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([2600:1700:e321:62f0:329c:23ff:fee3:9d7c]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-1fac156957fsm67709075ad.228.2024.07.01.10.21.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 01 Jul 2024 10:21:36 -0700 (PDT) Sender: Guenter Roeck Message-ID: <8a86272c-933d-45c2-b229-ed10e65d9053@roeck-us.net> Date: Mon, 1 Jul 2024 10:21:35 -0700 Precedence: bulk X-Mailing-List: linux-hwmon@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 02/10] 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: <20240628151346.1152838-1-linux@roeck-us.net> <20240628151346.1152838-3-linux@roeck-us.net> <615377cf-99bb-4159-b072-7992ccddf09d@cherry.de> <9fce6789-edc8-4c44-89c0-ae4ca3ec3315@roeck-us.net> <80a7f733-655e-4b00-a802-825d3acaafcb@roeck-us.net> <535f3381-2fa9-41a3-896a-8d5879546ac9@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: <535f3381-2fa9-41a3-896a-8d5879546ac9@cherry.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 7/1/24 09:13, Quentin Schulz wrote: > Hi Guenter, > > On 7/1/24 4:37 PM, Guenter Roeck wrote: >> On 7/1/24 07:11, Guenter Roeck wrote: >>> On 7/1/24 04:05, Quentin Schulz wrote: >>>> Hi Guenter, >>>> >>>> On 6/28/24 5:13 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. >>>>>  > Signed-off-by: Guenter Roeck >>>>> --- >>>>>   drivers/hwmon/amc6821.c | 6 +++--- >>>>>   1 file changed, 3 insertions(+), 3 deletions(-) >>>>> >>>>> diff --git a/drivers/hwmon/amc6821.c b/drivers/hwmon/amc6821.c >>>>> index 3c614a0bd192..e37257ae1a6b 100644 >>>>> --- a/drivers/hwmon/amc6821.c >>>>> +++ b/drivers/hwmon/amc6821.c >>>>> @@ -601,7 +601,7 @@ static ssize_t fan_show(struct device *dev, struct device_attribute *devattr, >>>>>       struct amc6821_data *data = amc6821_update_device(dev); >>>>>       int ix = to_sensor_dev_attr(devattr)->index; >>>>>       if (0 == data->fan[ix]) >>>>> -        return sprintf(buf, "0"); >>>>> +        return sprintf(buf, "6000000"); >>>>>       return sprintf(buf, "%d\n", (int)(6000000 / data->fan[ix])); >>>>>   } >>>>> @@ -625,10 +625,10 @@ static ssize_t fan_store(struct device *dev, struct device_attribute *attr, >>>>>       int ret = kstrtol(buf, 10, &val); >>>>>       if (ret) >>>>>           return ret; >>>>> -    val = 1 > val ? 0xFFFF : 6000000/val; >>>>> +    val = val < 1 ? 0xFFFF : 6000000 / val; >>>>>       mutex_lock(&data->update_lock); >>>>> -    data->fan[ix] = (u16) clamp_val(val, 1, 0xFFFF); >>>>> +    data->fan[ix] = (u16)clamp_val(val, 0, 0xFFFF); >>>> >>>> This is an unrelated change I believe and I would therefore have this in its own commit with proper documentation in the commit log. Indeed: >>>> >>>> 1- Change in fan_show handles the default 0x0 register value (which can only currently be achieved via the default value of the registers) >>>> 2- Allow (re-)setting unlimited fan speed by allowing the user to pass 6000001+ instead of clamping it to 6000000 RPM. >>>> >>> >>> Both changes are related. >>> >>> The whole point of this commit is to report and permit consistent values when >>> the register value is 0. But you do have a point - reading it after my changes >>> returns 6000000, but writing the same value sets the register to 1. So I think >>> the proper change would be to display 6000001 as speed if the register value is >>> 0, and provide a more detailed explanation. Would that address your concerns ? >>> >> >> Ah, never  mind, I'll do it differently: >> >> - If the register value is 0, keep reporting 0. > > Or...... maybe UINT_MAX? > Problem with that is that disconnected fans would report that value as fan speed. Traditionally drivers report a fan speed of 0 in that case. On the other side I agree that reporting "0" as "maximum fan speed" doesn't make much sense either because the real limit _is_ unlimited. But reporting 4294967295 in that case isn't really any better. >> - If the value written is 0, write 0, otherwise limit the range to 1..6000000 >>    and write clamp_val(6000000 / val, 1, 0xffff) >> > > Mmmm... I'm a bit worried about the implication of writing 0 in TACH-Low-Limit, what is actually going to happen in that scenario? I assume **every** possible RPM returned by TACH-DATA will be deemed invalid/below the limit then? Reading `Fan Spin-Up` section, if FSPD bit from register 0x20 (which we don't write to yet I think?) is set to 0, a spin-up is started whenever the fan is detected to be running at too low speed. And we would also be getting an interrupt for that too-low event. > > Basically, wondering if we shouldn't gate the writing of 0 to only the MAX setting? > Hmm, good point, and make sense. >> This minimizes user visibility of the changes, and also ensures that >> the reported fan speed is 0 if the register value is 0 when reading the fan >> speed. >> > > But didn't you say this means the fan is running at unknown 60 000 000+ RPMs? Do we really want to return 0 even if the fan is actually running? In which case max < current (possibly) but with no event happening (which I would expect, reading the datasheet). > Did I say that ? If so, I must have meant something different. The register counts the pulse period, so, yes, it would be 0 if rpm is above 6,000,000. But that is really not realistic. In practice I don't know what the controller reports in the register if no fan is connected - that would require real hardware which obviously I don't have. Overall I think I'll stick with the minimum, at least for now: Permit writing 0 into the high limit register only, and otherwise keep the currently permitted ranges. Thanks, Guenter