From: "Chan Kim" <ckim-mINagvnPBMnWF1p7bDn8Kw@public.gmane.org>
To: 'David Gibson' <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org>
Cc: devicetree-compiler-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: RE: A question about generated phandle during dtb=>dts conversion
Date: Wed, 3 Nov 2021 18:06:47 +0900 [thread overview]
Message-ID: <014201d7d092$21cb4050$6561c0f0$@etri.re.kr> (raw)
In-Reply-To: <YYH1H1bPHWS+NAte@yekko>
Hi, David Gibson,
Thank you for the answer. I can understand it now.
Best regards,
Chan Kim
> -----Original Message-----
> From: David Gibson <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org>
> Sent: Wednesday, November 3, 2021 11:34 AM
> To: Chan Kim <ckim-mINagvnPBMnWF1p7bDn8Kw@public.gmane.org>
> Cc: devicetree-compiler-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> Subject: Re: A question about generated phandle during dtb=>dts conversion
>
> On Tue, Nov 02, 2021 at 06:03:27PM +0900, Chan Kim wrote:
> > Hello, all
> > I extracted a dtb file from qemu execution (arm virt machine) and
> > converted the dtb file to dts file using dtc.
> > But for some node that is referenced by other nodes, the phandle is
> > generated like “phandle = <0x8000>” as shown below.
>
> Note that the value is generated by qemu and is in the dtb. It's not
> generated by dtc during decompilation.
>
> > apb-pclk {
> > phandle = <0x8000>;
> > clock-output-names = "clk24mhz";
> > clock-frequency = <0x16e3600>;
> > #clock-cells = <0x00>;
> > compatible = "fixed-clock";
> > };
> >
> > And another node is using this phandle like this. (the clocks is the
> > phandle for the apb-pclk above.)
> >
> > pl061@9030000 {
> > phandle = <0x8003>;
> > clock-names = "apb_pclk";
> > clocks = <0x8000>;
> > interrupts = <0x00 0x07 0x04>;
> > gpio-controller;
> > #gpio-cells = <0x02>;
> > compatible = "arm,pl061\0arm,primecell";
> > reg = <0x00 0x9030000 0x00 0x1000>;
> > };
> >
> > When I convert the dts back to the dtb, dtc doesn’t understand the
> > phandle and complains that it is not a phandle referenece.
> >
> > dts.dts:276.3-21: Warning (clocks_property): /pl061@9030000:clocks:
> > cell 0 is not a phandle reference
> >
> > I’ve checked event with this warning, the phandle reference is being
> > preserved through out the procedure.
> > So, if I want to extract a dtb and convert it to dts, edit some and
> > convert it back to dtb, how can I prevent this kind of phandle warning?
> > And why doesn't dtc add labels to the referenced nodes and let other
> > nodes use that label as phandle?
>
> The short answer is because dtc doesn't know it's a phandle. dtb is not a
> self-describing format - the properties are just bytestrings, and you need
> to know what you're expecting in there in order to decode them (that's
> what dt bindings give you).
>
> So the only way that dtc could know that those 4 bytes in the 'clocks'
> property are actually a phandle is by specifically knowing about the
> "clocks" property. dtc has *some* knowledge of specific properties in the
> checks, but it's far from complete (and complete knowledge of the bindings
> is pretty much out of scope for dtc).
>
> But.. for the normal case of writing a dts file directly, it's useful to
> get a warning if you don't use a reference somewhere you probably should
> (anywhere that's a phandle), so dtc does check that.
>
> So, I think basically in just the same way that you might expect generated
> or decompiled code to be rather messy and generate compiler warnings, so a
> decompiled dts might have messy things and generate warnings. You can
> switch off the warnings explicitly if you need (-Wno-clocks_property in
> this case).
>
> --
> David Gibson | I'll have my music baroque, and my code
> david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_
> _other_
> | _way_ _around_!
> http://www.ozlabs.org/~dgibson
next prev parent reply other threads:[~2021-11-03 9:06 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-02 9:03 A question about generated phandle during dtb=>dts conversion Chan Kim
2021-11-03 2:34 ` David Gibson
2021-11-03 9:06 ` Chan Kim [this message]
2021-11-05 3:57 ` 'David Gibson'
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