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([2600:1700:e321:62f0:329c:23ff:fee3:9d7c]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-1fb438a7890sm3713395ad.185.2024.07.04.10.50.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 04 Jul 2024 10:50:03 -0700 (PDT) Sender: Guenter Roeck Message-ID: Date: Thu, 4 Jul 2024 10:50:01 -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 02/11] hwmon: (amc6821) Make reading and writing fan speed limits consistent To: Quentin Schulz , linux-hwmon@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Farouk Bouabid References: <20240701212348.1670617-1-linux@roeck-us.net> <20240701212348.1670617-3-linux@roeck-us.net> <750d28c7-4d90-4bd6-a910-4d5e73828e55@cherry.de> <8cb9dc38-499e-4f10-93a4-c07898a776b4@roeck-us.net> <56ed417c-1dc2-474b-a2bc-5f17e1d2bd60@cherry.de> 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 CQgHAwIGFQgCCQoLBBYCAwECHgECF4ACGQEFAlVcphcFCRmg06EACgkQyx8mb86fmYFg0RAA nzXJzuPkLJaOmSIzPAqqnutACchT/meCOgMEpS5oLf6xn5ySZkl23OxuhpMZTVX+49c9pvBx hpvl5bCWFu5qC1jC2eWRYU+aZZE4sxMaAGeWenQJsiG9lP8wkfCJP3ockNu0ZXXAXwIbY1O1 c+l11zQkZw89zNgWgKobKzrDMBFOYtAh0pAInZ9TSn7oA4Ctejouo5wUugmk8MrDtUVXmEA9 7f9fgKYSwl/H7dfKKsS1bDOpyJlqhEAH94BHJdK/b1tzwJCFAXFhMlmlbYEk8kWjcxQgDWMu GAthQzSuAyhqyZwFcOlMCNbAcTSQawSo3B9yM9mHJne5RrAbVz4TWLnEaX8gA5xK3uCNCeyI sqYuzA4OzcMwnnTASvzsGZoYHTFP3DQwf2nzxD6yBGCfwNGIYfS0i8YN8XcBgEcDFMWpOQhT Pu3HeztMnF3HXrc0t7e5rDW9zCh3k2PA6D2NV4fews9KDFhLlTfCVzf0PS1dRVVWM+4jVl6l HRIAgWp+2/f8dx5vPc4Ycp4IsZN0l1h9uT7qm1KTwz+sSl1zOqKD/BpfGNZfLRRxrXthvvY8 BltcuZ4+PGFTcRkMytUbMDFMF9Cjd2W9dXD35PEtvj8wnEyzIos8bbgtLrGTv/SYhmPpahJA l8hPhYvmAvpOmusUUyB30StsHIU2LLccUPPOwU0ETofVZwEQALlLbQeBDTDbwQYrj0gbx3bq 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 JqvvP09whbqrABEBAAHCwWUEGAECAA8CGwwFAlVcpi8FCRmg08MACgkQyx8mb86fmYHNRQ/+ J0OZsBYP4leJvQF8lx9zif+v4ZY/6C9tTcUv/KNAE5leyrD4IKbnV4PnbrVhjq861it/zRQW cFpWQszZyWRwNPWUUz7ejmm9lAwPbr8xWT4qMSA43VKQ7ZCeTQJ4TC8kjqtcbw41SjkjrcTG wF52zFO4bOWyovVAPncvV9eGA/vtnd3xEZXQiSt91kBSqK28yjxAqK/c3G6i7IX2rg6pzgqh hiH3/1qM2M/LSuqAv0Rwrt/k+pZXE+B4Ud42hwmMr0TfhNxG+X7YKvjKC+SjPjqp0CaztQ0H nsDLSLElVROxCd9m8CAUuHplgmR3seYCOrT4jriMFBtKNPtj2EE4DNV4s7k0Zy+6iRQ8G8ng QjsSqYJx8iAR8JRB7Gm2rQOMv8lSRdjva++GT0VLXtHULdlzg8VjDnFZ3lfz5PWEOeIMk7Rj trjv82EZtrhLuLjHRCaG50OOm0hwPSk1J64R8O3HjSLdertmw7eyAYOo4RuWJguYMg5DRnBk WkRwrSuCn7UG+qVWZeKEsFKFOkynOs3pVbcbq1pxbhk3TRWCGRU5JolI4ohy/7JV1TVbjiDI HP/aVnm6NC8of26P40Pg8EdAhajZnHHjA7FrJXsy3cyIGqvg9os4rNkUWmrCfLLsZDHD8FnU mDW4+i+XlNFUPUYMrIKi9joBhu18ssf5i5Q= In-Reply-To: <56ed417c-1dc2-474b-a2bc-5f17e1d2bd60@cherry.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 7/4/24 00:52, Quentin Schulz wrote: > Hi Guenter, > > On 7/3/24 11:48 PM, Guenter Roeck wrote: >> On 7/3/24 07:35, Quentin Schulz wrote: >>> Hi Guenter, >>> >>> On 7/1/24 11:23 PM, Guenter Roeck wrote: >>>> The default value of the maximum fan speed limit register is 0, >>>> essentially translating to an unlimited fan speed. When reading >>>> the limit, a value of 0 is reported in this case. However, writing >>>> a value of 0 results in writing a value of 0xffff into the