Date: Tue, 3 Oct 2017 22:52:52 -0700 From: Russell Haley <russ.haley@gmail.com> To: Warner Losh <imp@bsdimp.com> Cc: Ian Lepore <ian@freebsd.org>, freebsd-arm <freebsd-arm@freebsd.org> Subject: Re: GENERIC kernel (was Re: BeagleBone Crochet Build Problem) Message-ID: <CABx9NuT1Jd5YuibU%2Bousg5JgiOwBQkw7txsR9vB90Gix622Xdw@mail.gmail.com> In-Reply-To: <CANCZdfqCtnjB4vXo7nQ7yH6uuaegT6jCxLtb5dbusqKtQ9jD=g@mail.gmail.com> References: <176dbdd5-1a32-06b2-7dd8-0647cc0fbe20@acm.org> <1506954050.22078.55.camel@freebsd.org> <CABx9NuS9XAfWNHM1fAFKV8byhWyv=jXS_W%2BNO3Y6s-CtEQdp6A@mail.gmail.com> <1506962766.22078.69.camel@freebsd.org> <20171003170053.GB2918@lonesome.com> <8eb57091-0b6f-3f0a-8c80-997b951a383f@acm.org> <CANCZdfr%2B7Kpz5Qqz46NHWV=9PgNGhf7nDo4m3UxN1pA6fzgjSA@mail.gmail.com> <1507068609.86205.81.camel@freebsd.org> <CANCZdfo0z%2B-NacmAwh3kB9cpFKzx%2B7emR7hEko8K63otiEXsNA@mail.gmail.com> <CABx9NuTnvPK7awiNF%2B7-CuuyuuBbuN=pKO_h25r0eVf3HLP=dw@mail.gmail.com> <CANCZdfqCtnjB4vXo7nQ7yH6uuaegT6jCxLtb5dbusqKtQ9jD=g@mail.gmail.com>
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On Tue, Oct 3, 2017 at 10:12 PM, Warner Losh <imp@bsdimp.com> wrote: > > > On Oct 3, 2017 9:50 PM, "Russell Haley" <russ.haley@gmail.com> wrote: > > On Tue, Oct 3, 2017 at 3:55 PM, Warner Losh <imp@bsdimp.com> wrote: >> On Tue, Oct 3, 2017 at 4:10 PM, Ian Lepore <ian@freebsd.org> wrote: >> >>> On Tue, 2017-10-03 at 14:55 -0600, Warner Losh wrote: >>> > On Tue, Oct 3, 2017 at 2:03 PM, Thomas Laus <lausts@acm.org> wrote: >>> > >>> > > >>> > > On 10/03/17 13:00, Mark Linimon wrote: >>> > > > >>> > > > On Mon, Oct 02, 2017 at 10:46:06AM -0600, Ian Lepore wrote: >>> > > > > >>> > > > > Why are we working towards a GENERIC kernel for arm? >>> > > > My intuition would be: >>> > > > >>> > > > - easier to tell new FreeBSD users how to start >>> > > > - less work for Release Engineering to make targets >>> > > > >>> > > > OTOH I'm not doing the work so I don't get to set the >>> > > > direction :-) >>> > > > >>> > > > My _opinion_ is that we still seem to have a steeper >>> > > > curve for our new users than is necessary. I intend to >>> > > > think about that more this fall. >>> > > > >>> > > That is probably 'wishful thinking' for the very distant future. >>> > > Most >>> > > of the common ARM SOC's have very different capabilities between each >>> > > other. Each also requires a unique U-Boot partition that gets read >>> > > before the FreeBSD kernel is loaded. >>> > > >>> > While this is true, how to create them can be described generically. >>> > You >>> > put these bits in this physical location, or on that partition and away >>> you >>> > go. The pre-boot environment is indeed different, but it's highly >>> desirable >>> > to have everything after that identical. It ensures uniformity in a >>> highly >>> > fragmented segment of our user base. Different kernels, even generated >>> from >>> > the same sources, run the risk of being subtly different from each >>> > other, >>> > leading to less coverage between the boards. We've had issues related >>> > to >>> > this in the past from time to time. >>> > >>> > I'm working on a program I'm calling "spin" which will take a >>> > description >>> > of what to use (eg, u-boot for the banana ramma board plus FreeBSD >>> > 12.3R) >>> > and it will create a bootable image knowing nothing more. If it also >>> > has >>> to >>> > know which of a bazillion kernels to use, that makes things more >>> > complicated. >>> > >>> > We want more uniformity, not less. Much of the differences we have >>> > today >>> > are arbitrary (and often wrong). >>> > >>> > >>> > > >>> > > I strongly favor the current approach that has a custom kernel >>> > > configuration file and U-Boot for each SOC. All of the common ARM >>> > > systems have a limited amount of real