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 X-Spam-Level: X-Spam-Status: No, score=-4.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS, URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8F52BC43381 for ; Mon, 25 Mar 2019 02:45:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5756F2080F for ; Mon, 25 Mar 2019 02:45:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553481916; bh=GjnI2BEpx2hjKi1OtnX5B8pSFx7DJWOnCd0dIwqIFYs=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=fr03RJffHCAZIaiIqApzJDmLtBCb9hLmppp5g4UTq17HRhZr3DHG62LgOrIMKbpc4 ke7o0fC4fRLxapni00yyS/1IvxkqdZ4Egx4Cv5X7Ah4Fz3KDJPiMqjvj+Zo/rPwGI7 FFn6l81wSqYiT0nPK4KWWwRamqJe/JHR3MDAp/24= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729343AbfCYCpO (ORCPT ); Sun, 24 Mar 2019 22:45:14 -0400 Received: from mail.kernel.org ([198.145.29.99]:42440 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729154AbfCYCpN (ORCPT ); Sun, 24 Mar 2019 22:45:13 -0400 Received: from mail-wr1-f41.google.com (mail-wr1-f41.google.com [209.85.221.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9509A2133F; Mon, 25 Mar 2019 02:45:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553481912; bh=GjnI2BEpx2hjKi1OtnX5B8pSFx7DJWOnCd0dIwqIFYs=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=NZ9dER7WVNPPavbt/F9xodY0NRjFuV/h+hTIvDXi30nPM5GJYqozQFMd1BMZbyozN 4L6dYRYrdsD4n7Uqm7rc9yJUMxfVGfwiJhKn3HFmSL0HI7mVt+mT0cPRRrylj1V3lX wC94Upo82VynZJ6ta0Dh2vz0D1W2FG1K4CJbmEco= Received: by mail-wr1-f41.google.com with SMTP id y7so4185059wrn.11; Sun, 24 Mar 2019 19:45:12 -0700 (PDT) X-Gm-Message-State: APjAAAU1s72/vnua6o35IVU/n4qhU8Y5V1v8pVLJGek4a/Zw+TUHLETW Jvvw+/mfZHvs31OREqWw274UQ7QQIVu0vEiZSWk= X-Google-Smtp-Source: APXvYqwvMGbaGyoQM+3/IaCrgdEiqBCIa30TwwURzLC6MzbNa05CiucVG9duHaBC8KatdTtdEsmPwhUikShMV1UYu0M= X-Received: by 2002:adf:ec11:: with SMTP id x17mr13478902wrn.120.1553481911134; Sun, 24 Mar 2019 19:45:11 -0700 (PDT) MIME-Version: 1.0 References: <20190321084850.20769-1-wens@kernel.org> <20190321084850.20769-4-wens@kernel.org> <20190321093012.kg72voxs5kw5xtzu@flea> In-Reply-To: <20190321093012.kg72voxs5kw5xtzu@flea> From: Chen-Yu Tsai Date: Mon, 25 Mar 2019 10:45:01 +0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [linux-sunxi] Re: [PATCH v3 3/9] power: supply: axp20x_usb_power: allow disabling input current limiting To: Maxime Ripard Cc: Chen-Yu Tsai , Lee Jones , Sebastian Reichel , devicetree , linux-arm-kernel , "open list:THERMAL" , linux-kernel , linux-sunxi , Hans de Goede Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 21, 2019 at 5:30 PM Maxime Ripard wrote: > > Hi, > > The rest of the series is > Acked-by: Maxime Ripard > > On Thu, Mar 21, 2019 at 04:48:44PM +0800, Chen-Yu Tsai wrote: > > From: Chen-Yu Tsai > > > > The AXP PMICs allow the user to disable current limiting on the VBUS > > input. While read-out of this setting was already supported by the > > driver, it did not allow the user to configure the PMIC to disable > > current limiting. > > > > Add support for this. > > > > Signed-off-by: Chen-Yu Tsai > > Do we really want to do that though? That could have some pretty bad > consequences. If I understand the manual correctly, the PMIC has two mode of operation with regards to VBUS. Normal operation means the PMIC will try to limit the current draw to maintain VBUS above the set V_hold (defaults to 4.4V). This is in addition to the current limit set in this patch. The other mode of operation is bypass, where it ignores the voltage limit. Not sure if it also ignores the current limit, but probably not. In any case we don't support this mode in the driver. So I can think of a few cases where this might be bad: 1. High current draw results in excessive voltage drop and heating over line / traces due to insufficient conductor area. This should be covered by the voltage holding mechanism. 2. Over taxing the external power supply. This should also result in some voltage drop for simple power bricks. Advanced ones would either have current limiting or over-current protection. What bad consequences are you thinking of? ChenYu From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chen-Yu Tsai Subject: Re: Re: [PATCH v3 3/9] power: supply: axp20x_usb_power: allow disabling input current limiting Date: Mon, 25 Mar 2019 10:45:01 +0800 Message-ID: References: <20190321084850.20769-1-wens@kernel.org> <20190321084850.20769-4-wens@kernel.org> <20190321093012.kg72voxs5kw5xtzu@flea> Reply-To: wens-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: Sender: linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org In-Reply-To: <20190321093012.kg72voxs5kw5xtzu@flea> List-Post: , List-Help: , List-Archive: , List-Unsubscribe: , To: Maxime Ripard Cc: Chen-Yu Tsai , Lee Jones , Sebastian Reichel , devicetree , linux-arm-kernel , "open list:THERMAL" , linux-kernel , linux-sunxi , Hans de Goede List-Id: