linux-kernel - Re: [PATCH 2/2] mtd: rawnand: use unnamed union in struct nand_op_parser_pattern

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Message-ID: <20190122090830.118eb6be@xps13>
Date:   Tue, 22 Jan 2019 09:08:30 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Lucas Stach <dev@...xeye.de>, Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        Linus Walleij <linus.walleij@...aro.org>,
        Boris Brezillon <bbrezillon@...nel.org>,
        Janusz Krzysztofik <jmkrzyszt@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Stefan Agner <stefan@...er.ch>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-mtd <linux-mtd@...ts.infradead.org>,
        linux-tegra@...r.kernel.org,
        Brian Norris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH 2/2] mtd: rawnand: use unnamed union in struct
 nand_op_parser_pattern_elem

Hi Masahiro,

Masahiro Yamada <yamada.masahiro@...ionext.com> wrote on Tue, 22 Jan
2019 17:00:54 +0900:

> On Tue, Jan 22, 2019 at 4:50 PM Miquel Raynal <miquel.raynal@...tlin.com> wrote:
> >
> > Hi Masahiro,
> >
> > Masahiro Yamada <yamada.masahiro@...ionext.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@...e-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@...ux-foundation.org>
> >     Signed-off-by: Miquel Raynal <miquel.raynal@...e-electrons.com>
> >     Tested-by: Andrew Morton <akpm@...ux-foundation.org>
> >     Signed-off-by: Boris Brezillon <boris.brezillon@...e-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;
>         ...
> };
> 

It is probably not :)

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

That's right, can you please test if this limitation is still
ongoing wit GCC 4.6?


Thanks,
Miquèl