Re: [PATCH 2/2] mtd: rawnand: use unnamed union in struct nand_op_parser_pattern_elem

From: Masahiro Yamada <yamada.masahiro@socionext.com>
To: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Lucas Stach <dev@lynxeye.de>, Marek Vasut <marek.vasut@gmail.com>,
	Richard Weinberger <richard@nod.at>,
	Linus Walleij <linus.walleij@linaro.org>,
	Boris Brezillon <bbrezillon@kernel.org>,
	Janusz Krzysztofik <jmkrzyszt@gmail.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Stefan Agner <stefan@agner.ch>,
	Jonathan Hunter <jonathanh@nvidia.com>,
	Boris Brezillon <boris.brezillon@bootlin.com>,
	Thierry Reding <thierry.reding@gmail.com>,
	linux-mtd <linux-mtd@lists.infradead.org>,
	linux-tegra@vger.kernel.org,
	Brian Norris <computersforpeace@gmail.com>,
	David Woodhouse <dwmw2@infradead.org>
Subject: Re: [PATCH 2/2] mtd: rawnand: use unnamed union in struct nand_op_parser_pattern_elem
Date: Tue, 22 Jan 2019 17:00:54 +0900	[thread overview]
Message-ID: <CAK7LNAQvD03By1PQJ8KZG-UqX+NVQcL6JU-5a-2ZVVovdgBpEQ@mail.gmail.com> (raw)
In-Reply-To: <20190122084944.420fcd4a@xps13>

On Tue, Jan 22, 2019 at 4:50 PM Miquel Raynal <miquel.raynal@bootlin.com> wrote:
>
> Hi Masahiro,
>
> Masahiro Yamada <yamada.masahiro@socionext.com> wrote on Tue, 22 Jan
> 2019 16:42:55 +0900:
>
> > Although drivers do not directly get access to the private data of
> > instruction patterns, let's use unnamed union field to be consistent
> > with nand_op_instr.
> >
>
> Actually this is how we wrote it the first time. Then we got robots
> reporting that anonymous unions where not allowed with older (still
> supported) GCC versions and I had to do this:
>
>
> commit c1a72e2dbb4abb90bd408480d7c48ba40cb799ce
> Author: Miquel Raynal <miquel.raynal@free-electrons.com>
> Date:   Fri Jan 19 19:11:27 2018 +0100
>
>     mtd: nand: Fix build issues due to an anonymous union
>
>     GCC-4.4.4 raises errors when assigning a parameter in an anonymous
>     union, leading to this kind of failure:
>
>     drivers/mtd/nand/marvell_nand.c:1936:
>         warning: missing braces around initializer
>         warning: (near initialization for '(anonymous)[1].<anonymous>')
>         error: unknown field 'data' specified in initializer
>         error: unknown field 'addr' specified in initializer
>
>     Work around the situation by naming these unions.
>
>     Fixes: 8878b126df76 ("mtd: nand: add ->exec_op() implementation")
>     Reported-by: Andrew Morton <akpm@linux-foundation.org>
>     Signed-off-by: Miquel Raynal <miquel.raynal@free-electrons.com>
>     Tested-by: Andrew Morton <akpm@linux-foundation.org>
>     Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
>

Hmm, how come Andrew's compiler was fine with the following?

struct nand_flash_dev {
        char *name;
        union {
                struct {
                        uint8_t mfr_id;
                        uint8_t dev_id;
                };
                uint8_t id[NAND_MAX_ID_LEN];
        };
        unsigned int pagesize;
        ...
};

The current minimum version is GCC 4.6
(commit cafa0010cd51fb7)
but I am not sure if this restriction is remaining.

-- 
Best Regards
Masahiro Yamada