Date: Tue, 3 Oct 2017 14:55:07 -0600 From: Warner Losh <imp@bsdimp.com> To: lausts@acm.org Cc: "freebsd-arm@freebsd.org" <freebsd-arm@freebsd.org> Subject: Re: GENERIC kernel (was Re: BeagleBone Crochet Build Problem) Message-ID: <CANCZdfr%2B7Kpz5Qqz46NHWV=9PgNGhf7nDo4m3UxN1pA6fzgjSA@mail.gmail.com> In-Reply-To: <8eb57091-0b6f-3f0a-8c80-997b951a383f@acm.org> 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>
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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
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