Re: [boot-wrapper PATCH v3] Makefile: avoid dtc warnings on re-compiling DTB

From: Vladimir Murzin <vladimir.murzin@arm.com>
To: Andre Przywara <andre.przywara@arm.com>,
	Mark Rutland <mark.rutland@arm.com>
Cc: Jaxson Han <jaxson.han@arm.com>, linux-arm-kernel@lists.infradead.org
Subject: Re: [boot-wrapper PATCH v3] Makefile: avoid dtc warnings on re-compiling DTB
Date: Mon, 31 Jan 2022 17:33:29 +0000	[thread overview]
Message-ID: <9226f733-bf45-fdc2-90db-c401e7cd7cd6@arm.com> (raw)
In-Reply-To: <20220131163122.2188634-1-andre.przywara@arm.com>

On 1/31/22 4:31 PM, Andre Przywara wrote:
> When we add the PSCI nodes to the provided DTB, we use dtc to de-compile
> the blob first, then re-compile it with our nodes and properties added.
> 
> In our input DTB the proper phandle references have already been lost,
> all we see in the DTB is phandle properties in the target node, and some
> numbers in the clocks and gpios properties:
> ===========
> 	clk24mhz {
> 		compatible = "fixed-clock";
> 		#clock-cells = <0x00>;
> 		clock-frequency = <0x16e3600>;
> 		clock-output-names = "v2m:clk24mhz";
> ->		phandle = <0x05>;
> 	};
> 	...
> 	serial@90000 {
> 		compatible = "arm,pl011", "arm,primecell";
> 		reg = <0x90000 0x1000>;
> 		interrupts = <0x05>;
> ->		clocks = <0x05 0x05>;
> 		clock-names = "uartclk", "apb_pclk";
> 	};
> ===========
> dtc warns that those numbers might be wrong:
> =========
> <stdin>:177.6-27: Warning (clocks_property):
>  /bus@8000000/motherboard-bus@8000000/iofpga-bus@300000000/serial@90000:
>    clocks: cell 0 is not a phandle reference
> ....
> =========
> The proper solution would be to use references (&v2m_clk24mhz) instead,
> as there are in the source .dts file, but we don't have that information
> anymore, and cannot easily recover it.
> 
> To avoid the lengthy list of warnings, just drop those checks from the
> dtc compilation run. This disables more checks than we want or need, but
> we somewhat trust in the original DTB to be sane, so that should be
> fine.
> Since those warning options are not supported by older dtc versions,
> introduce a compatiblity check before using them.
> 
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> ---
> Hi,
> 
> this replaces the reverted version of the patch, adding runtime detection
> of dtc's compatibility.
> Works fine with a clueless dtc 1.4.1.
> 
> Cheers,
> Andre
> 
>  Makefile.am | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/Makefile.am b/Makefile.am
> index 40bc5d6..08e304a 100644
> --- a/Makefile.am
> +++ b/Makefile.am
> @@ -162,8 +162,16 @@ $(COMMON_SRC):
>  model.lds: $(LD_SCRIPT) Makefile
>  	$(CPP) $(CPPFLAGS) -ansi -DPHYS_OFFSET=$(PHYS_OFFSET) -DMBOX_OFFSET=$(MBOX_OFFSET) -DKERNEL_OFFSET=$(KERNEL_OFFSET) -DFDT_OFFSET=$(FDT_OFFSET) -DFS_OFFSET=$(FS_OFFSET) $(XEN) -DXEN_OFFSET=$(XEN_OFFSET) -DKERNEL=$(KERNEL_IMAGE) -DFILESYSTEM=$(FILESYSTEM) -DTEXT_LIMIT=$(TEXT_LIMIT) -P -C -o $@ $<
>  
> +# Run dtc with an given command line option to check support for it.
> +define test-dtc-option
> +$(if $(shell echo "/dts-v1/;/{};" | $(DTC) $(1) -o /dev/null 2>&1),,$(1))
> +endef
> +
> +DTC_NOWARN  = $(call test-dtc-option,-Wno-clocks_property)
> +DTC_NOWARN += $(call test-dtc-option,-Wno-gpios_property)
> +
>  fdt.dtb: $(KERNEL_DTB) Makefile
> -	( $(DTC) -O dts -I dtb $(KERNEL_DTB) ; echo "/ { $(CHOSEN_NODE) $(PSCI_NODE) }; $(CPU_NODES)" ) | $(DTC) -O dtb -o $@ -
> +	( $(DTC) -O dts -I dtb $(KERNEL_DTB) ; echo "/ { $(CHOSEN_NODE) $(PSCI_NODE) }; $(CPU_NODES)" ) | $(DTC) -O dtb -o $@ $(DTC_NOWARN) -
>  
>  # The filesystem archive might not exist if INITRD is not being used
>  .PHONY: all clean $(FILESYSTEM)
> 

FWIW, 

Tested-by: Vladimir Murzin <vladimir.murzin@arm.com>

Thanks
Vladimir

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