Hi Rob, On Mon, 3 Dec 2018 at 15:31, Rob Herring <robh@xxxxxxxxxx> wrote: > > On Mon, Dec 3, 2018 at 12:20 PM Simon Glass <sjg@xxxxxxxxxxxx> wrote: > > > > Hi David, > > > > On Sun, 2 Dec 2018 at 18:11, David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> wrote: > > > > > > On Wed, Nov 28, 2018 at 07:31:37PM -0700, Simon Glass wrote: > > > > Hi Rob, > > > > > > > > On Wed, 28 Nov 2018 at 14:51, Tom Rini <trini@xxxxxxxxxxxx> wrote: > > > > > > > > > > On Wed, Nov 28, 2018 at 03:47:22PM -0600, Rob Herring wrote: > > > > > > On Wed, Nov 28, 2018 at 3:31 PM Tom Rini <trini@xxxxxxxxxxxx> wrote: > > > > > > > > > > > > > > On Sat, Nov 24, 2018 at 08:42:19PM +1100, David Gibson wrote: > > > > > > > > On Wed, Nov 14, 2018 at 04:29:23PM -0800, Simon Glass wrote: > > > > > > > > > Hi David, > > > > > > > > > > > > > > > > > > We had a discussion today about a possible new v18 DT format[1] > > > > > > > > > > > > > > > > > > You have seen Frank Rowand's design from January[2]. Frank presented > > > > > > > > > material at the conference[3] and I wrote up something up too [4]. > > > > > > > > > > > > > > > > Yes, I didn't like the original proposal very much - overly > > > > > > > > complicated, but the revised one I suggested back looks reasonably > > > > > > > > do-able. > > > > > > > > > > > > > > > > Your proposal seems to have a rather different focus from Frank's - > > > > > > > > his is mostly about cleaner handling of overlays and similar > > > > > > > > extensions. Yours is mostly about size. > > > > > > > > > > > > > > > > Can I ask what's the concern here? I mean, first of all, I'm finding > > > > > > > > it a bit hard to believe that a few kiB of device tree really mean > > > > > > > > much in the context of a vaguely modern system. But more specifically > > > > > > > > is the concern in-memory size? Or size on persistent storage, disk or > > > > > > > > flash? Those two would be amenable to different approaches to > > > > > > > > mitigate. > > > > > > > > > > > > > > So, with respect to size, yes, for one example, modern 32bit Allwinner > > > > > > > SoCs are limited to either 32KiB or 24KiB and 64bit SoCs are limited to > > > > > > > 32KiB and that's our space for residing and executing from and holding > > > > > > > the device tree we're working from. > > > > > > > > > > > > You are referring to limits of what the bootROM can load for u-boot > > > > > > SPL cases, right? > > > > > > > > > > Yes. > > > > > > So, I gather this SPL is essentially a first-stage bootloader? I'm > > > > Yes. > > > > > wondering if fdt is actually the right tool for the job here. Could > > > you instead make just a hardcoded structure with the minimal known > > > values that the first stage loader needs to find the second stage, > > > which would include the full DT. I'm envisaging that you'd have some > > > tool for building that first-stage structure from the fdt, but that > > > would be done at build time, not runtime. > > > > This is the goal of the 'dtoc' tool in U-Boot. It creates header files > > and structs to hold data from the DT. Would you be open to upstreaming > > this? > > Are you aware Zephyr is doing something similar[1]? I'd think we'd > only want something in dtc if we can align with them. Even there's > different needs on the output, there's probably still some parts that > could be shared. I'm thinking things like address translation. I think I attended a talk on this at some point but I cannot remember any details. Something like [2]. I could perhaps get involved in that if there is any interest on the Zephyr side. The dtoc approach is to generate C structures rather than define CONFIG variables, thus allowing a bit more flexibility. Regards, Simon > Rob > > [1] https://docs.zephyrproject.org/latest/devices/dts/device_tree.html [2] http://events17.linuxfoundation.org/sites/events/files/slides/Zephyr%20Device%20Tree%20-%20ELC2017.pdf