register, >>>> which is inconsistent. >>>> >>>> To solve the problem, permit writing a limit of 0 for the maximim fan >>>> speed, effectively translating to "no limit". Write 0 into the register >>>> if a limit value of 0 is written. Otherwise limit the range to >>>> <1..6000000> and write 1..0xffff into the register. This ensures that >>>> reading and writing from and to a limit register return the same value >>>> while at the same time not changing reported values when reading the >>>> speed or limits. >>>> >>>> While at it, restrict fan limit writes to non-negative numbers; writing >>>> a negative limit does not make sense and should be reported instead of >>>> being corrected. >>>> >>>> Signed-off-by: Guenter Roeck >>>> --- >>>> v2: Do not accept negative fan speed values >>>>      Display fan speed and speed limit as 0 if register value is 0 >>>>      (instead of 6000000), as in original code. >>>>      Only permit writing 0 (unlimited) for the maximum fan speed. >>>> >>>>   drivers/hwmon/amc6821.c | 13 +++++++++---- >>>>   1 file changed, 9 insertions(+), 4 deletions(-) >>>> >>>> diff --git a/drivers/hwmon/amc6821.c b/drivers/hwmon/amc6821.c >>>> index eb2d5592a41a..9c19d4d278ec 100644 >>>> --- a/drivers/hwmon/amc6821.c >>>> +++ b/drivers/hwmon/amc6821.c >>>> @@ -617,15 +617,20 @@ static ssize_t fan_store(struct device *dev, struct device_attribute *attr, >>>>   { >>>>       struct amc6821_data *data = dev_get_drvdata(dev); >>>>       struct i2c_client *client = data->client; >>>> -    long val; >>>> +    unsigned long val; >>>>       int ix = to_sensor_dev_attr(attr)->index; >>>> -    int ret = kstrtol(buf, 10, &val); >>>> +    int ret = kstrtoul(buf, 10, &val); >>>>       if (ret) >>>>           return ret; >>>> -    val = 1 > val ? 0xFFFF : 6000000/val; >>>> + >>>> +    /* The minimum fan speed must not be unlimited (0) */ >>>> +    if (ix == IDX_FAN1_MIN && !val) >>>> +        return -EINVAL; >>>> + >>>> +    val = val > 0 ? 6000000 / clamp_val(val, 1, 6000000) : 0; >>> >>> I'm wondering if we shouldn't check !val for min after this line instead? Otherwise we allow 6000001+RPM speeds... which is technically unlimited. >>> >> >> If ix == IDX_FAN1_MIN, val must be positive because of the check above. >> The expression "6000000 / clamp_val(val, 1, 6000000)" is therefore always >> positive as well because val is clamped. Its minimum result would be >> 6000000/6000000 = 1. The alternate case of the ternary expression would >> never hit because it is guaranteed that val > 0. Am I missing something ? >> > > No, I misread the code and I didn't see the clamp_val, which means we cannot have the denominator be > 6000000, meaning val cannot be 0 after that line (well, except if it is 0 **before** already). > > So no, just brain fart. > > Also, we probably could swap clamp_val(val, 1, 6000000) for min(val, 6000000) as val > 0 because of the ternary operator condition. But that's nothing important nor interesting. > Good point. I may do that if I have to send v4 (if I remember), but for now the existing code should be good enough. Thanks, Guenter