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smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mmB1wf01; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="mmB1wf01" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7683CC4CECE; Mon, 4 Nov 2024 11:47:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1730720842; bh=e1nzHk0cpcCIC/llfwkEOi5lrvUtOPMV7NJH5JG9+0k=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=mmB1wf01Pp6MR+T1Qs6Fb2/RhTQSvLDCOVKV9u+3AzczWUn7PpPA3NXh4IEnpFc4q mWH758J4t0LsSS0P2evQFY5lWwnpnH5z15/D9u1u5kIUlsWaQ+mtqY9w7AqZ1z9b0N Oel+V21OuqdUt5OWfWmp9YgffnXG6We0wFcTfEZ4Zvd/Wb/EkEli+NLuU67VfVo+CY jY+YHwpJimq/AXWBa5YCZh2oH3y24qFYfnKMGHPhDYv8WVRc/CWgOXcTDp2tGjDrjZ NMVLxEKZ7mAqG82nIEyXjaucK6osBJsk7gAzOC5UL43ctJrf3Y0brQx6OPX4PtYNuZ spq3GGEnX40Eg== Message-ID: <62e24ed4-3579-46ff-a77a-c5733125012c@kernel.org> Date: Mon, 4 Nov 2024 12:47:16 +0100 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 v2 2/2] dt-bindings: hwmon: pwm-fan: add retain-state-shutdown property To: Billy Tsai , Akinobu Mita Cc: "linux-kernel@vger.kernel.org" , "linux-hwmon@vger.kernel.org" , "devicetree@vger.kernel.org" , Jean Delvare , Guenter Roeck , Rob Herring , Krzysztof Kozlowski , Conor Dooley References: <20241026080535.444903-1-akinobu.mita@gmail.com> <20241026080535.444903-3-akinobu.mita@gmail.com> From: Krzysztof Kozlowski Content-Language: en-US Autocrypt: addr=krzk@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 04/11/2024 08:45, Billy Tsai wrote: >>> >>> On 28/10/2024 15:57, Akinobu Mita wrote: >>>>>>> >>>>>>> You described the desired Linux feature or behavior, not the actual >>>>>>> hardware. The bindings are about the latter, so instead you need to >>>>>>> rephrase the property and its description to match actual hardware >>>>>>> capabilities/features/configuration etc. >>>>>> >>>>>> Is this description okay? >>>>>> (Reused the description of retain-state-shutdown in leds-gpio.yaml) >>>>>> >>>>>> description: >>>>>> Retain the state of the PWM on shutdown. Useful in BMC systems, for >>>>>> example, when the BMC is rebooted while the host remains up, the fan >>>>>> will not stop. >>>>> >>>>> Nothing improved in the property. You still say what the system should >>>>> do. This is user-space choice, not DT. >>>> >>>> It seems better to implement it as a device attribute. >>> >>> I don't know about that. To repeat: if you say what system is supposed >>> to be doing, it is a policy. Describe the hardware and its configuration >>> and maybe this would be suitable for DT. > >> Billy, could you please write a proper description for this property? >> I'm not the right person for this. > > In our hardware, if the system reboots and power remains on the PWM controller > will retain its original settings. However, the pwm-fan.c driver currently disables > the PWM controller during a system reboot. I need this property to prevent pwm-fan.c If we change the PWM core not to disable it, then we have to change bindings? How is this binding applicable on system (e.g. on *BSD) which does not disable PWM on reboot? > from disabling the PWM when the system reboots. > In my point of view, the description can be: > Retain the state of the PWM on shutdown. Some platforms (e.g., BMC) will maintain > the PWM status after the system reboot. Add this property to prevent the PWM from being > disabled during the system reboot. You again describe what OS should do. First and last sentences are the same. Probably what you want to say is that fan is some critical component which should not be turned off or left unattended. Or that this hardware keeps last state of register on reset, so some boards might want to use it? If the first, then probably different property name. If the second, current seems fine, just choose some description describing actual hardware. Best regards, Krzysztof