From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757375AbaHGJa4 (ORCPT ); Thu, 7 Aug 2014 05:30:56 -0400 Received: from mailout3.samsung.com ([203.254.224.33]:17783 "EHLO mailout3.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755303AbaHGJaw (ORCPT ); Thu, 7 Aug 2014 05:30:52 -0400 X-AuditID: cbfee68d-b7f2f6d0000062f0-93-53e3474844d8 From: Jingoo Han To: "'Thierry Reding'" , "'Bryan Wu'" , "'Lee Jones'" Cc: "'Rob Herring'" , "'Mark Rutland'" , "'Pawel Moll'" , "'Ian Campbell'" , "'Kumar Gala'" , "'Jean-Christophe Plagniol-Villard'" , "'Tomi Valkeinen'" , "'Russell King'" , "'Eric Miao'" , devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org, "'Jingoo Han'" , "'Ajay Kumar'" References: <1406806970-12561-1-git-send-email-thierry.reding@gmail.com> <20140731115429.GA12627@ulmo> In-reply-to: <20140731115429.GA12627@ulmo> Subject: Re: [RFC] pwm-backlight: Allow backlight to remain disabled on boot Date: Thu, 07 Aug 2014 18:30:47 +0900 Message-id: <009e01cfb222$4555d940$d0018bc0$%han@samsung.com> MIME-version: 1.0 Content-type: text/plain; charset=us-ascii Content-transfer-encoding: 7bit X-Mailer: Microsoft Office Outlook 12.0 Thread-index: Ac+stjT8hdopeKZZQ4GRVQcnKt/GbAFak0YQ Content-language: ko X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFtrBKsWRmVeSWpSXmKPExsVy+t8zQ10P98fBBr9f81gceH+QxeLozolM FvOPnGO12NF2nM2i/81CVotzr1YyWlxeeInV4v7Xo4wWmx5fY7U40feB1eLyrjlsFrcv81os vX6RyWLC9LUsFusevmCyaN17hN3i5655LBbr599icxDyWDNvDaNHS3MPm8flvl4mj52z7rJ7 rFz+hc3j1YU7LB6bVnWyedy5tofNY/OSeo++LasYPY7f2M7k8XmTXABPFJdNSmpOZllqkb5d AlfGruPqBb/4KnqvXmBsYHzG3cXIySEhYCJxbsUxZghbTOLCvfVsXYxcHEICyxglHsz7zQ5T dOvueiaIxCJGiWnXDkE5vxkl/rf2gLWzCahJfPlyGKxDRKBMYsb0M+wgRcwCV1kkPs25B9TB AdSRIfFkCVgNp4CWxKEFS5hAbGEBH4kb+9vB5rAIqErMn3IBrJxXwFbi1lxBkDCvgKDEj8n3 WEBsZqDW9TuPM0HY8hKb17xlBimXEFCXePRXF+ICI4mzpzYyQ5SISOx78Y4R5BoJgTccEk/W bIRaJSDxbfIhFoheWYlNB6ABISlxcMUNlgmMErOQbJ6FZPMsJJtnIVmxgJFlFaNoakFyQXFS epGhXnFibnFpXrpecn7uJkZIqundwXj7gPUhxmSg9ROZpUST84GpKq8k3tDYzMjC1MTU2Mjc 0ow0YSVx3qSHSUFCAumJJanZqakFqUXxRaU5qcWHGJk4OKUaGBViQn5t9PI1j302sfn5BiaG pMeMxUrJNhOkv2fr2t+7+fDws68HVecHXXc6EiXNbqM/Z8+WsnmdP5gCNJpflPcoq3IoaAtu EjQtmrTn6Fun4rtlBQ7sslUpP+bM93F8fWXT/PxQJckQltV8v3abhsX29y4W239KXkTLQ7Dg btLTxEquYuYZSizFGYmGWsxFxYkA+cDKG0sDAAA= X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFnrOKsWRmVeSWpSXmKPExsVy+t9jAV0P98fBBvc3sFsceH+QxeLozolM FvOPnGO12NF2nM2i/81CVotzr1YyWlxeeInV4v7Xo4wWmx5fY7U40feB1eLyrjlsFrcv81os vX6RyWLC9LUsFusevmCyaN17hN3i5655LBbr599icxDyWDNvDaNHS3MPm8flvl4mj52z7rJ7 rFz+hc3j1YU7LB6bVnWyedy5tofNY/OSeo++LasYPY7f2M7k8XmTXABPVAOjTUZqYkpqkUJq XnJ+SmZeuq2Sd3C8c7ypmYGhrqGlhbmSQl5ibqqtkotPgK5bZg7Qf0oKZYk5pUChgMTiYiV9 