Re: [PATCH 1/4] of: Add of_parse_phandle_with_opt_args() helper function

From: Robin Murphy
Date: Wed Sep 30 2015 - 11:39:43 EST

Hi Marc,

On 22/09/15 18:52, Marc Zyngier wrote:
of_parse_phandle_with_args() is slightly inflexible as it doesn't
allow the (unusual) case where the #*-cells property is not defined.
In order to support this, introduce of_parse_phandle_with_opt_args()
which assumes that #*-cells is zero when it is not defined,
as required by the msi-parent binding

This is done by turning __of_parse_phandle_with_args into an even
bigger monster, which is a bit frightening.

A monster indeed; I can't quite figure out the exact effect this change has on of_count_phandle_with_args(), but I have a lingering doubt it may be something undesirable, since AFAICS that's now going to proceed from where it would have errored out before, with a count of -2.

I think it might be nicer to implement this by passing an extra "assume zero if #cells not found" boolean to __of_parse_phandle_with_args().

Alternatively, what's the actual likelihood of legacy bindings being mixed in with new ones? Could we not simply mandate that anyone adding an MSI controller with #msi-cells to a DT must ensure any existing nodes are also updated with #msi-cells = 0, and keep the legacy workaround self-contained in the MSI layer? e.g. paraphrasing from patch 2/2:

msi_np = of_parse_phandle(np, "msi-parent", 0);
if (!of_property_read_bool(msi_np, "#msi-cells"))
return parse_this_thing(...);
while (!of_parse_phandle_with_opt_args(np, "msi-parent"...
if (parse_this_thing(...))


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