From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bali.collaboradmins.com (bali.collaboradmins.com [148.251.105.195]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 34FB1230982; Tue, 10 Dec 2024 08:27:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.251.105.195 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733819228; cv=none; b=IH/D9HJWZDNgmQ6//TDS7dwmouiCF1y+5oOnSbnI0fkgqbNhIIxd86yw2jibTv3HA+2E74vqvTUK7fQKaiC16ct54QamRmzVaS6bQoiuVsqgtfIDfq14ah/pOEGq1e+Ynh0lm/oZ/rYmnkaJhYz1K4XilVAkorH41uFUdHCM2sA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733819228; c=relaxed/simple; bh=diwroXgDfFNnxf4klVn8zrbSRkjG62ZAQpvqL6XtdtE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=tzD5S6N7zLyMgk1GlpescHnxHmmraURCqs73F52/lmqh6D6CMny936aer6GjXeDuU+SBdlJG3CYARBnHzO1UuLh5OWTXvSVAt4LE1D1e7NLQrreRw71gT67pWuqsAgGHNy3jv63m4Y2Zqe9RxEMc3YZH2m41ELUGQBlRtTKVKyw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com; spf=pass smtp.mailfrom=collabora.com; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b=IG0T+9Xf; arc=none smtp.client-ip=148.251.105.195 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=collabora.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b="IG0T+9Xf" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1733819224; bh=diwroXgDfFNnxf4klVn8zrbSRkjG62ZAQpvqL6XtdtE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=IG0T+9XfaeyS+RmWBZiQT/og+j3HPF9nFz6CK4NPsOHhgFpI8wvAvqhLY2+AfcFnI XX3ruDPm/UTsUq9lRFNIrr0laPOLcOAGjFrrjPs3FUH6V1E9hqct5pmHaqcFYb8dkd 6qV4wYMsn0UGuIaSffJVdGrrS7RkAD05iZfEZeAuycO7fFudr600psv6F8GSBFjKjk 4oev1p2SP6tFhqSYtMW818wP6QFxPSdt73LQ7pXlzqyOAiimNfZVX+YUbX++aANZxg Yz1u6Upz3+nsCf0PG3yhvzHNL40Ij5bWmtoG4nsHgMl7lsvtgkIEk3T0bn5rTHkwsQ 0T6RsQFSn/uHw== Received: from [192.168.1.100] (2-237-20-237.ip236.fastwebnet.it [2.237.20.237]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: kholk11) by bali.collaboradmins.com (Postfix) with ESMTPSA id C026417E1323; Tue, 10 Dec 2024 09:27:03 +0100 (CET) Message-ID: <35392d9d-56a3-4db8-b500-6272d0bd275c@collabora.com> Date: Tue, 10 Dec 2024 09:27:02 +0100 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 1/4] arm64: dts: mediatek: mt8183-kukui-jacuzzi: Drop pp3300_panel voltage settings To: Chen-Yu Tsai Cc: Matthias Brugger , devicetree@vger.kernel.org, linux-mediatek@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Mark Brown References: <20241030070224.1006331-1-wenst@chromium.org> <20241030070224.1006331-2-wenst@chromium.org> From: AngeloGioacchino Del Regno Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Il 04/11/24 14:47, Chen-Yu Tsai ha scritto: > On Mon, Nov 4, 2024 at 9:19 PM AngeloGioacchino Del Regno > wrote: >> >> Il 04/11/24 14:00, Chen-Yu Tsai ha scritto: >>> On Wed, Oct 30, 2024 at 3:02 PM Chen-Yu Tsai wrote: >>>> >>>> The pp3300_panel fixed regulator is just a load switch. It does not have >>>> any regulating capabilities. Thus having voltage constraints on it is >>>> wrong. >>>> >>>> Remove the voltage constraints. >>>> >>>> Fixes: cabc71b08eb5 ("arm64: dts: mt8183: Add kukui-jacuzzi-damu board") >>>> Signed-off-by: Chen-Yu Tsai >>> >>> I see that the other three patches were merged and included in the pull >>> request, but not this one. Were there any concerns? >>> >> >> Sorry I forgot to actually provide an explanation for that - yes, I do have some >> comment about this one. >> >> Despite this being a load switch, it's still switching power from regulator A to >> target device X, so this is technically still providing 3.3V to device X. >> >> Think about how a "regular" full-fledged regulator works: you can (sometimes) set >> a voltage, and then you can ENABLE the VOUT for said regulator (/rail): this kind >> of "load switch" does exactly the same as the ENABLE switch for a full-fledged >> regulator. > > But it does not provide regulation. One cannot "set" the voltage on a load > switch; one can only set it on its upstream supply, if that supply provides > regulation. > > IIRC Mark said some years ago that if a regulator doesn't regulate the > voltage, then the voltage constraints should not be given. The constraints > are then derived from its upstream supply. > > That's the guideline I've followed for all the regulator related changes > I've done over the years. Does that work for you? > Ok, let's go with that then. There's only one problem - patches 2 to 4 don't apply for whatever reason, is there any dependency? Cheers, Angelo >> So, this is switching on and off a power rail that is derived from a source rail, >> practically creating... well, a "new" rail, with... >> >> VIN=somewhere-3.3v, >> VOUT=somewhere-still-3.3v >> >> Any objections/doubts/etc? :-) > > I agree with most of it, except the part that I laid out above about the > load switch not providing regulation. > >> P.S.: I'm writing fast, sorry if anything appears unclear, feel free to shoot more >> questions in case :-) > > No, it's pretty clear, and I believe one of the common interpretations > I see. Thank you for the quick response. > > > Thanks > ChenYu > >> Cheers, >> Angelo >> >>> >>> ChenYu >>> >>>> --- >>>> arch/arm64/boot/dts/mediatek/mt8183-kukui-jacuzzi.dtsi | 2 -- >>>> 1 file changed, 2 deletions(-) >>>> >>>> diff --git a/arch/arm64/boot/dts/mediatek/mt8183-kukui-jacuzzi.dtsi b/arch/arm64/boot/dts/mediatek/mt8183-kukui-jacuzzi.dtsi >>>> index 783c333107bc..7bbafe926558 100644 >>>> --- a/arch/arm64/boot/dts/mediatek/mt8183-kukui-jacuzzi.dtsi >>>> +++ b/arch/arm64/boot/dts/mediatek/mt8183-kukui-jacuzzi.dtsi >>>> @@ -35,8 +35,6 @@ pp1800_mipibrdg: pp1800-mipibrdg { >>>> pp3300_panel: pp3300-panel { >>>> compatible = "regulator-fixed"; >>>> regulator-name = "pp3300_panel"; >>>> - regulator-min-microvolt = <3300000>; >>>> - regulator-max-microvolt = <3300000>; >>>> pinctrl-names = "default"; >>>> pinctrl-0 = <&pp3300_panel_pins>; >>>> >>>> -- >>>> 2.47.0.163.g1226f6d8fa-goog >>>> >>