Message-ID: <009A22D9-AF20-45C4-9674-13334B3EFFBA@aosc.io>
Date:   Mon, 23 Nov 2020 21:10:38 +0800
From:   Icenowy Zheng <icenowy@...c.io>
To:     maxime@...no.tech, Maxime Ripard <maxime@...no.tech>
CC:     Samuel Holland <samuel@...lland.org>, devicetree@...r.kernel.org,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        linux-sunxi@...glegroups.com, linux-kernel@...r.kernel.org,
        Chen-Yu Tsai <wens@...e.org>, Rob Herring <robh+dt@...nel.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [linux-sunxi] Re: [PATCH 3/3] arm64: allwinner: dts: a64: add DT for PineTab developer sample



于 2020年11月23日 GMT+08:00 下午8:53:32, Maxime Ripard <maxime@...no.tech> 写到:
>On Mon, Nov 23, 2020 at 07:25:47PM +0800, Icenowy Zheng wrote:
>> 
>> 
>> 于 2020年11月23日 GMT+08:00 下午7:15:12, Maxime Ripard <maxime@...no.tech>
>写到:
>> >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 = "PineTab Developer Sample";
>> >> >>>>>>> +	compatible = "pine64,pinetab-dev",
>"allwinner,sun50i-a64";
>> >> >>>>>>> +};
>> >> >>>>>>
>> >> >>>>>> Changing the DT and the compatible half-way through it
>isn't
>> >ok. Please
>> >> >>>>>> add a new DT with the newer revision like we did for the
>> >pinephone
>> >> >>>>>
>> >> >>>>> We did this on Pine H64.
>> >> >>>>
>> >> >>>> What are you referring to? I couldn't find a commit where we
>did
>> >what
>> >> >>>> you suggested in that patch to the pine H64.
>> >> >>>
>> >> >>> Oh the situation is complex. 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.
>Here
>> >the DT is always
>> >> >>> for the sample.
>> >> >>>
>> >> >>> 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".
>> >> >>
>> >> >> 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.
>> >This is
>> >> 
>> >> I don't think that was the intention at all. The DT was submitted
>for
>> >a
>> >> future product, whatever that future product ends up being at the
>> >time
>> >> of its release. Since there are necessarily no users until the
>> >product
>> >> ships, there is no chance of breaking users by modifying the DT.
>> >
>> >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
>> >> 
>> >> 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. Because if there any
>hardware
>> >> bugs fixed between initial upstreaming and production, the
>> >manufacture
>> >> must come up with a new DT name.
>> >> 
>> >> 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.
>> >> 
>> >> Do you want manufacturers to submit their initial board DT as
>> >> "$BOARD-prototype.dts", 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 $BOARD.dts, since the shipped board is
>> >*not*
>> >> the prototype) submit a "$BOARD.dts" to mainline?
>> >> 
>> >> 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. 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". We still have
>to
>> >support these users, whether we like it or not.
>> >
>> >> Without some guidance, or a change in policy, this problem is
>going
>> >to
>> >> keep coming up again and again.
>> >
>> >There's a few things that are interleaved here. First, there's two
>hard
>> >rules: never change the DT name and never change the compatible of a
>> >board.
>> >
>> >The former would break any build system, boot script or
>documentation,
>> >and the latter would break the DT compatibility.
>> >
>> >Aside from this, things get a bit blurrier since it's mostly about
>the
>> >intent. I'm fine with having a DT for a non-public prototype if it's
>> >clear from day one that it is. In this particular case, the DT just
>> >stated that support for the pinetab was added. I guess anyone would
>> >make
>> >the assumption without any context that this would be for the (or a)
>> >final design.
>> >
>> >Finally, I'd also advise against submitting the parts that are still
>> >not
>> >finalized though, because this is also fairly bad for the users.
>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. This means that any user that would use a kernel with
>that
>> >bugfix would have the display working, while rolling back to 5.9
>would
>> >break the display, even though everyone claimed it was supported
>> >out-of-the-box in mainline. This is a worse situation than not
>> >supporting the display in the first place here.
>> >
>> >> 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.
>> >
>> >Yes definitely. Pine devices may be worse though because of their
>> >policy
>> >of making their prototypes public. 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.
>> >
>> >> It's because they're actively involved in getting their
>> >> boards supported upstream. 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.
>> >
>> >I mean, it's not black and white either. 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.
>> >
>> >> I think Pine's behavior is something we want to encourage, not
>> >> penalize.
>> >
>> >For the DT in particular, yes
>> >
>> >> > Okay. But I'm not satisfied with a non-public sample occupies
>> >> > the pinetab name. 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.
>> >
>> >I understand where you're coming from, but the point I was making my
>> >previous mail is precisely that it's not really possible.
>> >
>> >You want to name the early adopter version _the_ production version.
>> >Let's assume the hardware changes again between the early adopter
>and
>> >mass-production version. 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. 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.
>> 
>> Then will it be okay to rename current pinetab DT to pinetab-sample
>and
>> then introduce new DTs all with suffixes?
>
>No. From my previous mail:

It can be seen as dropping the PineTab DT and introduce new DTs with suffix.

Do we have rule that we cannot drop boards?

>
>> > there's two hard rules: never change the DT name and never change
>> > the compatible of a board.
>> >
>> > The former would break any build system, boot script or
>> > documentation, and the latter would break the DT compatibility.
>
>Maxime

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