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([2600:1700:e321:62f0:da43:aeff:fecc:bfd5]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7a414012bcesm8972989b3a.8.2025.10.27.09.52.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 27 Oct 2025 09:52:56 -0700 (PDT) Sender: Guenter Roeck Message-ID: Date: Mon, 27 Oct 2025 09:52:53 -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 v2 2/2] hwmon: Add TSC1641 I2C power monitor driver To: Igor Reznichenko Cc: conor+dt@kernel.org, corbet@lwn.net, david.hunter.linux@gmail.com, devicetree@vger.kernel.org, krzk+dt@kernel.org, linux-doc@vger.kernel.org, linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org, robh@kernel.org, skhan@linuxfoundation.org References: <20251027064127.648712-1-igor@reznichenko.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: <20251027064127.648712-1-igor@reznichenko.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 10/26/25 23:41, Igor Reznichenko wrote: >> In some way this is inconsistent: It accepts a shunt resistor value of, say, 105 >> even though the chip can only accept multiples of 10 uOhm. In situations like this >> I suggest to expect devicetree values to be accurate and to clamp values entered >> through sysfs. More on that below. >> >>> + return 0; >>> +} >>> + >>> +static int tsc1641_set_shunt(struct tsc1641_data *data, u32 val) >>> +{ >>> + struct regmap *regmap = data->regmap; >>> + long rshunt_reg; >>> + >>> + if (tsc1641_validate_shunt(val) < 0) >>> + return -EINVAL; >>> + >>> + data->rshunt_uohm = val; >>> + data->current_lsb_ua = DIV_ROUND_CLOSEST(TSC1641_VSHUNT_LSB_NVOLT * 1000, >>> + data->rshunt_uohm); >>> + /* RSHUNT register LSB is 10uOhm so need to divide further*/ >>> + rshunt_reg = DIV_ROUND_CLOSEST(data->rshunt_uohm, TSC1641_RSHUNT_LSB_UOHM); >> >> This means that all calculations do not use the actual shunt resistor values used >> by the chip, but an approximation. I would suggest to store and use the actual shunt >> resistor value instead, not the one entered by the user. > > By "actual shunt" you mean defined in devicetree? Then does it mean disabling > writing value by user via sysfs and making "shunt_resistor" read-only or leaving it > writable and clamping to devicetree value, thus discarding the user provided value? > I said "used by the chip", and referred to the value written into TSC1641_RSHUNT_LSB_UOHM. >> See below - clamping is insufficient for negative values, and it is not clear to me if >> the limit register is signed or unsigned. > >> Also, the datasheet doesn't say that the limit value would be signed. Did you verify >> that negative temperature limit values are actually treated as negative values ? > > SUL, SOL, TOL are signed, I verified. The negative limits for current and temperature > work well based on my testing. > Please add a respective comment into the code. >> This doesn't work as intended for negative values. regmap doesn't expect to see >> negative register values and returns an error if trying to write one, so clamping >> against SHRT_MIN and SHRT_MAX is insufficient. You also need to mask the result >> against 0xffff. > > I was under impression regmap would handle this masking correctly when defining > .val_bits = 16. E.g. in regmap.c:973 it selects formatting function for 16bit values. > I can mask explicitly if it's required. > It certainly doesn't throw error since negative alerts work as mentioned. > My unit test code bails out on negative values, returning an error from regmap when trying to write negative values. I had seen that before. Masking the value passed to regmap with 0xffff solved the problem. >> Why did you choose lcrit/crit attributes instead of min/max ? If there is only >> one alert limit, that usually means the first level of alert, not a critical level. >> Raising an alert does not mean it is a critical alert. Please reconsider. > > I used hwmon/ina2xx.c as a reference. It covers many similar power monitors which > have single threshold alerts and defines only lcrit/crit. If this is a wrong approach > I'll change to min/max. Isn't that great ? You can always find an example for everything in the Linux kernel if you are looking for it. Guenter