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

[Julien Grall <julien.grall@xxxxxxx>]

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).
Cheers,

--
Julien Grall

_______________________________________________
Minios-devel mailing list
Minios-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/minios-devel