estate to store FreeBSD kernel >>> and >>> > > base system because it all must fit on a SD memory card. Having a >>> > > GENERIC kernel that covers all SOC variants would consume flash space >>> > > that will never be used. >>> > >>> > Nobody is saying that you can't do this. Just that GENERIC will be the >>> > union of all these kernel and be what you get by default. Since nobody >>> has >>> > quantified the differences, I'm having trouble getting worked up over >>> > the >>> > somewhat trivial difference in size (especially compared to most SD >>> > cards >>> > today). >>> > >>> > Warner >>> >>> Well, I guess I'll stop pretending there's any chance this freight >>> train can be stopped. I find the advantages mentioned so far dubious >>> at best, specious at worst, except for the single item "packaged base". >>> I don't know much about how that stuff is structured, but I can see >>> how having lots of different kernels might be difficult for packaging. >>> >>> But we absolutely have to solve the problem of making it easy for >>> people to create custom kernel configs. "Include GENERIC and add some >>> nodevice/nooption lines" is just not going to work. Right now I use >>> "include IMX6" and then some nodevice/nooption lines, and that works >>> fine. >>> >>> So if IMX6 goes away as a standalone buildable config, there needs to >>> be some other thing like it that can be included. The idea that keeps >>> nudging me is that our GENERIC should look like: >>> >>> include std.armv6 >>> include std.armdebug >>> include std.a10 >>> include std.a20 >>> include std.bcm2835 >>> include std.imx6 >>> ... >>> >>> Now anybody can create a custom config by including std.armv6, >>> std.armdebug if they want it, and their soc's std file. (The >>> std.armdebug is also for re@, so that it's easy for them to adjust when >>> making releases.) >>> >>> The problem is that I'm so backed up with other obbligations and >>> problem reports not getting dealt with and of course $work, so I never >>> find any time to give a scheme like this a try. >>> >> >> I welcome others to try to do this. You'll find it is a bit like peeling >> an >> onion. You don't have orthogonal classes so much as a venn diagram. I want >> to support ALL SoCs for the bcm2835 family? Or I just want to support one >> specific one. Allwinner makes this especially noticeable since it has a >> large family of things. And then do you slice the supported devices up via >> busses (only include those devices on PCI bus) vs device type (only >> include >> network devices). But then you get people wanting to have just wireless >> devices, or just USB wireless devices. You quickly discover a combinatoric >> explosion if you want to do this generically. >> >> I'll see if I can find some time take a shot at doing it just at the SoC >> level, but doing it generically gets really ugly really quickly.... >> Solving >> that specific problem doesn't look too awful. >> >> Warner > > My ignorance on this subject allows me to ask an obtuse question: Is > there no way to do something more dynamic and maintainable with > kldload and ubldr using scripts? As Warner has pointed out, there are > more arm variants, more manufacturers/SOM makers and more board > variants every year. Stuffing everything in and then "un-including" > everything doesn't sound maintainable. Even Ians suggestion may get > cumbersome in a short time. What if we actually do get good support > for Qualcom chips? Think of how many phone makers are there? > > > Someone would need to tag all the Fdt > > Drivers with PNP info first. > > Warner Can you point me to an example of the PNP tags or where to get more info? Would that mean modifying the DTS files (which I believe are now replicated from GNU libraries)? Russ
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