devicetree@vger.kernel.org On Thu, Mar 21, 2019 at 5:30 PM Maxime Ripard wrote: > > Hi, > > The rest of the series is > Acked-by: Maxime Ripard > > On Thu, Mar 21, 2019 at 04:48:44PM +0800, Chen-Yu Tsai wrote: > > From: Chen-Yu Tsai > > > > The AXP PMICs allow the user to disable current limiting on the VBUS > > input. While read-out of this setting was already supported by the > > driver, it did not allow the user to configure the PMIC to disable > > current limiting. > > > > Add support for this. > > > > Signed-off-by: Chen-Yu Tsai > > Do we really want to do that though? That could have some pretty bad > consequences. If I understand the manual correctly, the PMIC has two mode of operation with regards to VBUS. Normal operation means the PMIC will try to limit the current draw to maintain VBUS above the set V_hold (defaults to 4.4V). This is in addition to the current limit set in this patch. The other mode of operation is bypass, where it ignores the voltage limit. Not sure if it also ignores the current limit, but probably not. In any case we don't support this mode in the driver. So I can think of a few cases where this might be bad: 1. High current draw results in excessive voltage drop and heating over line / traces due to insufficient conductor area. This should be covered by the voltage holding mechanism. 2. Over taxing the external power supply. This should also result in some voltage drop for simple power bricks. Advanced ones would either have current limiting or over-current protection. What bad consequences are you thinking of? ChenYu 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 X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4B04DC43381 for ; Mon, 25 Mar 2019 02:45:44 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 18AF420896 for ; Mon, 25 Mar 2019 02:45:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="aHp+Uexd"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="NZ9dER7W" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 18AF420896 Authentication-Results: mail.kernel.org; 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Sun, 24 Mar 2019 19:45:12 -0700 (PDT) X-Gm-Message-State: APjAAAW8TyeD5Tpbni69OLFo/qFEK7/8If+sM3fMeJS0AljEoyWh7V0+ Gur+p1SQspCy5DsYZf79WuDYo2ySU7NFgT8QWDw= X-Google-Smtp-Source: APXvYqwvMGbaGyoQM+3/IaCrgdEiqBCIa30TwwURzLC6MzbNa05CiucVG9duHaBC8KatdTtdEsmPwhUikShMV1UYu0M= X-Received: by 2002:adf:ec11:: with SMTP id x17mr13478902wrn.120.1553481911134; Sun, 24 Mar 2019 19:45:11 -0700 (PDT) MIME-Version: 1.0 References: <20190321084850.20769-1-wens@kernel.org> <20190321084850.20769-4-wens@kernel.org> <20190321093012.kg72voxs5kw5xtzu@flea> In-Reply-To: <20190321093012.kg72voxs5kw5xtzu@flea> From: Chen-Yu Tsai Date: Mon, 25 Mar 2019 10:45:01 +0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [linux-sunxi] Re: [PATCH v3 3/9] power: supply: axp20x_usb_power: allow disabling input current limiting To: Maxime Ripard X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190324_194523_050088_0AA3663B X-CRM114-Status: GOOD ( 21.30 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: devicetree , "open list:THERMAL" , Sebastian Reichel , linux-kernel , Hans de Goede , linux-sunxi , Chen-Yu Tsai , Lee Jones , linux-arm-kernel Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Mar 21, 2019 at 5:30 PM Maxime Ripard wrote: > > Hi, > > The rest of the series is > Acked-by: Maxime Ripard > > On Thu, Mar 21, 2019 at 04:48:44PM +0800, Chen-Yu Tsai wrote: > > From: Chen-Yu Tsai > > > > The AXP PMICs allow the user to disable current limiting on the VBUS > > input. While read-out of this setting was already supported by the > > driver, it did not allow the user to configure the PMIC to disable > > current limiting. > > > > Add support for this. > > > > Signed-off-by: Chen-Yu Tsai > > Do we really want to do that though? That could have some pretty bad > consequences. If I understand the manual correctly, the PMIC has two mode of operation with regards to VBUS. Normal operation means the PMIC will try to limit the current draw to maintain VBUS above the set V_hold (defaults to 4.4V). This is in addition to the current limit set in this patch. The other mode of operation is bypass, where it ignores the voltage limit. Not sure if it also ignores the current limit, but probably not. In any case we don't support this mode in the driver. So I can think of a few cases where this might be bad: 1. High current draw results in excessive voltage drop and heating over line / traces due to insufficient conductor area. This should be covered by the voltage holding mechanism. 2. Over taxing the external power supply. This should also result in some voltage drop for simple power bricks. Advanced ones would either have current limiting or over-current protection. What bad consequences are you thinking of? ChenYu _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel