Messages in this thread | | | From | Rob Herring <> | Date | Mon, 16 Jun 2014 08:30:12 -0500 | Subject | Re: [PATCH] firmware: Add device tree binding for coreboot |
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On Fri, Jun 13, 2014 at 4:58 PM, Julius Werner <jwerner@chromium.org> wrote: >> This is just to export a fixed log to userspace (like a DMI table) or >> the kernel will actually use the data in some way? Based on the link, >> it looks like the former to me. > > I could imagine both. The link is an in-kernel driver that exposes a > log through a sysfs node (in a way that has already been established > on x86 systems, which find the location through EBDA or ACPI entries > instead). We are also using a user-space tool that reads the address > from /proc/device-tree and accesses it through /dev/mem. The areas can > contain many interesting entries (like the location of an early > framebuffer set up by the firmware), so I could also imagine use cases > where the kernel makes use of it directly.
I can be argued that the boot interface is DT and any configuration data should be put there in a common way. We don't really need yet another boot mechanism as we already have:
UEFI + FDT UEFI + ACPI "standard" bootloaders (e.g. u-boot, grub, barebox, etc.) + FDT
Allowing every bootloader to define its own boot interfaces would only result in a mess for both code and testing. I don't want to get into a debate about this now as it is not too relevant to this patch, but just want to highlight the resistance you will face going down this path.
>> Don't you need need to keep the kernel from allocating this memory by >> using one of the reserved memory mechanisms? The recently added one >> should be able to specific what the memory is reserved for IIRC. > > Our bootloader is carving the location out of the /memory node and > adding it to the device tree reserve map. As far as I know, that only > contains a list of raw start and size entries. At any rate, I think > it's useful (and in line with other bindings) to add a more explicit > node like this (if only to make it easier accessible through > /proc/device-tree).
Understand there are 3 different memory reservation bindings. The original "/memreserve/" method is indeed limited. What I think you should use is the binding documented in Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt. So you could do something like this:
reserved-memory { #address-cells = <1>; #size-cells = <1>; ranges;
/* global autoconfigured region for contiguous allocations */ linux,cma { compatible = "shared-dma-pool"; reusable; size = <0x4000000>; alignment = <0x2000>; linux,cma-default; };
coreboot_reserved: coreboot@fdfea000 { compatible = "coreboot"; reg = <0xfdfea000 0x264>, <0xfdfea000 0x16000>; };
>> /firmware is already used IIRC. What if you have other firmware such >> as Trustzone? > > I'm not quite sure how Trusted Foundations works and whether it would > even make sense to use it in parallel to coreboot, but it seems to be > using the /firmware/trusted-foundations subnode so that should be > fine. "firmware" seems to be used by other firmware implementations > (like "samsung,secure-firmware") which are similar in nature to and > mutually exclusive with coreboot, so I thought the node makes sense. > (The kernel should use the compatible string to find it anyway, so a > future name clash would not be world-ending.)
They are not mutually exclusive. What runs in secure world or not is entirely independent of non-secure boot. You may not care about it, but other platforms could.
Rob
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