Message-ID: <6367689.fsSILzYDoT@phil>
Date:   Thu, 25 May 2017 11:18:42 +0200
From:   Heiko Stuebner <heiko@...ech.de>
To:     Paul Kocialkowski <contact@...lk.fr>
Cc:     Doug Anderson <dianders@...omium.org>,
        Brian Norris <briannorris@...omium.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>
Subject: Re: [PATCH 1/3] ARM: dts: rockchip: Move cros-ec-sbs to rk3288-veyron-chromebook-sbs

Am Mittwoch, 24. Mai 2017, 16:38:39 CEST schrieb Paul Kocialkowski:
> Le mercredi 24 mai 2017 à 12:55 +0200, Heiko Stuebner a écrit :
> > Am Sonntag, 7. Mai 2017, 20:00:42 CEST schrieb Paul Kocialkowski:
> > > Hi,
> > > 
> > > Le lundi 01 mai 2017 à 08:49 -0700, Doug Anderson a écrit :
> > > > On Mon, May 1, 2017 at 7:07 AM, Heiko Stuebner <heiko@...ech.de> wrote:
> > > > > Am Sonntag, 30. April 2017, 22:56:52 CEST schrieb Paul Kocialkowski:
> > > > > > Le dimanche 30 avril 2017 à 22:37 +0200, Heiko Stuebner a écrit :
> > > > > > > Hi Paul,
> > > > > > > 
> > > > > > > Am Sonntag, 30. April 2017, 20:30:52 CEST schrieb Paul Kocialkowski:
> > > > > > > > This moves the cros-ec-sbs dtsi to a new rk3288-veyron-chromebook-
> > > > > > > > sbs
> > > > > > > > dtsi since it only concerns rk3288 veyron Chromebooks.
> > > > > > > > 
> > > > > > > > Other Chromebooks (such as the tegra124 nyans) also have sbs
> > > > > > > > batteries
> > > > > > > > and don't use this dtsi, that only makes sense when used with
> > > > > > > > rk3288-veyron-chromebook anyway.
> > > > > > > 
> > > > > > > That isn't true. The gru series (rk3399-based) also uses the
> > > > > > > sbs-battery [0]. And while it is currently limited to Rockchip-based
> > > > > > > Chromebooks it is nevertheless used on more than one platform, so
> > > > > > > the probability is high that it will be used in future series as
> > > > > > > well.
> > > > > > 
> > > > > > That's good to know, but as pointed out, other cros devices are using
> > > > > > a
> > > > > > sbs
> > > > > > battery without this header, so such a generic name isn't really a
> > > > > > good
> > > > > > fit.
> > > > 
> > > > It would be interesting to know if the "retry-count" ought to be the
> > > > same across all Chromebooks.  I guess you could argue that maybe
> > > > someone found it needed to be 10 in all "nyan" variants and needed to
> > > > be 1 in all "veyron" variants, but it seems more likely that the
> > > > difference is arbitrary, or that one of the two values would work for
> > > > everyone.  It sure looks like we've just been copying values from
> > > > device to device.  Given that all the "veyron" devices have vastly
> > > > different batteries (and probably all the nyan ones too), it seems
> > > > likely there ought to be one value.
> > > 
> > > Well, the retry-count is a maximum number of retries to detect a status
> > > change
> > > on external power connection/disconnection. From my experience, it seems
> > > that
> > > nyans do indeed more retries to detect the change than veyrons, on average.
> > > 
> > > I don't think setting this value to 1 is very reasonable (in the end, that's
> > > a
> > > number of seconds), because power supply status changes tend to take a few
> > > seconds to reflect on the battery status.
> > > 
> > > I think setting a high value (like 10) would always work and either way, the
> > > status detection mechanism stops itself as soon as a change is detected (it
> > > turns out this is not a good idea for bq27xxx batteries, because they go
> > > from
> > > charging to full in the first seconds after AC connection instead of
> > > directly
> > > reporting full, when full), but let's assume this is okay for sbs (and maybe
> > > change it later).
> > > 
> > > > In terms of setting the "charger", that also could potentially be
> > > > something that could be for all Chromebooks, or at least older ones
> > > > that don't have their charger implemented by the type C driver.  ...or
> > > > nyan devices could simply have a line in their dts like:
> > > > 
> > > > &battery {
> > > >   power-supplies = <&charger>;
> > > > };
> > > 
> > > That's true, but I think it makes as much sense to keep the whole binding.
> > > 
> > > In my opinion, the only reason to have a separate dtsi for this binding is
> > > that
> > > veyrons have another dtsi for chromebooks where this binding should be.
> > > However,
> > > it cannot be there because of minnie using another battery IC.
> > > 
> > > So my approach here would be to make it common for devices where other major
> > > parts are also common, so we can avoid duplication when most of the device-
> > > tree
> > > is already common. In cases where most of the device-tree is specific to a
> > > device, I think the binding should be duplicated. This is done already for
> > > lots
> > > of other components that could be made (somewhat) common anyway.
> > > 
> > > > 
