Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751554AbdF1LZn (ORCPT ); Wed, 28 Jun 2017 07:25:43 -0400 Received: from mo4-p00-ob.smtp.rzone.de ([81.169.146.163]:36258 "EHLO mo4-p00-ob.smtp.rzone.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751469AbdF1LZg (ORCPT ); Wed, 28 Jun 2017 07:25:36 -0400 X-RZG-AUTH: :JGIXVUS7cutRB/49FwqZ7WcecEarQROEYabkiUo6mSAGQ+qKID8zPH8HfA== X-RZG-CLASS-ID: mo00 Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 9.3 \(3124\)) Subject: Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module From: "H. Nikolaus Schaller" In-Reply-To: <5bcc7ec0-4ae5-3703-3cee-ed644eef710a@samsung.com> Date: Wed, 28 Jun 2017 13:24:57 +0200 Cc: Hugues FRUCHET , Guennadi Liakhovetski , Rob Herring , Mark Rutland , Maxime Coquelin , Alexandre TORGUE , Mauro Carvalho Chehab , Hans Verkuil , devicetree , linux-arm-kernel , LKML , "linux-media@vger.kernel.org" , Benjamin Gaignard , Yannick FERTRE , Discussions about the Letux Kernel Message-Id: <9D51AC4C-6CB7-46A5-B363-2AD6DA6C497F@goldelico.com> References: <1498143942-12682-1-git-send-email-hugues.fruchet@st.com> <1498143942-12682-2-git-send-email-hugues.fruchet@st.com> <64e3005d-31df-71f2-762b-2c1b1152fc2d@st.com> <5cd25a47-f3be-8c40-3940-29f26a245076@kernel.org> <39501C78-7B81-4803-94C1-25DFA06EA526@goldelico.com> <6F68CD33-70E6-47C1-9E89-5E2AA776879F@goldelico.com> <5bcc7ec0-4ae5-3703-3cee-ed644eef710a@samsung.com> To: Sylwester Nawrocki X-Mailer: Apple Mail (2.3124) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id v5SBPpVj031471 Content-Length: 4249 Lines: 95 > Am 28.06.2017 um 12:50 schrieb Sylwester Nawrocki : > > On 06/28/2017 11:12 AM, H. Nikolaus Schaller wrote: >>> Am 28.06.2017 um 00:57 schrieb Sylwester Nawrocki : >>> On 06/27/2017 07:48 AM, H. Nikolaus Schaller wrote: >>>>> Am 26.06.2017 um 22:04 schrieb Sylwester Nawrocki : >>>>> On 06/26/2017 12:35 PM, Hugues FRUCHET wrote: >>>>>>> What I am missing to support the GTA04 camera is the control of the optional "vana-supply". >>>>>>> So the driver does not power up the camera module when needed and therefore probing fails. >>>>>>> >>>>>>> - vana-supply: a regulator to power up the camera module. >>>>>>> >>>>>>> Driver code is not complex to add: >>>>> >>>>>> Yes, I saw it in your code, but as I don't have any programmable power >>>>>> supply on my setup, I have not pushed this commit. >>>>> >>>>> Since you are about to add voltage supplies to the DT binding I'd suggest >>>>> to include all three voltage supplies of the sensor chip. Looking at the OV9650 >>>>> and the OV9655 datasheet there are following names used for the voltage supply >>>>> pins: >>>>> >>>>> AVDD - Analog power supply, >>>>> DVDD - Power supply for digital core logic, >>>>> DOVDD - Digital power supply for I/O. >>>> >>>> The latter two are usually not independently switchable from the SoC power >>>> the module is connected to. >>>> >>>> And sometimes DVDD and DOVDD are connected together. >>>> >>>> So the driver can't make much use of knowing or requesting them because the >>>> 1.8V supply is always active, even during suspend. >>>> >>>>> >>>>> I doubt the sensor can work without any of these voltage supplies, thus >>>>> regulator_get_optional() should not be used. I would just use the regulator >>>>> bulk API to handle all three power supplies. >>>> >>>> The digital part works with AVDD turned off. So the LDO supplying AVDD should >>>> be switchable to save power (&vaux3 on the GTA04 device).> >>>> But not all designs can switch it off. Hence the idea to define it as an >>>> /optional/ regulator. If it is not defined by DT, the driver simply assumes >>>> it is always powered on. >>> >>> I didn't say we can't define regulator supply properties as optional in the DT >>> binding. If we define them as such and any of these *-supply properties is >>> missing in DT with regulator_get() the regulator core will use dummy regulator >>> for that particular voltage supply. While with regulator_get_optional() >>> -ENODEV is returned when the regulator cannot be found. >> >> Ah, ok. I see. >> >> I had thought that it is the right thing to do like devm_gpiod_get_optional(). >> >> That one it is described as: >> >> "* This is equivalent to gpiod_get(), except that when no GPIO was assigned to >> * the requested function it will return NULL. This is convenient for drivers >> * that need to handle optional GPIOs." >> >> Seems to be inconsistent definition of what "optional" means. > > Indeed, this commit explains it further: > > commit de1dd9fd2156874b45803299b3b27e65d5defdd9 > regulator: core: Provide hints to the core about optional supplies > >> So we indeed should use devm_regulator_get() in this case. Thanks for > pointing out! > >>>> So in summary we only need AVDD switched for the GTA04 - but it does not >>>> matter if the others are optional properties. We would not use them. >>>> >>>> It does matter if they are mandatory because it adds DT complexity (size >>>> and processing) without added function. >>> >>> We should not be defining DT binding only with selected use cases/board >>> designs in mind. IMO all three voltage supplies should be listed in the >>> binding, presumably all can be made optional, with an assumption that when >>> the property is missing selected pin is hooked up to a fixed regulator. >> >> Ok, then it should just be defined in the bindings but not used by >> the driver? > > Yes, I think so. So we have a possibly complete binding right from the > beginning. I someone needs handling other supplies than AVDD they could > update the driver in future. Fine! I have sent some patches to Hughues so that he can integrate it in his next version of the patch series. BR and thanks, Nikolaus