Hi Manivannan, Sorry for the delay. I'll try to get to this today or tommorrow. -Frank On 04/25/18 00:34, Manivannan Sadhasivam wrote: > Hi Frank, > > Did you had time to look into this? Especially I'd like to hear your > opinion on the first pain point I have mentioned. I can understand > that the whole point on introducing the of_overlay_fdt_apply() API > is to remove the duplication of overlay FDT unflattening, but do you have > any idea of how we can make this API work with overlay nodes appended > to the base DTB? > > Thanks, > Mani > > On Thu, Apr 19, 2018 at 08:08:04PM +0530, Manivannan Sadhasivam wrote: >> Hello Everyone, >> >> I have just started working on the Devicetree Overlay Manager support in >> kernel. The idea is to merge overlays at boot time specified via some >> interface like kernel command line. The motivation for this work comes from >> Overlay Manager [1] submitted by John last year. The mechanism which I have >> been working on is an extension to John's work. It focusses on addressing >> Rob's comments on the Overlay Manager which involves having multiple ways >> to load overlays. >> >> Proposal: >> ========= >> >> 1. Pass all devicetree overlays via following methods: >> - Overlays appended to base DTB >> - Individual overlays built into kernel as firmware blobs >> - Any other ways? >> >> 2. Specify overlays to load via kernel command line as below: >> - overlay_mgr.overlays=<overlay1,overlay2,...> >> >> 3. Merge only the specified overlays during boot time. First look for the >> overlay in the base DTB. If it is found, just apply it, else defer to firmware >> load approach. >> >> The Overlay Manager code is expected to be very simple and will just do the >> above mentioned work. Later on, it will be extended to support dynamic >> modification of overlays from userspace with some additional security >> features like having a property listed in the base devicetree for only >> allowing changes to the current node and its child nodes, etc... >> >> Pain Points: >> ============ >> >> 1. Starting from 4.17 we don't have any API exposed from DT core to merge >> individual devicetree nodes. We only have of_overlay_fdt_apply() function >> which takes the whole FDT. This will work very well for the firmware approach >> since we will pass the overlays blobs but not for overlays appended to base DTB, >> where we will pass individual overlay nodes. >> >> 2. Using firmware load method will force us to have this Overlay Manager code >> at late_initcall level since firmware class exists only in fs_inticall level, >> which might be too late for some devices. >> >> 3. This whole approach is not expected to work very well (still not yet tested) >> on DSI based devices since it needs to be present at very early during boot >> process. >> >> The Overlay Manager propsed here will be board agnostic and it should work on >> all platforms supporting DT. This will be a _very_ useful feature for the >> development boards such as 96Boards, Raspberry Pi, BBB etc... and also for >> production ready devices. >> >> So, I'd like to hear suggestions/feedbacks for the above mentioned proposal & >> pain points and hope to land the most awaited feature in kernel. >> >> Regards, >> Mani >> >> [1] https://lkml.org/lkml/2017/10/10/20 > -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
