[RFC] FDT fix for 64 bit platforms
jchandra at freebsd.org
Sat Oct 15 16:33:06 UTC 2011
On Sat, Oct 15, 2011 at 8:43 PM, Nathan Whitehorn
<nwhitehorn at freebsd.org> wrote:
> On 10/15/11 01:12, Jayachandran C. wrote:
>> On Sat, Oct 15, 2011 at 2:01 AM, Nathan Whitehorn
>> <nwhitehorn at freebsd.org> wrote:
>>> On 10/14/11 14:10, Jayachandran C. wrote:
>>>> I'm planning commit this -CURRENT if there an no objections.
>>>> 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
>>>> Review or testing from device tree users will be welcome.
>>> Why not use offsets into the FDT rather than full pointers? I believe
>>> phandles greater than 32 bits violates the FDT spec, and declaring that
>>> FDT can't itself be larger than 4 GB seems reasonable.
>> 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.
> 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.
Well, the existing FDT code returns 0 as the invalid handle and I do
not want to change that in this commit.
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
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