From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D0BAFC43334 for ; Mon, 18 Jul 2022 08:27:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233175AbiGRI1d (ORCPT ); Mon, 18 Jul 2022 04:27:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36122 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229890AbiGRI1b (ORCPT ); Mon, 18 Jul 2022 04:27:31 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e5ab]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AD70211A0C; Mon, 18 Jul 2022 01:27:30 -0700 (PDT) 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 madras.collabora.co.uk (Postfix) with ESMTPSA id 78F986601A08; Mon, 18 Jul 2022 09:27:27 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1658132848; bh=3wSuhWp2P2ZyIQrwtaWVzGC8uMFmX+0xQ1Qp+Gq760s=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=MEYN6sSMnl1b1jGZam3vGPUhszK6Kka5I6EgC7NQr3Q36fJmBTBNdXMzktsez5qIj y+s+XdM0YgKFkp9EXPOn+L1Cz+Oxd1XhKLcE2IBo0ISLE3PVkCNEzlzehYjysaiuWG Zo51GGkWRKk8PczsWqR8TmMapo+ER+hjgV4sjVLPFHsPVY4Qf/tMhapXsuArRIxERi 5Mf2Iqmq2tvvOG65/uZIKGF7a1cWG0Qn+VqDzTx0mD+1qYHnorumujxfSLaFnON56Z IAxKex2js5tEg95LQVFjSdehcwbr2FzRLtQrHYbNSh7clnBnGfAggQdU5fxiHr3DM+ lRudS6QdbjYdQ== Message-ID: Date: Mon, 18 Jul 2022 10:27:23 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH v5 13/13] video: backlight: mt6370: Add MediaTek MT6370 support Content-Language: en-US To: Daniel Thompson Cc: ChiaEn Wu , lee.jones@linaro.org, jingoohan1@gmail.com, pavel@ucw.cz, robh+dt@kernel.org, krzysztof.kozlowski+dt@linaro.org, matthias.bgg@gmail.com, sre@kernel.org, chunfeng.yun@mediatek.com, gregkh@linuxfoundation.org, jic23@kernel.org, lars@metafoo.de, lgirdwood@gmail.com, broonie@kernel.org, linux@roeck-us.net, heikki.krogerus@linux.intel.com, deller@gmx.de, chiaen_wu@richtek.com, alice_chen@richtek.com, cy_huang@richtek.com, dri-devel@lists.freedesktop.org, linux-leds@vger.kernel.org, devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, linux-usb@vger.kernel.org, linux-iio@vger.kernel.org, linux-fbdev@vger.kernel.org, szunichen@gmail.com References: <20220715112607.591-1-peterwu.pub@gmail.com> <20220715112607.591-14-peterwu.pub@gmail.com> <20220715162913.5ewxwhv6jtdgt3c2@maple.lan> From: AngeloGioacchino Del Regno In-Reply-To: <20220715162913.5ewxwhv6jtdgt3c2@maple.lan> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Il 15/07/22 18:29, Daniel Thompson ha scritto: > On Fri, Jul 15, 2022 at 02:38:45PM +0200, AngeloGioacchino Del Regno wrote: >> Il 15/07/22 13:26, ChiaEn Wu ha scritto: >>> From: ChiaEn Wu >>> >>> MediaTek MT6370 is a SubPMIC consisting of a single cell battery charger >>> with ADC monitoring, RGB LEDs, dual channel flashlight, WLED backlight >>> driver, display bias voltage supply, one general purpose LDO, and the >>> USB Type-C & PD controller complies with the latest USB Type-C and PD >>> standards. >>> >>> This adds support for MediaTek MT6370 Backlight driver. It's commonly used >>> to drive the display WLED. There are 4 channels inside, and each channel >>> supports up to 30mA of current capability with 2048 current steps in >>> exponential or linear mapping curves. >>> >>> Signed-off-by: ChiaEn Wu >> >> Hello ChiaEn, >> >> I propose to move this one to drivers/leds (or drivers/pwm) and, instead of >> registering a backlight device, register a PWM device. >> >> This way you will be able to reuse the generic backlight-pwm driver, as you'd >> be feeding the PWM device exposed by this driver to the generic one: this will >> most importantly make it easy to chain it with MTK_DISP_PWM (mtk-pwm-disp) >> with a devicetree that looks like... > > Out of interest, does MT6370 have the same structure for backlights as the prior > systems using mtk-pwm-disp or was mtk-pwm-disp simply a normal(-ish) PWM > that relied on something on the board for all the constant current > driver hardware? > > As per my understanding, mtk-pwm-disp is chained to other multimedia features of the display block of MediaTek SoCs, such as the AAL (adaptive ambient light), CABC (content adaptive backlight control) etc, other than being a normal(ish) PWM... that's the reason of my request. Moreover, in the end, this PMIC's backlight controller is just a "fancy" PWM controller, with OCP/OVP. >> >> pwmleds-disp { >> compatible = "pwm-leds"; >> >> disp_led: disp-pwm { >> label = "backlight-pwm"; >> pwms = <&pwm0 0 500000>; >> max-brightness = <1024>; >> }; >> }; >> >> backlight_lcd0: backlight { >> compatible = "led-backlight"; >> leds = <&disp_led>, <&pmic_bl_led>; >> default-brightness-level = <300>; >> }; > > I think this proposal has to start with the devicetree bindings rather > than the driver. Instead I think the question is: does this proposal > result in DT bindings that better describe the underlying hardware? > From how I understand it - yes: we have a fancy PWM (&pwm0) that we use to control display backlight (backlight-pwm)... Obviously, here we're not talking about OLEDs, but LCDs, where the backlight is made of multiple strings of WhiteLED (effectively, a "pwm-leds" controlled "led-backlight"). Using PWM will also allow for a little more fine-grained board specific configuration, as I think that this PMIC (and/or variants of it) will be used in completely different form factors: I think that's going to be both smartphones and tablets/laptops... and I want to avoid vendor properties to configure the PWM part in a somehow different way. > This device has lots of backlight centric features (OCP, OVP, single > control with multiple outputs, exponential curves, etc) and its not > clear where they would fit into the "PWM" bindings. > For OCP and OVP, the only bindings that fit would be regulators, but that's not a regulator... and that's about it - I don't really have arguments for that. What I really want to see here is usage of "generic" drivers like led_bl and/or pwm_bl as to get some "standardization" around with all the benefits that this carries. > Come to think of it I'm also a little worried also about the whole linear > versus exponential curve thing since I thought LED drivers were required > to use exponential curves. > That probably depends on how the controller interprets the data, I guess, but I agree with you on this thought. Regards, Angelo