On Mon, Mar 19, 2018 at 02:58:28PM +0100, Maxime Ripard wrote: > On Mon, Mar 19, 2018 at 11:20:19AM +0530, Srivatsa Vaddagiri wrote: > > * Maxime Ripard <maxime.ripard@xxxxxxxxxxx> [2018-03-18 19:09:16]: > > > > > > In addition to compiling DT code outside core kernel tree, we also want to merge > > > > the blobs back to respective blobs found in kernel build tree (soc.dtb or > > > > boardX.dtbo), as otherwise relying on bootloader to do all the overlay impacts > > > > boot-time. > > > > > > > > This brings up the need to merge two overlay blobs (fingerprint-overlay.dtbo + > > > > boardX.dtbo), which currently doesn't seem to be supported and which this patch > > > > series aims to support. > > > > > > If I understood you right, you want in your "feature" overlay to > > > depend on nodes that are only defined in your board overlay? > > > > Actually the feature overlay can depend on nodes that are both in soc dtb and > > board overlay. To explain this further, feature overlay can be split into two > > portions: > > > > feature-soc.dts -> this part represents feature DT code that is common across > > all board configuration using given SOC. This will attempt to changde nodes > > found only in soc.dts > > > > feature-boardX.dts -> this part represents feature DT code that is specific to a > > given board . It can attempt to change nodes in both boardX.dts as well as > > soc.dts > > > > We could compile both feature-soc.dts and feauture-boardX.dts as > > feature-soc.dtbo/feature-boardX.dtbo respectively and overlay them one after > > other at runtime (in bootloader), but that introduces impact to boot-time. This > > is the reason why we want to merge offline at compile time. > > > > feature-soc.dtbo needs to merge with soc.dtb (found in kernel obj tree) > > feature-boardX.dtbo needs to merge with boardX.dtbo (found in kernel obj tree) > > Right, but then, you just depend on something that is already depend > on something in the base tree (whether the base tree is just a single > tree or the aggregation of a base tree and previously applied > overlays). > > > > If so, why not simply merge the __symbols__ node when we apply an > > > overlay with the base tree, and just call fdt_apply_overlay as many > > > times as needed? > > > > Not sure if I follow you here. Please see my comment on not wanting > > to merge feature DTBOs at runtime in bootloader. > > fdtoverlay also allow you to build a single blob at build time. Um.. it does? AFAICT it's just a simple wrapper around the fdt_overlay_apply() function and won't merge overlays. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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