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From: Peter Maydell <peter.maydell@linaro.org>
To: Palmer Dabbelt <palmer@dabbelt.com>
Cc: "open list:RISC-V" <qemu-riscv@nongnu.org>,
	Alistair Francis <Alistair.Francis@wdc.com>,
	QEMU Developers <qemu-devel@nongnu.org>,
	David Gibson <david@gibson.dropbear.id.au>
Subject: Re: [PATCH v2 1/3] device_tree: Add a helper function for string arrays
Date: Sat, 9 Nov 2019 15:59:24 +0000
Message-ID: <CAFEAcA_3jgn1WrX2wpBd+sCYe=nNaqA2POvaZkj-NsSyT2N9bQ@mail.gmail.com> (raw)
In-Reply-To: <20191108194758.17813-2-palmer@dabbelt.com>

On Fri, 8 Nov 2019 at 19:48, Palmer Dabbelt <palmer@dabbelt.com> wrote:
>
> The device tree format allows for arrays of strings, which are encoded
> with '\0's inside regular strings.  These are ugly to represent in C, so
> the helper function represents them as strings with internal '\0's that
> are terminated with a double '\0'.  In other words, the array
> ["string1", "string2"] is represeted as "string1\0string2\0".
>
> The DTB generated by this function is accepted by DTC and produces an
> array of strings, but I can't find any explicit line in the DT
> specification that defines how these are encoded.

> +/*
> + * This uses a particularly odd encoding: "strings" is a list of strings that
> + * must be terminated by two back-to-back '\0' characters.
> + */
> +int qemu_fdt_setprop_strings(void *fdt, const char *node_path,
> +                             const char *property, const char *strings);

The clean API for this would be to use varargs so you could write

qemu_fdt_setprop_stringlist(fdt, node, prop, "arm,armv8-timer",
                            "arm,armv7-timer");

and have it do the assembly into the encoding that fdt expects.
That would require us to do a bit of allocation-and-freeing
to assemble the string, of course, but then we only do fdt
creation at startup.

NB: I think that this is a good idea but not-for-4.2 material,
so if you wanted your sifive board change to go into 4.2 you
should probably start with the simple approach and leave the
refactoring for the next release cycle.

thanks
-- PMM


  reply index

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-08 19:47 [PATCH v2 0/3] device_tree: Allow for and use string arrays [Was: RISC-V: virt: This is a "sifive, test1" test finisher] Palmer Dabbelt
2019-11-08 19:47 ` [PATCH v2 1/3] device_tree: Add a helper function for string arrays Palmer Dabbelt
2019-11-09 15:59   ` Peter Maydell [this message]
2019-11-10 19:44     ` David Gibson
2019-11-08 19:47 ` [PATCH v2 2/3] ARM/virt: Use fdt_setprop_strings() Palmer Dabbelt
2019-11-09 15:56   ` Peter Maydell
2019-11-10 19:47     ` David Gibson
2019-11-08 19:47 ` [PATCH v2 3/3] RISC-V: virt: This is a "sifive,test1" test finisher Palmer Dabbelt

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