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([2600:1700:e321:62f0:da43:aeff:fecc:bfd5]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-74eb9f64c73sm14859060b3a.141.2025.07.16.12.01.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 16 Jul 2025 12:01:14 -0700 (PDT) Sender: Guenter Roeck Message-ID: <08cc0273-6c26-4ff1-b5fe-75235bca7a9f@roeck-us.net> Date: Wed, 16 Jul 2025 12:01:13 -0700 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] watchdog: sbsa: Adjust keepalive timeout to avoid MediaTek WS0 race condition To: Aaron Plattner , Wim Van Sebroeck Cc: linux-watchdog@vger.kernel.org, linux-kernel@vger.kernel.org, Timur Tabi References: <20250708233354.1551268-1-aplattner@nvidia.com> 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: <20250708233354.1551268-1-aplattner@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 7/8/25 16:33, Aaron Plattner wrote: > The MediaTek implementation of the sbsa_gwdt watchdog has a race > condition where a write to SBSA_GWDT_WRR is ignored if it occurs while > the hardware is processing a timeout refresh that asserts WS0. > > Detect this based on the hardware implementer and adjust wdd->timeout to > avoid the race. > > Signed-off-by: Aaron Plattner > Acked-by: Timur Tabi > --- > drivers/watchdog/sbsa_gwdt.c | 52 +++++++++++++++++++++++++++++++++--- > 1 file changed, 49 insertions(+), 3 deletions(-) > > diff --git a/drivers/watchdog/sbsa_gwdt.c b/drivers/watchdog/sbsa_gwdt.c > index 5f23913ce3b4..81012dbe9088 100644 > --- a/drivers/watchdog/sbsa_gwdt.c > +++ b/drivers/watchdog/sbsa_gwdt.c > @@ -75,11 +75,17 @@ > #define SBSA_GWDT_VERSION_MASK 0xF > #define SBSA_GWDT_VERSION_SHIFT 16 > > +#define SBSA_GWDT_IMPL_MASK 0x7FF > +#define SBSA_GWDT_IMPL_SHIFT 0 > +#define SBSA_GWDT_IMPL_MEDIATEK 0x426 > + > /** > * struct sbsa_gwdt - Internal representation of the SBSA GWDT > * @wdd: kernel watchdog_device structure > * @clk: store the System Counter clock frequency, in Hz. > * @version: store the architecture version > + * @need_ws0_race_workaround: > + * indicate whether to adjust wdd->timeout to avoid a race with WS0 > * @refresh_base: Virtual address of the watchdog refresh frame > * @control_base: Virtual address of the watchdog control frame > */ > @@ -87,6 +93,7 @@ struct sbsa_gwdt { > struct watchdog_device wdd; > u32 clk; > int version; > + bool need_ws0_race_workaround; > void __iomem *refresh_base; > void __iomem *control_base; > }; > @@ -161,6 +168,31 @@ static int sbsa_gwdt_set_timeout(struct watchdog_device *wdd, > */ > sbsa_gwdt_reg_write(((u64)gwdt->clk / 2) * timeout, gwdt); > > + /* > + * Some watchdog hardware has a race condition where it will ignore > + * sbsa_gwdt_keepalive() if it is called at the exact moment that a > + * timeout occurs and WS0 is being asserted. Unfortunately, the default > + * behavior of the watchdog core is very likely to trigger this race > + * when action=0 because it programs WOR to be half of the desired > + * timeout, and watchdog_next_keepalive() chooses the exact same time to > + * send keepalive pings. > + * > + * This triggers a race where sbsa_gwdt_keepalive() can be called right > + * as WS0 is being asserted, and affected hardware will ignore that > + * write and continue to assert WS0. After another (timeout / 2) > + * seconds, the same race happens again. If the driver wins then the > + * explicit refresh will reset WS0 to false but if the hardware wins, > + * then WS1 is asserted and the system resets. > + * > + * Avoid the problem by scheduling keepalive heartbeats one second > + * earlier than the WOR timeout. > + * > + * This workaround might not be needed in a future revision of the > + * hardware. > + */ > + if (gwdt->need_ws0_race_workaround) > + wdd->timeout -= 2; > + It seems to me that this is still racy. If the ping is ignored, I would assume that this is reflected in the watchdog registers. How about reading the status if the workaround is needed and issuing another keepalive if it was ignored ? Or just always issue a second write to SBSA_GWDT_WRR in that case, maybe after some short delay ? Guenter