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Subject: Re: [linux-sunxi] Re: [PATCH 3/3] arm64: allwinner: dts: a64: add DT for PineTab developer sample
To:     Maxime Ripard <maxime@cerno.tech>,
        Samuel Holland <samuel@sholland.org>
CC:     devicetree@vger.kernel.org,
        Jernej Skrabec <jernej.skrabec@siol.net>,
        linux-sunxi@googlegroups.com, linux-kernel@vger.kernel.org,
        Chen-Yu Tsai <wens@csie.org>, Rob Herring <robh+dt@kernel.org>,
        linux-arm-kernel@lists.infradead.org
From:   Icenowy Zheng <icenowy@aosc.io>
Message-ID: <97E2037C-3C3C-4B0B-8462-39B9E38CB3BB@aosc.io>
Precedence: bulk


=E4=BA=8E 2020=E5=B9=B411=E6=9C=8823=E6=97=A5 GMT+08:00 =E4=B8=8B=E5=8D=88=
7:15:12, Maxime Ripard <maxime@cerno=2Etech> =E5=86=99=E5=88=B0:
>Hi!
>
>On Fri, Nov 20, 2020 at 08:51:48PM -0600, Samuel Holland wrote:
>> On 11/20/20 5:30 PM, Icenowy Zheng wrote:
>> >>>>>>> +/ {
>> >>>>>>> +	model =3D "PineTab Developer Sample";
>> >>>>>>> +	compatible =3D "pine64,pinetab-dev", "allwinner,sun50i-a64";
>> >>>>>>> +};
>> >>>>>>
>> >>>>>> Changing the DT and the compatible half-way through it isn't
>ok=2E Please
>> >>>>>> add a new DT with the newer revision like we did for the
>pinephone
>> >>>>>
>> >>>>> We did this on Pine H64=2E
>> >>>>
>> >>>> What are you referring to? I couldn't find a commit where we did
>what
>> >>>> you suggested in that patch to the pine H64=2E
>> >>>
>> >>> Oh the situation is complex=2E On Pine H64, we didn't specify
>anything at
>> >>> start (which is the same here), the DT is originally
>version-neutral
>> >>> but then transitioned to model B, then reverted to model A=2E Here
>the DT is always
>> >>> for the sample=2E
>> >>>
>> >>> However, for Pine H64 there's model A/B names, but for PineTab
>there's no
>> >>> any samples that are sold, thus except who got the samples, all
>PineTab
>> >>> owners simply owns a "PineTab", not a "PineTab xxx version"=2E
>> >>
>> >> It's fairly simple really, we can't really predict the future, so
>any DT
>> >> submitted is for the current version of whatever board there is=2E
>This is
>>=20
>> I don't think that was the intention at all=2E The DT was submitted for
>a
>> future product, whatever that future product ends up being at the
>time
>> of its release=2E Since there are necessarily no users until the
>product
>> ships, there is no chance of breaking users by modifying the DT=2E
>
>There was no indication of that in the commit though
>
>> >> what we (somewhat messily) did for the PineH64, for the pinephone,
>or
>> >> really any other board that has several revisions
>>=20
>> Surely a non-public prototype doesn't count as a separate revision!
>This
>> sort of policy strongly discourages ever shipping a board with
>> out-of-the-box mainline Linux support=2E Because if there any hardware
>> bugs fixed between initial upstreaming and production, the
>manufacture
>> must come up with a new DT name=2E
>>=20
>> This is hostile to the users as well, because the "canonical" DT name
>no
>> longer matches the "canonical" (read: the only one ever available)
>> version of the hardware=2E
>>=20
>> Do you want manufacturers to submit their initial board DT as
>> "$BOARD-prototype=2Edts", just in case they have to make a change
>before
>> production? And only after the board is shipped (with out-of-tree
>> patches, of course, to use $BOARD=2Edts, since the shipped board is
>*not*
>> the prototype) submit a "$BOARD=2Edts" to mainline?
>>=20
>> Maxime, can you clarify specifically what the line is where a device
>> tree is "locked down" and further changes to the hardware require a
>new
>> name? First sample leaves the factory? $NUMBER units produced? First
>> sold to the public for money?
>
>The first board that is shipped to a user=2E From the wiki, the version
>supported here (I guess?) has been shipped to around 100 people, so it
>doesn't really qualify for the "non-public prototype"=2E We still have to
>support these users, whether we like it or not=2E
>
>> Without some guidance, or a change in policy, this problem is going
>to
>> keep coming up again and again=2E
>
>There's a few things that are interleaved here=2E First, there's two hard
>rules: never change the DT name and never change the compatible of a
>board=2E
>
>The former would break any build system, boot script or documentation,
>and the latter would break the DT compatibility=2E
>
>Aside from this, things get a bit blurrier since it's mostly about the
>intent=2E I'm fine with having a DT for a non-public prototype if it's
>clear from day one that it is=2E In this particular case, the DT just
>stated that support for the pinetab was added=2E I guess anyone would
>make
>the assumption without any context that this would be for the (or a)
>final design=2E
>
>Finally, I'd also advise against submitting the parts that are still
>not
>finalized though, because this is also fairly bad for the users=2E Let's
>take the current situation as the example: from what I understand, the
>screen changed half-way through the process, and the first one was
>upstreamed=2E This means that any user that would use a kernel with that
>bugfix would have the display working, while rolling back to 5=2E9 would
>break the display, even though everyone claimed it was supported
>out-of-the-box in mainline=2E This is a worse situation than not
>supporting the display in the first place here=2E
>
>> You'll note that so far it has mostly affected Pine devices, and I
>don't
>> think that's because they make more board revisions than other
>> manufacturers=2E
>
>Yes definitely=2E Pine devices may be worse though because of their
>policy
>of making their prototypes public=2E I guess most of the issues we had
>also were due to poor communication: context on what were the Pine
>intentions were missing, and thus we couldn't catch things that turned
>out to be bad later on during review=2E
>
>> It's because they're actively involved in getting their
>> boards supported upstream=2E For other manufacturers, it's some user
>> sending in a device tree months after the hardware ships to the
>public
>> -- of course the hardware is more stable at that point=2E
>
>I mean, it's not black and white either=2E One could very well send the
>DT
>once the final design is done and that would still be upstreamed way
>before reaching the first user=2E
>
>> I think Pine's behavior is something we want to encourage, not
>> penalize=2E
>
>For the DT in particular, yes
>
>> > Okay=2E But I'm not satisfied with a non-public sample occupies
>> > the pinetab name=2E Is rename it to pinetab-dev and add a
>> > pinetab-retail okay?
>>
>> To me, naming the production version anything but "pinetab" isn't
>> satisfying either=2E
>
>I understand where you're coming from, but the point I was making my
>previous mail is precisely that it's not really possible=2E
>
>You want to name the early adopter version _the_ production version=2E
>Let's assume the hardware changes again between the early adopter and
>mass-production version=2E Which one will be _the_ production version?
>The
>early-adopter or the mass-produced one?
>
>There's really no good answer here, and both would suck in their own
>way=2E The only way to deal with this is to simply avoid defining one
>version as the one true board, and just loading the proper DT in u-boot
>based on whatever clue we have of the hardware revision=2E


Then will it be okay to rename current pinetab DT to pinetab-sample and
then introduce new DTs all with suffixes?

>
>Maxime