Re: [Minios-devel] [UNIKRAFT PATCHv4 4/9] plat/common: Introduce fdt_{address, size}_cells_or_parent helpers

[Sharan Santhanam <sharan.santhanam@xxxxxxxxx>]

Hello Julien,


On 4/10/19 10:52 AM, Julien Grall wrote:
> On 10/04/2019 09:43, Sharan Santhanam wrote:
> > Hello Jia He,
> >
> > On 4/10/19 7:43 AM, Jia He wrote:
> > > Hi Sharan
> > >
> > > After I dig more on it, I would like to rework this patch 4/9.
> > >
> > > Please see the comments from libfdt author [1]
> > >
> > > "
> > >
> > >    * #address-cells and #size-cells describe the format of addresses
> > >      for children of this node, not this node itself.  So if you're
> > >      looking to parse 'reg' for this node, you *always* need to look at
> > >      the parent, not just as a fallback.
> > >
> > >    * #address-cells and #size-cells are *not* inherited.  If they're
> > >      missing in a node, then the format for its children's addresses is
> > >      2 cell addresses and 2 cell sizes, it is *not* correct to look at
> > >      the next parent up for these properties.
> > > "
> > >
> > > So, seems I should
> > >
> > > parent = fdt_parent_offset(fdt, nodeoffset);
> > > naddr = fdt_address_cells(parent, nodeoffset);
> > > nsize = fdt_size_cells(parent, nodeoffset);
> > I agree, we could do this way as well.
> >
> > My suggestion was based on the previous patch where we implement 
> > interrupt-cells. For interpreting the interrupt property, we read 
> > interrupt-cell of the parent within the function fdt_interrupt_cells. 
> > In this function we pass the node offset of the child. We could try 
> > and keep the APIs consistent for similar type of functions.
> Parsing #address-cells and #size-cells is different from parsing 
> #interrupt-cells. The first two are found in the parent node, while the 
> latter is found in the interrupt controller node (looked up via 
> interrupt-parent).
Sorry, I did not mean it that way.

In the function fdt_interrupt_cells we expect the "offset" argument to 
be the node containing the interrupt property identify the 
interrupt-controller using the interrupt-parent whereas in the functions 
fdt_address_cells_or_parent we expect the "offset" argument to be the 
offset of the parent as we read the address-cell property within it.
My suggestion was to keep the offset argument represent the node 
containing the interrupt and reg property respectively.

> Cheers,
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