Date: Sat, 15 Oct 2011 18:55:24 +0200 From: Rafal Jaworowski <raj@semihalf.com> To: Marcel Moolenaar <marcel@xcllnt.net> Cc: "Jayachandran C." <jchandra@freebsd.org>, FreeBSD Current <freebsd-current@freebsd.org>, Nathan Whitehorn <nwhitehorn@freebsd.org>, Andrew Duane <aduane@juniper.net> Subject: Re: [RFC] FDT fix for 64 bit platforms Message-ID: <B149C582-DA23-4D19-879F-1A5D6D4861C7@semihalf.com> In-Reply-To: <82FC5404-7B93-426B-9303-14BD8BC37542@xcllnt.net> References: <CA%2B7sy7AhU7WLuabx6HCtUgvEtUHWBmGe-eP=N8L9VknM65r-mg@mail.gmail.com> <4E989C28.3030606@freebsd.org> <CA%2B7sy7Ba6zrRGQuon%2B7FPk8EhgnpYLWTGv0EAPy0pdRXJfc3ZQ@mail.gmail.com> <4E99A319.20801@freebsd.org> <CA%2B7sy7DRTM%2Bmgxx4ogEwttLtsaVyWA5XQ4bnfJ54rQLmHZ34Pw@mail.gmail.com> <82FC5404-7B93-426B-9303-14BD8BC37542@xcllnt.net>
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On 2011-10-15, at 18:48, Marcel Moolenaar wrote: >=20 > On Oct 15, 2011, at 9:33 AM, Jayachandran C. wrote: >=20 >> On Sat, Oct 15, 2011 at 8:43 PM, Nathan Whitehorn >> <nwhitehorn@freebsd.org> wrote: >>> On 10/15/11 01:12, Jayachandran C. wrote: >>>>=20 >>>> On Sat, Oct 15, 2011 at 2:01 AM, Nathan Whitehorn >>>> <nwhitehorn@freebsd.org> wrote: >>>>>=20 >>>>> On 10/14/11 14:10, Jayachandran C. wrote: >>>>>>=20 >>>>>> I'm planning commit this -CURRENT if there an no objections. >>>>>>=20 >>>>>> In the current implementation, phandle is used to store a pointer = to >>>>>> the location inside the device tree. Since phandle_t is u32, = this >>>>>> will not work on 64 bit platforms. With this fix, the phandle is = the >>>>>> offset from the start of device tree pointer 'fdtp', which will = be 32 >>>>>> bit. >>>>>>=20 >>>>>> Review or testing from device tree users will be welcome. >>>>>>=20 >>>>>> JC. >>>>>=20 >>>>> Why not use offsets into the FDT rather than full pointers? I = believe >>>>> having >>>>> phandles greater than 32 bits violates the FDT spec, and declaring = that >>>>> the >>>>> FDT can't itself be larger than 4 GB seems reasonable. >>>>=20 >>>> I am actually using the offset from the beginning of FDT (fdtp) as >>>> phandle. I cannot use the usual fdt offset (after off_dt_struct) = as >>>> phandle, because in that case offset of 0 is valid, but phandle 0 >>>> should not be valid. >>>=20 >>> Why shouldn't phandle 0 be valid? The invalid phandle is -1. This is = one of >>> the problems with our existing FDT code -- it makes all kinds of = wrong >>> assumptions like this about IEEE 1275. >>=20 >> Well, the existing FDT code returns 0 as the invalid handle and I do >> not want to change that in this commit. >>=20 >> If the return value is really wrong, we will need a bigger exercise = to >> change the return value and fix any callers which are affected by = that >> change. >=20 > It should be fairly easy to change the base from fdtp to the "usual" > fdt offset, so let me propose the following: >=20 > 1. JC commits what he has and based on the current code. > 2. We get all the facts on the table. I say this because I > read different and contradictory things (0 being an > invalid phandle in OF, negative phandles exist, etc). > 3. We change the implementation, if such is warranted, in > a separate effort. >=20 > The point really is that 0 is an invalid phandle right now, > right or wrong, and JCs changes are based on that. I see no > problem proceeding on the path we're on, while we discuss > what's the correct implementation and whether or not we > should have a course change... >=20 > Thoughts? The patch looks fine to me, but we didn't have a chance yet to test it = on any PPC/ARM system, have you, Marcel? Regarding the phandle validity = I need to recall the context as this was a while back and I don't quite = remember all constraints and motivations. Rafal
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