From: Daniel Thompson <daniel.thompson@linaro.org>
To: Lee Jones <lee.jones@linaro.org>
Cc: Yunus Bas <Y.Bas@phytec.de>,
"stwiss.opensource@diasemi.com" <stwiss.opensource@diasemi.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mfd: mfd-core: Change "Failed to locate of_node" warning to debug
Date: Fri, 2 Jul 2021 20:10:12 +0100 [thread overview]
Message-ID: <20210702191012.mecgw577ggkabxr6@maple.lan> (raw)
In-Reply-To: <YN9cl1/7k/UlllSq@dell>
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?
> > <snip>
> > > >
> > > > 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.
next prev parent reply other threads:[~2021-07-02 19:10 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-16 8:19 [PATCH] mfd: mfd-core: Change "Failed to locate of_node" warning to debug Yunus Bas
2021-06-16 9:03 ` Lee Jones
2021-06-17 7:46 ` Yunus Bas
2021-06-17 8:27 ` Lee Jones
2021-06-29 7:25 ` Yunus Bas
2021-06-29 9:07 ` Lee Jones
2021-06-29 9:41 ` Yunus Bas
2021-06-29 13:39 ` Lee Jones
2021-06-30 7:27 ` Yunus Bas
2021-06-30 8:42 ` Lee Jones
2021-06-30 10:55 ` Daniel Thompson
2021-06-30 12:33 ` Lee Jones
2021-07-01 15:34 ` Yunus Bas
2021-07-01 16:45 ` Lee Jones
2021-07-02 12:59 ` Daniel Thompson
2021-07-02 18:36 ` Lee Jones
2021-07-02 19:10 ` Daniel Thompson [this message]
2021-07-05 7:24 ` Yunus Bas
2021-07-05 7:31 ` Lee Jones
2021-07-05 7:50 ` Yunus Bas
2021-07-05 8:05 ` Lee Jones
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