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





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

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