> > > > > > Note that &charger has to be defined (after my subsequent patches),
> > > > > > which
> > > > > > it is
> > > > > > for devices that also include rk3288-veyron-chromebook, but not
> > > > > > necessarily
> > > > > > others.
> > > > > > 
> > > > > > Overall, I think having one -sbs dtsi file makes sense here because
> > > > > > there
> > > > > > is
> > > > > > already a rk3288-veyron-chromebook dtsi that veyron chromebooks use.
> > > > > > That
> > > > > > file
> > > > > > cannot contain the battery bindings because minnie has a different one
> > > > > > and
> > > > > > it
> > > > > > would be a bit silly to copy it over all devices. That definitely
> > > > > > makes
> > > > > > sense.
> > > > > > 
> > > > > > As for other devices, I don't see why we should have a separate
> > > > > > include
> > > > > > file for
> > > > > > the battery instead of having it in the device's dts. I think this
> > > > > > should
> > > > > > be the
> > > > > > case on gru/kevin.
> > > > > > 
> > > > > > Also maybe not *all* gru-based devices will turn out to use a SBS
> > > > > > battery,
> > > > > > so it
> > > > > > seems early to include this header in the gru dtsi.
> > > > 
> > > > For gru devices, we've moved to a "virtual sbs battery" provided by
> > > > the EC.  I'm not 100% positive that everything will just magically
> > > > work and be converted in the EC if we put a non-sbs battery on a board
> > > > with this EC feature, but I would hope we'd convert everything
> > > > properly.
> > > 
> > > Interesting and good to know!
> > > 
> > > > > > One last point, gru/kevin
> > > > > > currently don't define a charger, which will break my subsequent patch
> > > > > > (that is
> > > > > > however needed for the veyrons that use this file).
> > > > 
> > > > Arguably this should be fixed.  On veyron-chromebook we just use
> > > > "gpio-charger".  We didn't add a special charger driver w/ a property
> > > > like "ti,external-control" since the only piece of information that
> > > > Linux really needed from the charger was whether or not AC was
> > > > connected.
> > > 
> > > Thanks for taking that choice, it indeed makes things easier on the kernel
> > > side
> > > whith no drawbacks.
> > > 
> > > > 
> > > > > > To me, it seems that there's little advantage and major drawbacks in
> > > > > > keeping
> > > > > > this file the way it is.
> > > > > 
> > > > > I don't have any set opinion right now but after looking through the
> > > > > other uses of the sbs-battery the cros-ec-sbs.dtsi snippet really seems
> > > > > somewhat veyron/gru-specific - especially wrt. the retry-count values.
> > > > > 
> > > > > What I'm not sure about is whether it is actually better to keep the
> > > > > include
> > > > > around under a new name or just move the (rather tiny) sbs-battery node
> > > > > into the relevant devicetrees directly, when there aren't that many
> > > > > users
> > > > > anyway.
> > > > 
> > > > I'm fine with whatever you guys choose to do here.  It's nice not to
> > > > have copied "code", but with device tree sometimes copies are cleaner
> > > > than trying to share something.
> > > 
> > > I definitely agree. I think copies are a good fit here because overall, we
> > > have
> > > enough disparity in the possible configurations among different SoC
> > > platforms to
> > > justify having one per device. So I believe it would make sense to make that
> > > binding common *among the same SoC family*.
> > 
> > ok, so if I'm not mistaken it really looks like moving away from
> > cros-sbs-battery might be the easiest solution and with seeing the
> > different usages of the sbs-battery I tend to agree now :-) .
> > 
> > On the include vs. copy question it looks like we're tied as well with
> > mickey, minnie (and fievel + tiger from 2017) not using the sbs-battery
> > having local copies of the sbs-node in the affected devices really looks
> > like the best option.
> > 
> > So I guess we should get gru + the sbs veyron-devices their own sbs-battery
> > and then just drop te cros-ec-sbs.dtsi so that nobody else gets the idea
> > of using it.
> 
> How about keeping the nodes for veyron chromebooks (except minnie, which is a
> convertible anyway) in rk3288-veyron-chromebook-sbs as this patch initially
> suggested, in addition to changes to gru dts?

I'm only seeing a cluttered up dts directory with that, as the node
itself is only 9 lines (times 4 devices = 36 lines) and the copyright
header in the dtsi alone is 43 lines ;-) .

With the other includes (analog audio and sdmmc) they really save on
duplicate code, but the sbs node is so tiny and it looks like the arm32
dts directory will stay in that format for the forseeable future, that I'd
somehow prefer the sbs to move into the affected devices directly.


Heiko

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