Hi,
<br />
<br />David, Grant thank you for providing the info.
<br />From your reply and the other sources what I gather is as below. Please confirm whether I am on the right track.
<br />
<br />1) Bootloader passing BDInfo:
<br />Here, I have to create a .dts file inside /arch/powerpc/boot/dts directory. dtc compiles the .dts file and creates a dtb. The kernel, dtb and boot-wrapper are then embedded in a cuImage.* file after make. We need to write the platform-specific fix-ups in the cuboot-*.c file. The bootloader will pass BDInfo struct to kernel. The kernel will also receive the dtb.
<br />The only kernel changes we need to do here are fixups in cuboot-*.c and creation of .dts file.
<br />
<br />2) Bootloader passing DT:
<br />Here, the booloader will directly pass the DT instead of BDInfo. The platform-specific code in simpleboot.c will get excuted. We don't have to do any fixups inside kernel here.
<br />I have queries with this approach -
<br />a) In this case, who creates DT? Do we need to use any tools to create a DT? or it can be created the same way by compiling the .dts file using dtc?
<br />b) From previous implementaions of other boards, I didn't see any platform specific fix-ups inside kernel being done? Why is so that in case of BDInfo we need fix-ups and here we don't?
<br />
<br />
<br />Please confirm my understanding of above to approaches. Also please suggest which way is better.
<br />
<br />Regards,
<br />Vinayak
<br />
<br />----------------------------------------------------------------------------------------------------
<br />From: David Gibson <david@gibson.dropbear.id.au>
<br />Date: Sun, Nov 22, 2009 at 2:50 AM
<br />Subject: Re: DTS for PowerPC 440 based board
<br />To: Vinayak Kale <vinayak.kale@gmail.com>
<br />Cc: linuxppc-dev@lists.ozlabs.org
<br />
<br />
<br />
<br />On Sun, Nov 22, 2009 at 12:16:59AM +0530, Vinayak Kale wrote:
<br />> Hi,
<br />> I am porting 2.6.31 for a PowerPC 440 core based board. I have couple of
<br />> queries. I would really appreciate if someone could answer since i couldn't
<br />> find info from other places.
<br />>
<br />> 1) Is it mandatory to create a DTS file?
<br />
<br />
<br />Roughly speaking, yes. You have to supply a device tree to the
<br />kernel somehow, so if the firmware doesn't supply one itself, you will
<br />need to create a DTS.
<br />
<br />
<br />> 2) If uboot passes BDInfo struct to kernel instead of DT blob, then in this
<br />> case does kernel creates FDT at run time?
<br />
<br />
<br />Not exactly. In this case the bootwrapper will be built with an FDT
<br />(compiled from a dts) built in. It will however tweak the FDT with
<br />information from the BDInfo before booting the kernel proper.
<br />
<br />
<br />> 3) I believe in case of DTS, the kernel picks up the h/w info from DTS blob
<br />> so we need not hardcode any register addresses etc inside kernel other than
<br />> in dts file. What happens in case of uboot passing just BDInfo struct. How
<br />> do we specify the register addresses etc?
<br />
<br />
<br />There's always a device tree which specifies register addresses. If
<br />the firmware only supplies a BDInfo, then the kernel wrapper must have
<br />a device tree built in. In practice that will always be built from a
<br />dts, though it doesn't have to be in theory.
<br />
<br />--
<br />David Gibson | I'll have my music baroque, and my code
<br />david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
<br /> | _way_ _around_!
<br />http://www.ozlabs.org/~dgibson