Date: Tue, 3 Oct 2017 21:50:41 -0700 From: Russell Haley <russ.haley@gmail.com> To: Warner Losh <imp@bsdimp.com> Cc: Ian Lepore <ian@freebsd.org>, "freebsd-arm@freebsd.org" <freebsd-arm@freebsd.org> Subject: Re: GENERIC kernel (was Re: BeagleBone Crochet Build Problem) Message-ID: <CABx9NuTnvPK7awiNF%2B7-CuuyuuBbuN=pKO_h25r0eVf3HLP=dw@mail.gmail.com> In-Reply-To: <CANCZdfo0z%2B-NacmAwh3kB9cpFKzx%2B7emR7hEko8K63otiEXsNA@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>
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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? Russhome | help
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