Message-ID: <97E2037C-3C3C-4B0B-8462-39B9E38CB3BB@aosc.io>
Date:   Mon, 23 Nov 2020 19:25:47 +0800
From:   Icenowy Zheng <icenowy@...c.io>
To:     Maxime Ripard <maxime@...no.tech>,
        Samuel Holland <samuel@...lland.org>
CC:     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?

>
>Maxime

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