEHg+W/KzxSSfdgWIHF2QaQ0b2q1wOSec4Rti52ohmNSY+KNIW/zODhugJ np3900V20aS7eD9K8GTU0TGC1pyz6IVJwIE= In-Reply-To: <173f0f7d804d3b0f33b6584b8a592d2079c593e9.camel@svanheule.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 5/15/26 14:10, Sander Vanheule wrote: > Adding back Guenter (and Wim) in Cc > > On Fri, 2026-05-15 at 20:48 +0000, Rustam Adilov wrote: >> On 2026-05-09 17:16, sashiko-bot@kernel.org wrote: >>> Thank you for your contribution! Sashiko AI review found 1 potential >>> issue(s) to consider: >>> - [High] Deadlock risk in the atomic restart handler due to regmap's >>> internal spinlock. >>> -- >>> >>> commit a520c8e2203154ba331a6ae28f00daec074e62ee >>> Author: Rustam Adilov >>> >>> watchdog: realtek-otto: Change to use regmap API >>> >>> This commit converts the realtek-otto watchdog driver to use the regmap API >>> instead of direct mmio accesses. It replaces direct read/modify/write >>> sequences with regmap functions and selects REGMAP_MMIO. >>> >>>> diff --git a/drivers/watchdog/realtek_otto_wdt.c >>>> b/drivers/watchdog/realtek_otto_wdt.c >>>> index 2c30ddd574c59..e5e9cb480f4f9 100644 >>>> --- a/drivers/watchdog/realtek_otto_wdt.c >>>> +++ b/drivers/watchdog/realtek_otto_wdt.c >>> [ ... ] >>>> @@ -199,7 +189,7 @@ static int otto_wdt_restart(struct watchdog_device >>>> *wdev, unsigned long reboot_m >>>> >>>>   /* Configure for shortest timeout and wait for reset to occur */ >>>>   v = FIELD_PREP(OTTO_WDT_CTRL_RST_MODE, reset_mode) | >>>> OTTO_WDT_CTRL_ENABLE; >>>> - iowrite32(v, ctrl->base + OTTO_WDT_REG_CTRL); >>>> + regmap_write(ctrl->regmap, OTTO_WDT_REG_CTRL, v); >>> >>> Could this regmap_write() cause a deadlock during system restart? >>> >>> The restart handler is often called during system shutdown or kernel panic >>> in an atomic context with local interrupts disabled. Since >>> devm_regmap_init_mmio() configures the regmap to use a spinlock by default, >>> if a panic occurs while another cpu holds the regmap lock (e.g., during >>> a ping or timeout update) and that cpu is halted by smp_send_stop(), this >>> regmap_write() could spin endlessly and prevent the system from rebooting. >>> >>> Additionally, on preempt-rt kernels, the regmap spinlock becomes a sleepable >>> rt_mutex, which could cause a sleeping in atomic context bug when acquired >>> with interrupts disabled. >>> >>>>   mdelay(3 * otto_wdt_tick_ms(ctrl, 0)); >>>> >> >> Hi Sander, >> >> I hope it is alright if i CCd you for this as i am not an expert on watchdog >> stuff. >> Wonna make sure this issue applies here before i proceed with the suggested >> solution >> to add .disable_locking to regmap_config without understanding the >> consequences of it. > > I'm no expert either, but AFAICT using .disable_locking would essentially mean > all accesses are only protected by the watchdog subsystem. Which is also the > case now, so that would mean feature parity. > > I'll leave it up to Guenter to decide if this refactor is worthwhile or not. > I don't mind the refactor, but it must not introduce a regression. As Sashiko points out, either regmap needs to be configured with .disable_locking set, or regmap can not be used in the restart handler. Guenter