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[80.7.220.175]) by smtp.gmail.com with ESMTPSA id h21sm3760283wmq.38.2021.07.02.12.10.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 02 Jul 2021 12:10:14 -0700 (PDT) Date: Fri, 2 Jul 2021 20:10:12 +0100 From: Daniel Thompson To: Lee Jones Cc: Yunus Bas , "stwiss.opensource@diasemi.com" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] mfd: mfd-core: Change "Failed to locate of_node" warning to debug Message-ID: <20210702191012.mecgw577ggkabxr6@maple.lan> References: <5a3f5fd82a391ade9a659338983e5efa7924210d.camel@phytec.de> <03cb3befabdda032b1ec9d97b4daac69fa23c759.camel@phytec.de> <5a718e7812f2ce46347ae94fda6175f38c65359e.camel@phytec.de> <20210630105557.eaktwdz5p6yzuron@maple.lan> <9b5d0003cce92cad57e7712d1e46c78c10f1a0ab.camel@phytec.de> <20210702125920.fydyfhwqe7tyr7oi@maple.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 02, 2021 at 07:36:07PM +0100, Lee Jones wrote: > On Fri, 02 Jul 2021, Daniel Thompson wrote: > > > On Thu, Jul 01, 2021 at 03:34:43PM +0000, Yunus Bas wrote: > > > Am Mittwoch, dem 30.06.2021 um 13:33 +0100 schrieb Lee Jones: > > > > On Wed, 30 Jun 2021, Daniel Thompson wrote: > > > > > > > > > On Wed, Jun 30, 2021 at 07:27:32AM +0000, Yunus Bas wrote: > > > > > > Am Dienstag, dem 29.06.2021 um 14:39 +0100 schrieb Lee Jones: > > > > > > Imagine only required parts of the MFD is connected to the > > > > > > designed > > > > > > system and unrequired parts are not. In that case, fully > > > > > > describing the > > > > > > MFD in the devicetree wouldn't represent the system at all. > > > > > > > > > > To describe hardware that is present but unused we would normally > > > > > use > > > > > status = "disabled". > > > > > > > > > > So if, for example, your board cannot use the RTC for some reason > > > > > (perhaps the board has no 32KHz oscillator?) then the DA9062 still > > > > > contains the hardware but it is useless. Such hardware could be > > > > > described as: > > > > > > > > > > da9062_rtc: rtc { > > > > >     compatible = "dlg,da9062-rtc"; > > > > >     status = "disabled"; > > > > > } > > > > > > > > > > Is this sufficient to suppress the warnings when the hardware is > > > > > not fully described? > > > > > > > > > > Right.  This is a potential solution. > > > > > > @Daniel, you hit the nail on the head :). Thank you for that. > > > > > > This solution would indeed surpress the warnings, but what is the > > > benefit of this? We would define never used device nodes just to > > > satisfy the driver. > > > > I would say that doing so resolves an awkward ambiguity of > > interpretation w.r.t. the bindings. > > > > 1. The MFD device compatible "dlg,da9062" tells the OS that we > > have an DA9062. An DA9062 contains six functions and this can be > > inferred *entirely* from the MFD compatible string. We do not > > need any subnodes to tell us that a DA9062 contains an RTC. The OS > > can (and in this case, does) already know that there is an RTC > > because we have a DA9062 (and a datasheet). > > > > 2. The default behaviour when a node has no status field is to > > assume that is is *enabled*. > > > > Based on #1 and #2 above then assuming that a DT that omits the > > sub-nodes actually means "disable the RTC" is risky. #2 might > > actually make it more natural to assume that the device is present and > > functional because there is no status field to tell MFD *not* to > > initialize it. > > Exactly. Nicely put. > > > That leaves us in a situation where there is no way to correctly guess > > the authors intent when sub-nodes are omitted from the DT. > > > Given this is something of a corner case and the documentation is > > ambiguous then a warning of the author does not clearly resolve the > > ambiguity seems reasonable. > > I'm having trouble parsing this part. That's quite reasonable because was is written is nonsense! Perhaps s/warning of the author/warning if the author/ will help but there are still too many words to say something very simple. The whole last paragraph could simply say: The bindings documentation is ambiguous so is it reasonable for the OS to issue a warning when the devicetree author does not clearly resolve the ambiguity. This is still a long sentence but at least it is no longer a complicated one! Daniel.