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([2600:1700:e321:62f0:da43:aeff:fecc:bfd5]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-302978ad18asm1259151eec.26.2026.05.13.19.14.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 13 May 2026 19:14:21 -0700 (PDT) Sender: Guenter Roeck Message-ID: <045f1907-0180-46df-a123-cd0ce349e86b@roeck-us.net> Date: Wed, 13 May 2026 19:14:20 -0700 Precedence: bulk X-Mailing-List: linux-rtc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 4/5] hwmon: (pmbus/adm1266) replace probe-time RTC seed with rtc_class device To: Abdurrahman Hussain , Alexandru Tachici Cc: linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org, Alexandre Belloni , linux-rtc References: <20260512-adm1266-v3-0-a81a479b0bb0@nexthop.ai> <20260512-adm1266-v3-4-a81a479b0bb0@nexthop.ai> 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: <20260512-adm1266-v3-4-a81a479b0bb0@nexthop.ai> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 5/12/26 11:56, Abdurrahman Hussain wrote: > The driver currently writes the device's internal RTC at probe with > ktime_get_seconds(), which returns CLOCK_MONOTONIC seconds since boot > and is not a wall-clock value. The resulting timestamps embedded in > blackbox records are therefore meaningless across reboots, defeating > the cross-reboot record-correlation use case the field exists for. > > Switching the seed to ktime_get_real_seconds() does not actually fix > this: at probe the system wall clock may not yet have been set (no > external RTC, no userspace NTP), and seeding unconditionally also > clobbers whatever valid time the ADM1266 retained across a warm > reboot. > > The data sheet (Rev. D, p. 22) recommends "frequently send the time > stamp to the ADM1266 to synchronize the UNIX time and reduce the time > from drifting" when running on the internal oscillator. The clean way > to expose that policy is an rtc_class device backed by SET_RTC, so > that userspace tooling (hwclock, chrony, systemd-timesyncd) can drive > the re-sync against /dev/rtcN once it trusts the system clock - with > no driver-specific sysfs ABI. > > Drop the probe-time seed and adm1266_set_rtc() entirely. Add an > rtc_class device whose ->read_time and ->set_time callbacks read and > write the SET_RTC frame. The rtc_class API is second-precision, so > the SET_RTC fractional-seconds bytes are always written as zero. > This doesn't just set the RTC time, it also acts as a real-time-clock. That seems undesirable, since it isn't really a real-time clock. It would also be the first (pseudo) rtc residing outside the rtc subsystem. It seems to me that there must be a better solution. The rtc subsystem needs to be involved in this discussion. Note - as sent separately - that making this driver dependent on the RTC subsystem (as would be required by this patch) is unacceptable. Guenter > Fixes: 15609d189302 ("hwmon: (pmbus/adm1266) read blackbox") > Signed-off-by: Abdurrahman Hussain > --- > drivers/hwmon/pmbus/adm1266.c | 78 +++++++++++++++++++++++++++++++++++-------- > 1 file changed, 65 insertions(+), 13 deletions(-) > > diff --git a/drivers/hwmon/pmbus/adm1266.c b/drivers/hwmon/pmbus/adm1266.c > index 080e7dbd0c06..05b31bb08f38 100644 > --- a/drivers/hwmon/pmbus/adm1266.c > +++ b/drivers/hwmon/pmbus/adm1266.c > @@ -18,8 +18,8 @@ > #include > #include > #include "pmbus.h" > +#include > #include > -#include > > #define ADM1266_IC_DEVICE_REV 0xAE > #define ADM1266_BLACKBOX_CONFIG 0xD3 > @@ -517,21 +517,73 @@ static int adm1266_config_nvmem(struct adm1266_data *data) > return 0; > } > > -static int adm1266_set_rtc(struct adm1266_data *data) > +/* > + * SET_RTC frame layout (datasheet Rev. D, Table 84): > + * bytes [1:0] = fractional seconds, LSB = 1/65536 s > + * bytes [5:2] = seconds since 1970-01-01 UTC > + * The rtc_class API is second-precision, so the fractional bytes are > + * always written as zero. > + */ > +static int adm1266_write_rtc(struct i2c_client *client, time64_t secs) > { > - time64_t kt; > - char write_buf[6]; > + u8 buf[6] = { 0 }; > int i; > > - kt = ktime_get_seconds(); > + for (i = 0; i < 4; i++) > + buf[2 + i] = (secs >> (i * 8)) & 0xFF; > + > + return i2c_smbus_write_block_data(client, ADM1266_SET_RTC, sizeof(buf), buf); > +} > + > +static int adm1266_rtc_read_time(struct device *dev, struct rtc_time *tm) > +{ > + struct i2c_client *client = to_i2c_client(dev); > + u8 buf[I2C_SMBUS_BLOCK_MAX]; > + u32 secs; > + int ret; > + int i; > > - memset(write_buf, 0, sizeof(write_buf)); > + guard(pmbus_lock)(client); > + ret = i2c_smbus_read_block_data(client, ADM1266_SET_RTC, buf); > + if (ret < 0) > + return ret; > + if (ret != 6) > + return -EIO; > > + secs = 0; > for (i = 0; i < 4; i++) > - write_buf[2 + i] = (kt >> (i * 8)) & 0xFF; > + secs |= (u32)buf[2 + i] << (i * 8); > + > + rtc_time64_to_tm(secs, tm); > + return 0; > +} > > - return i2c_smbus_write_block_data(data->client, ADM1266_SET_RTC, sizeof(write_buf), > - write_buf); > +static int adm1266_rtc_set_time(struct device *dev, struct rtc_time *tm) > +{ > + struct i2c_client *client = to_i2c_client(dev); > + > + guard(pmbus_lock)(client); > + return adm1266_write_rtc(client, rtc_tm_to_time64(tm)); > +} > + > +static const struct rtc_class_ops adm1266_rtc_ops = { > + .read_time = adm1266_rtc_read_time, > + .set_time = adm1266_rtc_set_time, > +}; > + > +static int adm1266_register_rtc(struct adm1266_data *data) > +{ > + struct rtc_device *rtc; > + > + rtc = devm_rtc_allocate_device(&data->client->dev); > + if (IS_ERR(rtc)) > + return PTR_ERR(rtc); > + > + rtc->ops = &adm1266_rtc_ops; > + rtc->range_min = 0; > + rtc->range_max = U32_MAX; > + > + return devm_rtc_register_device(rtc); > } > > static int adm1266_probe(struct i2c_client *client) > @@ -557,10 +609,6 @@ static int adm1266_probe(struct i2c_client *client) > if (ret < 0) > return ret; > > - ret = adm1266_set_rtc(data); > - if (ret < 0) > - return ret; > - > ret = pmbus_do_probe(client, &data->info); > if (ret) > return ret; > @@ -569,6 +617,10 @@ static int adm1266_probe(struct i2c_client *client) > if (ret < 0) > return ret; > > + ret = adm1266_register_rtc(data); > + if (ret < 0) > + return ret; > + > adm1266_init_debugfs(data); > > return 0; >