O0wTQkPcdC1gGiN0fUOC4HqMDNBAwjrGjF3H1Qt+8VX0Xr3A2MD4jLuLkZNDQsBE4tbd9UwQ tpjEhXvr2boYuTiEBBYxSky7dogJwvnNKPG/tYcZpIpNQE3iy5fD7CC2iECZxIzpZ9hBipgF rrJIfJpzD6iDA6gjQ+LJErAaTgEtiUMLloBtEBbwkbixvx1sDouAqsT8KRfAynkFbCVuzRUE CfMKCEr8mHyPBcRmBmpdv/M4E4QtL7F5zVtmkHIJAXWJR391IS4wkjh7aiMzRImIxL4X7xgn MArNQjJpFpJJs5BMmoWkZQEjyypG0dSC5ILipPRcQ73ixNzi0rx0veT83E2M4ET2TGoH48oG i0OMAhyMSjy8Fk2PgoVYE8uKK3MPMUpwMCuJ8FZbPw4W4k1JrKxKLcqPLyrNSS0+xGgK9OdE ZinR5Hxgks0riTc0NjEzsjQyszAyMTdXEuc90GodKCSQnliSmp2aWpBaBNPHxMEp1cA4JWEf W/2fJWxp3MJyD1MuCd6Rep7AULn97Pl9ZTsnJsU8XOntXal49Ym5z9ZDickx1/9fbFzLEWt5 /kAyq+h63w8LhTtjJL5NfR0/kaEkftNbjte/Lp1yO/Fg3UvWxGi1maUJBo9D7i/bcFa7ZLu3 OZO3j5g7h+KhptgLV5a4nNVdx/JwUoKCEktxRqKhFnNRcSIACJJ8InoDAAA= DLP-Filter: Pass X-MTR: 20000000000000000@CPGS X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thursday, July 31, 2014 8:55 PM, Thierry Reding wrote: > On Thu, Jul 31, 2014 at 01:42:50PM +0200, Thierry Reding wrote: > [...] > > @@ -317,6 +319,12 @@ static int pwm_backlight_probe(struct platform_device *pdev) > > } > > > > bl->props.brightness = data->dft_brightness; > > + > > + if (data->boot_off) > > + bl->props.power = FB_BLANK_POWERDOWN; > > + else > > + bl->props.power = FB_BLANK_UNBLANK; > > + > > backlight_update_status(bl); > > Looking at this again, perhaps a more sensible thing to do would be to > not call backlight_update_status() in the first place. For example if > the board defines that backlight should be kept off at boot, but the > bootloader had already enabled it, then this would effectively turn off > the backlight again. (+cc Ajay Kumar) Personally, I prefer not to call backlight_update_status(), when the backlight was already turned on by bootloader. Also, it would be better for subsystems such as DRM to handle the power of panel. > > I think it's safe to assume that if the bootloader sets up the backlight > then it would also set up the display. Therefore not touching the > backlight state at all at probe time seems like the safest default. > > Of course that doesn't help people who use some dumb framebuffer driver > and therefore nothing explicitly enables the backlight. So it would > still be changing behaviour for people for whom the bootloader doesn't > set up the backlight at all and who therefore rely on the kernel to turn > it on. > > We could perhaps alleviate that pain a little by making this dependent > on whether or not the board is booted using DT on the assumption that > anything that uses DT would be "modern" enough to provide a means to > automatically enable the backlight at the right moment. I also agree with the way to use DT. Best regards, Jingoo Han > > Thierry